| wok |
Is any one using the long-throw 135mm lense from diyprojectorcompany (alan). I ordered the kit with the lense and fresnals to match - the NZ exchange rate is a killer - doubled the price.
Anyway - is anyone using this lense and what are your results?
I have a 15" cmv1515 lcd and a 400w metal halide. I figured with the bigger lense and lcd i would need the biggest light i could find.
The lense is marketed so you can set the projector much further back from the screen and still get a managable size image - it sounded good to me - if anyone has an opinion or results from using this kit can you let me know.
When the lense kit shows up i will put the bad-boy together and post some results.
Also what is your opinion on reflectors behind the light - growers use gloss white painted surfaces on their reflectors - would this be better than a mirror finish on a metal reflector?
Im going to use an aluminum reflector and polish it till it glows - give me your opinion on this.
Cheers everyone - these forums have made my desicisions much easier for parts selection!!!
keep up the good work! |
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| ancorp |
| I got an identical-looking lens with the same specs, seems like an excellent lens, worked well for my 17" flat crt to project it onto a 60 in screen. |
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| slizm |
| ancorp dp you have any pics of your results and your pj? Is your lens capable of doing 90-100 inches? |
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| ancorp |
hmm, i dont have an LCD projector.
I just tested it with a CRT. Im going to build a Projector out of a 13 or 14" NON-flat tv, and a 175mm diameter triplet that I got a good deal on. |
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| slizm |
| do you know what model opaque your lens came out of? |
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| ancorp |
heres the auction Ive won on ebay
Right Here
Its a Bell & Howell The Spotlight, my guess the original ts-1
Ive seen many ts-5's on ebay for under 100$ that seem to have about the same lens specs, just looks abit different, it had writing on the ts-5 lens. |
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| slizm |
| I have a couple of the VU Lyte III Opaques but I can't seem to find the specs on lenses. |
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| ancorp |
well you can find out most by yourself with just a ruler, and a good eye!
Diameter, Focal lenght, overall lenght, and even type (doublet, triplet, achromatic doublet, etc) can be found easily. |
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| wok |
| is anyone actually going to post a reply about my first question? |
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| Rox |
| quote: | Originally posted by ancorp
I got an identical-looking lens with the same specs, seems like an excellent lens, worked well for my 17" flat crt to project it onto a 60 in screen. |
were the corners 100% focused? anyway your throw on this test was quite short (2meters?) that means the lens_back--tv distance was long (51cm?) so it is not the way most of us will use it. Iīm triyng to determine the FOV of 135mm lens but i canīt believe manufacturers donīt know it. |
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| jcbklyny |
| You can get 100% focus corner to corner with the 135mm lens but you need one of the lumenlab 650mm fresnels. LL's wrong 790's work 100% corner to corner... but only up to 8 or so feet from the screen. When you move it back 10-15 feet you need the 650's. |
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| Rox |
i think this thifference on the throw can be fixed placing the lamp closer to the rear fresnell.
You mean 17" works right with 135 triplet? do you know the FOV JCB? your store has a pdf wit specs but i canīt download them. |
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| jcbklyny |
| I emailed the company and am still waiting on a reply. The ones I have are the same as DIYlabs (diyprojectorcompany). I'm out right now so if your interested place your order with Alan. |
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| Rox |
| i would order if i knew the FOV and it suits me. |
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| Rox |
JCB wrote: I emailed the company and am still waiting on a reply
no news? Why does nobody know the FOV of this lens? I think it is not interesting for you to make it known. All the tryes makin 17" with 135 triplet that i see are black cornered. I think that the FOV is just too thin for this kind of TFT.
Would like to hear coments about it. |
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| ancorp |
| quote: | Originally posted by Rox
were the corners 100% focused? anyway your throw on this test was quite short (2meters?) that means the lens_back--tv distance was long (51cm?) so it is not the way most of us will use it. Iīm triyng to determine the FOV of 135mm lens but i canīt believe manufacturers donīt know it. |
Hi Rox,
Sorry for the really delayed reply (missed your post). Yes, the corners seemed 100% focused (I can actually do a re-test if it really matters) Remeber its a 17"CRT, thats like a 16" LCD. I also Tested the lens with a 20" TV, and it seemed to be right on the limits (got the corners, but the lens had to be almost dead center, no lens shifting). Yes, the throw was about 2 meters, same with the TV, abit more, with an image of about like 70-100 inches. With a proper enclosure and screen, a 20" tv with this lens will give a nice 60-100 inch picture (abit on the dark side, but with proper service mode adjustments, shouldnt be a problem)
Hope this helps,
Cheers,
Alex |
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| Rox |
thanks for your information but it is not very usefull my friend.
the throws you are using are too short. Thats why you need to place the lens so far from the image source (so 17" 16"real image enters the triplet even thought its small FOV.
The isues come when you use 17" tft real (17") and the trhow is 3m lets say. then the triplet is so close that the tft is outside of its FOV. So it does not work at the corners.
But the only thing i would like to know is the FOV value of this lens. Its getting hard to find it!!!!!! sellers seem not to share it with us, i wonder why :D |
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| ancorp |
| Hey, Id like to help you, and test it at like 120", but the monitor simply doesnt have enough brightness...:( |
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| Squalish |
Rox, I direct you to this thread:
http://www.lumenlab.com/forums/index.php?showtopic=5230
His site has more info.
Basically, he got it to work by using the lamp at 220mm instead of the 330mm focal length. This made the effective focal length I think ~450mm, and combined with taking apart the triplet, got him reasonably sharp (I didn't see close enough for screendoor, but individual pixellation is visible) images.
I'm thinking that that's how I'm going to do it. |
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| Guy Grotke |
I think we don't see FOV specs for most lenses because it depends on the throw distance. But we could see a maximum field angle spec. Then you could calculate the maximum field of view at a certain LCD-to-lens distance.
But this assumes that a lens cuts off all the light beyond a particular angle. That is not true. Both duplets and triplets usually have an internal stop aperature to make the image illumination even from all angles specified in the performance requirements. (In most triplets, it is the smaller diameter negative lens in the middle.) Without the stop, the central part of the image would get more light than the edges, so it would be brighter.
The maximum field angle is the circle where the combination of the outer lens diameters, the mounting tube, and the internal stop begin to block some light. But light from beyond that circle will still make it through the lens. As you get farther from the circle, less light will get through so the image of those points will get dimmer. You won't even see the difference in brightness if only 10% of the light is blocked. So then were exactly is the boundary of the useful FOV?
Another useful question to think about: Are 17" LCD corners dim because they are beyond the useful FOV of the projection lens, or is the problem really with uneven illumination by the fresnels? If we assume a throw distance of 122 inches with a 450 mm fl lens, then the LCD-to-lens distance will be 526 mm. (This should give a 100" image.) The LCD half diagonal distance is 215.9 mm. By Pythagorean Theorum, the distance from the lens to the corner of the LCD is 569 mm. If we take the inverse sin of (215.9 / 569) we get 22.3 degrees. That is the half angle, so the full field angle is 44.6 degrees. Triplets generally work perfectly out to a 45 degree field angle. (By the most conservative definition of maximum field angle.) So it looks like all of the 17" LCD would be within the lens's FOV.
You can use the same method to calculate the required field angle for a 220 mm fl condensor fresnel. 215.9 mm half width with a 220 mm lamp-to-fresnel distance gives you a full field angle of 88.9 degrees! So maybe somebody with dim corners on their 17" LCD should try using a longer focal length condensor fresnel! |
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| Rox |
jeje, yes, i know him, is a very good friend of mine :D, what he did is get the lens elements closer so the focal lengh increased and this way he could proyect from his 17" lcd. We believe the FOV value of the lens increased as well. His 135triplet "native" results are not very good. But is the few ones that have posted results. I believe the native FOV is not compatible AT A RASONABLE THROW.
Hi guy grothke, long time didnīt post to you :D.
one of the repplys to one of the two 135 triplet sellers everibody knows when i asked about the FOV value was that the manufacturer told him it depens on the aplication. Actually i am not sure but i think it is not true. I think that the lens has a FOV value defined by construction just like the focal lengh (it is defined by construction and is independent to the aplication).
now, it is true that in some aplications (short throw cases) the needed fov could be smaller than the max fov of the lens. But i would say that the native fov from the 135 is poor for 17".
the fov of a common triplet you say it is 45 degrees, well, if i take my laser and bend it to the 80 triplet, the angle is much more than 45 degrees(i can reach 60degrees before the laser turns off). Iīwill do some test on it but have no 135 triplet.
lets see your math;
your 100" screen is 2meters wide moreless. I donīt know if it is a standar image but my friend diyeitor (first 17" diymaker from spain) has 2,5 m wide imagesize. he has a litle bit more throw than your example (so triplet is something closer to the tft). The fact is that his corners are black. He has moved the bulb front/back to see if it was the light the problem (it could be that the light cones were outside of the triplet but it was not the case, you know some OHP have a wheel to move the lamp position so ligh cones can be adjusted for each trhow?) so the conclusion was that with such a screen size the FOV was not sufficent.
I would like to see some results of your example (100") at 3M throw distance, and full screen 17" image source. Do you know where can i find some?
do you think manufacturers donīt know the FOV of their lens?
thanks for your atention, i use to have a very good time with you :D |
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| Guy Grotke |
I agree with the manufacturer: I am sure all lens manufacturers know the maximum useful field angle of their lenses, but the FOV of a triplet depends on what you are doing with it because FOV is the diameter of the circle on the object plane. With different throw distances, the object plane (the LCD) will be different distances from the lens. But what does remain constant is the field angle.
You saw that some part of your 80 mm diameter triplet would pass a laser beam at a 30 degree angle from the central axis. But I think that only a small portion of the lens would do that. Within the useful field, the same area of the lens (ie. square mm)will pass rays to the other side. As the source of those rays is moved around, different parts of the lenses may be used, but the total area remains the same. The maximum useful field angle is where a smaller area of the lens will pass rays. That will make the image progressivly dimmer past that angle.
Sorry, I can't run this test for you: I don't have a triplet. I have some DIY duplets with lower field angles and a Rodenstock tessar that has a larger field angle.
I think your friend with the 17" projector should take the projection lens out and put his eye (covered with very dark glasses or welding goggles) right where the lens goes. Then he should look at the corners of the LCD. I bet they are much dimmer than the center. That would prove the problem is with the condensor system instead of the projection lens. If that is the problem, then one solution is to change to a longer focal length condensor fresnel with matching spacing between the lamp and the condensor fresnel. |
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| Rox |
So i confussed the fov value with the field angle. I thought they where the same thing.
now my rearch will be to determine the field angle :D.
when my friend had the triplet natively, he proyected from his 17"lcd as well. He did some test; with the backlight of the lcd, he just placed the triplet at the same position that would be for 2,5M wide image and 3,5M throw. (there was a dimm image but the corners where black as well)
when you use such image source, without field fresnell, like crt projectors people do, the light is not very effective since it it homnidirectional, but this test shows it is not the front fresnell focal lenght problem. He did what you are saying as well (looking trhow the triplet very close to look if he could see the corners of the lcd, and he told me that he couldnīt see them).
just let me check this, the max fov value for our aplication should be equal to the field angle?
I just havent seen results for 17" and donīt know why, i know lot of people started doing one. And the two only results i have seen where blackcornered.
thanks for you replys. |
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| Guy Grotke |
Field Of View is the diameter of the circle in which a lens delivers 100% of the light. When you take a photograph with a large format lens (just like a projection lens but the light is going the other direction) the image will be focussed at one focal plane, some distance from the lens. If the object being photographed is at a far distance (like a landscape), then the focal plane will be the lens's focal length from the lens. Then the FOV will be the product of the maximum field angle and the focal length.
If the object being photographed is much closer (like a group protrait), then the focal plane will be farther away from the lens. The maximum field angle will stay the same, but the FOV will be larger since the cone of light spreads out over a greater distance. This is like an LCD projector: The FOV is larger because the LCD to lens distance is longer than the lens's focal length. |
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| Guy Grotke |
There are several things that can cause dim corners in the screen image. Each one can be determined by careful troubleshooting, and then improved.
1) A precondensor lens may not be throwing awide enough cone of light to your condensor fresnel. Test: With everything else removed from the projector but the light engine and precondensor lens, put a white piece of paper exactly where the condensor fresnel goes. See if it all gets lit. Fix: Adjust precondensor lens position or use a longer focal length precondensor lens.
2) The distance from the lamp arc to the edges of the condensor fresnel is farther than the distance to the center. This makes the edge light a bit dimmer than the center light (inverse square law). Test: Same as #1. Look at the relative brightness on the paper. Fix: Use a longer focal length condensor fresnel and increase the lamp to fresnel distance. This will make the center to edge closer to the same, but both will be dimmer.
3) Lamp to condesnor fresnel distance may be off. Test: Add the condensor fresnel and move the piece of paper to 10 cm after the fresnel. The condensor should throw an even rectangle of light on the paper in the same size as the fresnel. Fix: Adjust the lamp to fresnel distance until it does. If you can't get a nice even rectangle of light, try another fresnel.
4) With an non-split design, the extreme angles at the corners may exceed the viewing angle of the LCD. Test: Install fresnels & LCD, then look at the lit LCD screen from the projector lens position. (NOT through the projector lens.) You will need really dark glasses or welder's goggles for this. Drive the LCD with a uniform white image. Are the corners lit? Fix: Change to a split design so the light goes through the LCD at 0 degrees, or change to a better LCD.
5) The LCD may be too wide for the projection lens. Test: If test 4 passes but you still get very dark corners on the screen, then this is probably the cause. Fix: Get a projection lens with a wider maximum field angle, or try moving the projector closer to the screen. That increases the LCD to lens distance so you might see more of the LCD on the screen. |
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| Rox |
thanks, now i see FOV has nothing to do with what i am asking.
So the max field angle is defined by construction then isnīt it?
I told my friend to test his lens with a laser like i did with my 80T.
the results are this; max half angle with T80 = 45 degrees.
max half angle with T135= 20 degrees.
about the dim corners posible causes; he has both fresenlls behind the lcd, and the lamp position is the best he could find. I worked out the critical angle at the very corner and found it was 18,7degrees. So i donīt think it is to much angle for the lcd.
but i think the best test is the one he did with the lcd unstriped. with its native light. So the light is uniform on all the screen, he placed the triplet where it should be, but the results were blackornered as well.
could you help me about the field angle spec on this lens? nobody answers me. Thanks |
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| Guy Grotke |
| Maybe that triplet does not have a wide enough field angle for a 17" LCD. I have DIY duplets I made for $20 US, that have wider field angle than that. |
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| Rox |
yes thats what i am triyng to work out befory buying one but its getting hard.
i asked it to JCB 6 times right now.
I think manufacturers have the specs off the lens, is a s easy as asking them. |
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| Rox |
| quote: | Originally posted by jcbklyny
. LL's wrong 790's work 100% corner to corner... but only up to 8 or so feet from the screen. When you move it back 10-15 feet you need the 650's. |
there are no wrong lens, just wrong setups.
if we start talking about wrong lens, i would start with 135 triplet field angle. |
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| jcbklyny |
| quote: | | there are no wrong lens, just wrong setups. |
Trust me, there IS such a thing as having 'the wrong lenses' for certain setups and no matter how much you move and adjust it will never work the way it SHOULD!
and Rox, enough with the 135... really. You talk more about that lens then any 15 people on any one of the DIY projector boards and you dont even have one! BUY ONE... and then talk. Or dont and drop it.
-JCB
www.diybuildergroup.com |
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| Rox |
its glad to me to tell you that i received information from awi.
They arenīt good news for you. But i am still working on it. You will have news soon. |
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| Rox |
Ok here it is;
THE MAX FIELD ANGLE THIS LENS WAS DESIGNED FOR IS: 24 DEGREES
What does it mean? it was designed for 24 degrees, and you can use a larger field angle but the lens was not designed for more than 24.
So 45 degrees need for 17" are very far and the 41 degrees for 15" are closer but something far as well.
Now this valious information has been reveled. Each one can do what hell the wants.
Good luck. |
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| Guy Grotke |
I wonder if that was the half angle they quoted you? (The maximum field angle from the central axis.) I calculated a full field angle of around 49 degrees for this lens, (using limited size data), which is very close to twice the 24 degrees you claim. This is also a much more typical full field angle for a triplet design.
If they wanted a projection lens with a full field angle of just 24 degrees, then they could have done it much cheaper. |
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| Hezz |
ROX,
The FOV angle is usually quoted for the angle which is the angle between the axial center of the lens and the angle for which there has been correction made. This is because most lens systems are symetrical. Therefore the usable total angle is 48 degrees. Now the longer the FL is the farther the lens is away from the image source so the bigger image it can focus.
If you take a 48 degree angle and move it out from a flat surface about 15 to 19 inches and lengthen the angle lines out until they intersect the image plane. That is about the image size that the lens can focus.
If you don't have CAD software you can easily do this with a large piece of cardboard or paper, a protractor and a straight edge.
I will sketch a CAD drawing for you so you will know the total theoretical size that the lens can image. Be back in a few minutes.
Hezz |
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| Hezz |
ROX,
If you can interpret this sketch one thing should become obvious.
This lens should in theory work with up to a 21 inch LCD. But you would probably need to project at least a 200 - 250 inch screen to get it to work. This is just estimate.
This is going to give some guys with a 600 watt metal halide bulb some
dangerous ideas. If your room was big enough and you made a monster projector you could use a 21 inch LCD and have a really large image.
Hezz |
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| Rox |
well, i didnīt know that the field angle was the half angle so twice would be the correct one we can use to our setups.
iīll check it with the manufacturer.
24 degrees (12+12?)
OR
48 degrees (24+24?)
sorry about confusing you. |
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| Rox |
| quote: | Originally posted by Guy Grotke
I calculated a full field angle of around 49 degrees for this lens, (using limited size data), |
Please could you tell us how?
Those are first hand specs;
450mm EFL ,
F=3,6
Clear aperture= 125mm
barrel lenght=150mm
midle element F stop aperture=109mm |
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| Guy Grotke |
The clear aperature and the middle element aperature would be important if we were using this triplet for photography. But we are not!
The fresnels are used to create a cone of light that could be focussed at the same plane as the optical center of the lens. The edges of that cone form a virtual aperature, since there is no light outside the cone. Assuming you use a 24 mm arc, 220 and 550 mm fl fresnels, and the LCD to lens distance is 528 mm, then the focussed arc image would be 60 mm long.
Draw a full-scale picture of the LCD and lens cross-section with the LCD on the left side. Draw the 60 mm arc image as a vertical line through the center of the triplet. Then draw a line from the upper edge of the arc image to the upper edge of the lens barrel. Measure the angle of that line from the central axis. That is the half angle. You can also extend the line to the left until it crosses the plane of the LCD. If it passes above the vertical line that represents the LCD, then all of the light passing through corner pixels can get to the arc image in the lens, and thus out the other side to the screen.
Of course, this is just a simple estimate. It assumes that the optical center of the lens is at the physical center, which may not be true. It also assumes the triplet is symmetrical, so light that gets in along the arc image path will also clear the opposite barrel. But it should be pretty accurate, since the lens could focus a clear image of a pixel even if some of the light from that pixel was blocked. |
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| Rox |
i would say that if we consider the refraction by the first and third lens the angle would be even smaller. forget by now the arc lengh and try to imagine a ligh ray from first lens upside passing throw midle lens elemnt and get outs from botton third elemnt. I think this is the critical ligh stop last ray. then if you consider the refranction by those two lenses (midle lens is not working) you would see the angle of the ray coming from lcd is smaller than the angle inside the triplet. Also we can say that the light would be dimer because of the arc lengh, but i donīt want to complicate more.
here is what i mean; |
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| Guy Grotke |
Since we don't know the focal lengths of the individual lenses that are in the 450 mm fl triplet, we can't really say what happens to the light inside it. If the lenses were +450 mm fl, -450 mm fl, +450 mm fl, then I think the first lens would refract rays at the edge by about 8 degrees. But then the middle lens would refract them back by some amount.
Instead of guessing about what happens inside the triplet, my estimate is based on the size and directions of the light paths coming from opposite corner LCD pixels for this particular application. In the drawing below, the blue lines represent the path of all of the light going through an LCD corner pixel. (I know that this is the path, because if I remove the triplet and put a piece of white paper where the center lens would go, I can see the focussed 60 mm long arc image.) The width of each light path will actually be a little bit smaller than 60 mm inside the middle lens, because of refraction by the first lens.
The green lines represent the path of all of the light going through the opposite corner pixel of the LCD. If we send light along these paths, at least we know it will get into the lens and most of the light from each path will get converged to a single spot on the screen 10 feet away. If we want to know exactly what happens inside the triplet, then we need to know the lens materials, the 6 surface curves, and the spacing. Then we can put all of that in a ray tracing program to make some better predictions.
But maybe all of this is not necessary: If anybody reading this has one of these triplets, they could use a laser pointer to find the maximum field angle through the lens in just a minute or two, and then post the result here! |
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| ancorp |
| quote: | Originally posted by Guy Grotke
But maybe all of this is not necessary: If anybody reading this has one of these triplets, they could use a laser pointer to find the maximum field angle through the lens in just a minute or two, and then post the result here! |
I have a laser pointer, and an identical looking lens... how can I measure the fov with a laser pointer? |
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| Hezz |
ROX,
You are thinking but you are in error. The refraction caused by the lenses system is taken into account as is part of the chromatic correction and these issures are taken into account when the FOV is stated.
All light is refracted by all of the lenses in differing amounts. The light being refracted does not lessen the stated FOV because the designed FOV assumes that such things are occuring and the lens correction is what takes this into account. The FOV of a lens system is not based on simple geometry but we have used simple geometry to show how the light cone of the fresnel will fit in the aperature of the lens. As long as the field fresnel light cone is within the FOV of the lens there will be little wasted light output. But this is a seperate issue from the objective lens system's FOV.
The FOV of the objective lens system is not based on such simple geometry. It is determined by the corrected refracted indexes and dispersion of the combined lens system. Each lens element is a different glass type and shape and spacing from the others lenses. This is what is used to correct for the different amounts of refraction at different light frequencies.
Repeat, the stated FOV is an engineered level of performance and assumes that there is refraction therefore the stated FOV is what it is unless the company was lying to you. But what they have stated is inline with what Guy has measured and what common lens design sense and experience indicate it shold be.
Hezz |
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| Inkog |
UPS should be delivering this lens to me tomorrow! (It only took 45 days or so for DIYPC to ship it to me :smash: )
I have been following this discussion for quite some time and will be happy to do some experimentation in attempts to help resolve these issues once and for all.
I have a laser pointer around somewhere also... |
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| Guy Grotke |
You just lay the lens on its side on a table with the screen 10 feet away, then point a narrow laser beam through it. You should see a laser spot on the screen. (Use some masking tape or a couple of small paperback books to hold the lens in place.)
Create a line on the table (on paper maybe?) that is perpendicular to the lens central axis, and 530 mm back from the center of the lens tube. Then you can move the laser pointer (with its tip on that line) as you keep it pointing at the center of the lens. (Not the center of the first lens surface, but the center of the entire lens tube.)
When the screen spot dissappears, you may have gone past the maximum field angle. You can try and move the laser direction a bit on the first lens surface to see if you can get the screen spot to reappear. If not, then you have gone past the maximum angle. Move the laser pointer back along the line until the spot just reappears on the screen. Measure the angle of the laser beam relative to the central axis. If you don't have a protractor, you can just measure the distance of the laser pointer tip from the central axis along the 530 mm perpendicular line. If that is more than 8.5 inches, this triplet will work fine for a 17" LCD.
Tip: Make sure the laser pointer is at the same height above the table as the middle of the triplet, (ie. 67.5 mm?) |
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| Rox |
Hezz said; "The FOV of the objective lens system is not based on such simple geometry. It is determined by the corrected refracted indexes and dispersion of the combined lens system. Each lens element is a different glass type and shape and spacing from the others lenses. This is what is used to correct for the different amounts of refraction at different light frequencies"
I agree with you Hezz, SO the test Guy Grotke described (my friend did it also with his 135 tirplet and my laser) i would say it is not the Field angle, this test would show the max critical light angle, mean the last light angle (light stop angle), but i believe the fov is smaller because it is not geometrical defined but the aperture where the focus, light intensity, aberrations... are the minimal expected by design as hezz said.
I still have not received the reply from manufacturer about the field angle 24 (12+12) or 48 (24+24) but i think the spec they will give will be more acurate than any test we could do. |
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| Hezz |
Rox,
I think that they may not respond to you because it is common knowledge that the stated FOV is measured from the lens axis to the furthest corrected light angle. So if they told you that it is 24 degrees then the total usable imaging angle is twice that number.
I thinks Guys test was still reasonably accurate in describing the approximate FOV. It would'nt make much sense from a design point of view to make a lens system this large have only a 24 inch total usable imaging angle because it would have little utility except in the case where a huge amount of light ( several kilowatts) had to be put through the lens at a narrow angle.
Hezz |
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| Rox |
well, if they have told me that the angle is X, then they have not problem telling me where is the angle defined :D.
I still have no reply, but will tell you soon. Just wonder, have you ever seen corner to corner focused image with 15"?
this is focused ok at center but i would not say it is "corner to corner focus" check it.
http://img.photobucket.com/albums/v...7/DSC01328b.jpg |
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| Guy Grotke |
The laser beam used in the test I described will be a very narrow beam, so it will let you determine the maximum angle at which 100% of the light in a particular ray will get through the lens. Once you know that angle, then you can use it to see how wider beams (ie. all the light from a corner LCD pixel) will pass through the lens.
You can refer to the last drawing I included in a post. The laser will show you if the upper edge of the corner-pixel beam can get through the lens. Then you can rotate the laser slightly to see if the lower edge of that beam will also get through the lens. If both edges of the beam get through the lens, then it will work fine for a 17" LCD projector.
Also, I think that most lens designs are made so the edges and the center have "good enough" performance. Some distance part way between the edges and the center, the performance will be the best. But that particular distance does not define the FOV. The full field of view uses much more of the lens. |
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| Guy Grotke |
Isn't that image from your friend's projector that uses a 330 mm fl field fresnel? That probably has more to do with the poor corner appearance than the use of the 450 mm fl triplet.
gg |
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| Rox |
yes, it is my friends 135 native results with 330.
but could you show me better images of 15" with 135? people say they have " corner to corner" but never seen it.
I would like someone to prove it. JCB,could be one that could demostrate it. I would like to see close photos like this one i posted.
I really would like to check it is posible, nothing else.
about the laser test, it is the max angle the triplet can work on ok, but how can we know the field angle from there? i measured the 80 triplet with my laser and found it is 120 degrees, (60+60)
but it is known that the lens does not work very well with 17" so the field angle is much smaller than the max laser angle.
So what can we learn with 135 triplet laser angle? |
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| Rox |
Ok the 24 degrees are full angle, 12+12 so it is not 48 (24+24) as most of us would like to be.
it is 24 the specs of field angle this lens was designed for, it has been confirmed by manufacturer just now.
If large panels are going to be used with this lens, there needs to be some sacrifice with the focus on the corners.
Good luck with it. |
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| ace3000_1 |
| quote: | | Isn't that image from your friend's projector that uses a 330 mm fl field fresnel? That probably has more to do with the poor corner appearance than the use of the 450 mm fl triplet. |
I agree on that and the majority of the time people have trouble with dim corners because their frensels are not flat or not matched to the projection lens. Or, their condenser is not right or the distance to the rear frensel from the source light is not correct to the rear frensels focal ect.
Heaps of things cause hot spots and dark corners, the projection lens is realy the last thing you take a look at.
As a rule of thumb in what ive found, the longer the projection lens barrel on a given set diameter, the shorter the field of veiw.
Trev:) |
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| Rox |
| quote: | Originally posted by ace3000_1
I agree on that and the majority of the time people have trouble with dim corners because their frensels are not flat or not matched to the projection lens. Or, their condenser is not right or the distance to the rear frensel from the source light is not correct to the rear frensels focal ect.
Heaps of things cause hot spots and dark corners, the projection lens is realy the last thing you take a look at.
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I think you are wrong there. The first thing to check should be the field angle from the triplet, if it is too small (24 degrees are very poor) do not try to have corner to corner focus there).
Mean the manufacturer does not recoment to work where the field angle is larger than 24 because it was not designed for this. Is that easy. Anyway i agree that the propper field fresnell would do better work.
Data: my friend after modifiyng the triplet, has much better focuse images but still is ussing 330 field fresnlell even with a larger focal triplet, how would you xplain it? |
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| ace3000_1 |
| quote: | | Data: my friend after modifiyng the triplet, has much better focuse images but still is ussing 330 field fresnlell even with a larger focal triplet, how would you xplain it? |
I think thats obvious.......
| quote: | | I think you are wrong there. The first thing to check should be the field angle from the triplet, if it is too small (24 degrees are very poor) do not try to have corner to corner focus there). |
No im not wrong, why would someone go out and buy a triplet for a large panel that has a 24deg FOV in the first place? Thats what would be wrong ;).
I know what your trying to get at Rox and your talking from a different level of mind. Why would anyone go out and buy the wrong parts and try to make them work? thats kinda pointless in my eyes and why its important to do a full scale drawing in the first place to see what optical characteristics you need. Doing it the otherway is like a dog chassing its tale, you will be there forever trying to get things right.
If you want my honest opinion, the way we do things isnt the right way to go about it. Running a projector in full paralelle is the best way to have a perfectly focused image with even brightness, but unfortunatley doing that on our sized pannels would be pointless, costly and heavy. A 7inch lcd is still too big in my eyes, both for efficency and for image quality. A 1-2inch is ideal.
Trev:) |
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| Rox |
| then what do you think about the compatibility of 135 triplet and 15" lcd? (not to mention 135 triplet and 17") |
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| ace3000_1 |
I wouldnt buy it, if you only have 12deg per side thats kinda too small. I did rough rough scetch and i mean rough with 2 rulers measured 15 inches apart (i know thats not the width of the lcd but lets work on diagonal here) at one end, and measured up 450mm to a point. Then i got out a protractor and measured the deg per side, it requires about 20deg per side so you would need a triplet atleast with a 40deg FOV.
That triplet has a nice arperature, but the FOV sux. The OHP triplets he sells would give a better image i would suspect as their FOV is around 65mm (32.5mm per side) but the arperature is kinda small which in turn gives us limited focusing ability, and therfore you could get dark corners again on the OHP lens. If you use a frensel that has aspherically contorured groves the image may sufice but still wouldnt be perfect. The Vari triplet from Brainchild may work better though im not sure of its FOV. If it has a FOV larger then 50mm (combined) and an arperature of 100mm, then youve got it made (providing your using the right frensels).
Trev:) |
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| ace3000_1 |
Realy on a lens that has a FOV of 12deg per side its only good for a projector run in a paralelle fashion, that would yeild great results.
Trev:) |
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| Rox |
i agree.
But brainchild has deleted this item thought. (there is not at store since couple of weeks)
I believe this 135 triplet needs to be done some sacrifice with the focus on corners when we have 15" even. |
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| ace3000_1 |
| quote: | | I believe this 135 triplet needs to be done some sacrifice with the focus on corners when we have 15" even. |
Ya i agree, its probally relying on its large arperature to focus the sides not the FOV in which would make the corners smudged.
I was reading what you had to say in the other thread about having to see a 15inch lcd perfectly focused on the corners with this lens, i do agree with you, its kind of impossible. Some think that if its looks focussed it is focused, but get up close to the pixels and you will soon see that its not, well, its focused but smudged lol. Thats fairly normal in most of our setups, people dont like to admit this but its a fact of reality from using the optics we use currently available to us from diy online stores. Its also cos we arent running things in a paralle manner, the way we run our projectors isnt the best way in the imaging world.
Trev:) |
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| Dazzzla |
Trev ya back, u been on a holiday :D
DJ |
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| ace3000_1 |
I wish mate, been busy doing other things lol, im going on a holiday soon though :). My projector will be finnished this year aswell :eek:, all on paper just a matter to find the time to build it now.
Trev:) |
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| Rox |
well, i have received more information about the lens but it is confusing me. Now they say that the 24 degrees field angle is at the side of the wall. And at LCD side it is 38.7 degrees field angle.
Well, can somebody tell me how is it posible? i guess the light could go in both directions so the more restrictive angle is the closer to the reality (i would say 24 degrees). Or we can do a midle angle with both and say it is overal that field angle;
(38,7+24)/2=31.3 degree field of view.
I just donīt understand it. I think the manufacturers donīt know exactly what am i asking for.
Thats what they told me;
if there are 24 degrees in any side, then this would be the most restrictive. Any suggestions? (I am yet in contact with them to clarify this) |
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| ace3000_1 |
Rox, who drew the pic? you or them?
If its 24deg per side it should JUST work on a 15inch panel, i wouldnt expect mirricles though on the edges. I do realise this isnt the case though.
Trev:) |
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| Inkog |
That would explain the term "long throw" right? The angle of light leaving the triplet would be smaller than the angle entering the lens.
It sounds like that if you have the correct field fresnel, corner to corner focus and light distrobution should be possible. |
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| Rox |
I drow it with the information they gave me.
The angels are full angle, do not think they are half. The only confusion is that at LCD side (left) they said it is 38,7 full angle (19,3 + 19,3 half angles) but they say as well that on wall side (Right) it is 24 degrees angle (12+12) then if you do some math, you can see that there is image being projected on 38,7 angle so I wonder what does this 24 degrees on triple wall side field angle mean.
If the performances of the lens are only aceptable inside this 24 degrees, then the 38,7 degrees of LCD side has no sense. Please does anybody know what the hell is happening? |
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| Rox |
inkog then if the image enters from 38,7 degrees and outs from 24 degrees, what focal lenght have you got?
it is not compatible with only one focal and one magnification and one throw, you you understand it? |
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| ace3000_1 |
| quote: | | The angle of light leaving the triplet would be smaller than the angle entering the lens. |
Should be the same both sides bud, aleast of what ive seen in my lenses, vari triplets have a slight diff. That angle will only change if you move the lens closer or further from the lcd to focus, and it will still be the same on both sides at those magnifacations.
Trev:) |
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| ace3000_1 |
| quote: | | inkog then if the image enters from 38,7 degrees and outs from 24 degrees, what focal lenght have you got? |
That would have a negative focal if it was doing that, or the front ellement is less powerful then the back which imo is pointless for projecting an image unless you want a throw of 10m+ lol.
Trev :) |
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| Rox |
the focal of the lens would be positive always, but this long throw concept inkog has think about is not correct (there would be 2 focal lengh or two throws or two whatever, i mean that this system is not compatible (has no solution).
I also would say that the field of view angle needs to be simetrical to both sides. But i think that it could be that this angle they told me could be the angles where the aberrations have been minimized at this angle. (just a thought) I just want to know the field angle!!!!!! :( :( :(
what do you think about the midle point 31 degrees? can we accept this as field angle? anyway it is not 42 degrees (needed for 15" and 100" image)
I thought i had arrived to the field angle but now i think i have to start again :( Could you help me on it as well? maybe more people asking for it would do a faster correct reply (and your english would be much better than mine as well :D)
Rox, still on it. |
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| ace3000_1 |
| quote: | | the focal of the lens would be positive always, but this long throw concept inkog has think about is not correct (there would be 2 focal lengh or two throws or two whatever, i mean that this system is not compatible (has no solution). |
I think it has a solution, your right about having the lens being always with a possitive focal too, i meant a difference in between the front a back lenses. I think its either that or the lens inbetween the front and back lens has been alterd to give the difference in angles, though for that realy to work well, it takes a lens with a whole lot more then just 3 lenses (typically 7-9).
Trev:) |
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| Rox |
yes, i believe the lenses are different (is for this rason that the optical center is not at fisical center but at 1,5cm closer to the rear lens.
but if we have a lcd filling the 38 degrees back field angle and we have a proyected image filling a 24 degrees front field angle, this wonīt give you 450mm focal triplet. Have a try, you would see there is not solution. (i think that 450mm focal is not questionable right now :D)
this dual field angle is very confussing. I donīt think it is that way. |
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| ace3000_1 |
The center lens in a triplet is normally a DCV with a FOV the same on both sides of the overal projection lens, if you have the side facing the rear lens more concave then the front, the light diverges into a narrower beam for the front lens. That would change your FOV.
Its also an idea of mine to run a projector in paralelle from what we run now lol. Shhhhhhhhh
Its very possible to have a focal of 450mm, its just the focal of all of the lenses combined together, but its got me wondering if the focal is the same on both sides.
Your friend with his lens, did he turn it around and see any difference?
Trev:) |
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| Inkog |
DIYPC lists the focals like this on their website:
Rear Focal Length (actual): 380mm
Overall Focal Length (effective): 450mm
Please note I do not even pretend to know much about optics, but humor me...
Would those specs not explain the narrower angle leaving the lens?
Anyone actually configured their setup using the lens at the actual focal length of 380mm?
I'm at work now, but when I get home I'll draw out a raytrace of the lens and these new angles and see if I can make a correlation to the differences in the Rear FL and Overall FL.
Someone more knowledgeable then me, try plugging in these different focals on the respective sides of the Throw Distance calculator and see what you come up with. I'll do the same.
I now have this triplet and 2x 330mm freesnels and will do some experimenting tonight regarding this. I just finished my light engine and this is my next step anyway. |
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| ace3000_1 |
I just did a test on the diylabs ohp triplet, the rear FOV is about 80deg and the front 40, that would explain why the lens worked better one way then the other :clown:
Trev:) |
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| Rox |
well, 450 is the conbined focal of the three lenses, thats true. But this equivalent lens is what we refer to the optical center. Is like if there it was a 450 mm focal thin singlet rigth there.
If we take the triplet outside and place under the sun, then we can focus the light into a point. Well, this point will be 38cm from the rear lens and 450mm from the optical center of the triplet. Thats what back focal means. If we turn around the lens, then the focal point will still be at 450mm from the optical center, but now it will be 35cm from the "rear" lens. (rear because it is the front lens but turned around). The focal of the triplet will always be 450, back focal lengh is only a trick, considering the focal point like if the optical center was at rear lens, thats only for design consideration, never think you have 380mm focal triplet. |
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| Rox |
| quote: | Originally posted by ace3000_1
I just did a test on the diylabs ohp triplet, the rear FOV is about 80deg and the front 40, that would explain why the lens worked better one way then the other :clown:
Trev:) |
how did you measured it? |
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| ace3000_1 |
Laser. There are a couple of ways to do it but its hard to explain the otherway, basically you can do it just by looking at the lens on the right angle and measuring the FOV that way with a protractor. I did this lens both ways and it worked out the same. Imo laser is abit more acurate though and easier.
Draw a center line, place the lens on the line being in the center and project a laser through it. Mark off how far you can go to both sides of each lens with the laser before the image distorts and then measure. Do it on both sides of the projection lens and one side on the ohp diylabs lens is diff to the other. The top lens is also a diff shape the the bottom as the internal lens is also. The lens with the less FOV is flatter and is a DCV. The one with the wider FOV is PCX or similar and all lenses are the same diameter.
The internal lens is more concave on the 80deg side and flatter on the 40 so i was right :) .
Trev:) |
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| Inkog |
Ace,
So are you telling us that the information from the manufacturer is more than likely correct?
Rox,
That kind of make sense.. I think. :D Guess I was way off :cannotbe: |
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| Rox |
| quote: | Originally posted by ace3000_1
how far you can go with the laser before the image distorts and then measure |
mmm, i thought you did this way. let me tell you i did this test as well. Iīll tell you my results but first lets coment something;
"before the image distors" thats so relative..... i donīt think we can conclude a field angle. In fact i donīt know the criteria the manufacturers measure the field angle.
In my test i did not measure till it get distorted, i measured till it stoped (mean nome degrees more ligth was stoped, no light passing throw the lens). My measurement was 120 full angle (60 + 60 half angles) the same 32cm focal triplet as you. Well, can we conclude anyting? i would say no.
I mean, i belive there is a critical angle where the performences are lets say 50% of the central axis performances, then we can define a field angle this way for instance.
Example; A light bulb with included reflector, has a angle of aperture spec. This angle is very easy to determine it is the angle where the light intensity is half the intensity measured on the central axis. Thats how they determined it. But how the hell is matematicaly determined the field angle of a lens? I donīt know so i canīt determine one. |
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| ace3000_1 |
| quote: | | In my test i did not measure till it get distorted, i measured till it stoped (mean nome degrees more ligth was stoped, no light passing throw the lens). My measurement was 120 full angle (60 + 60 half angles) the same 32cm focal triplet as you. Well, can we conclude anyting? i would say no. |
LOL, i think mines fairly right, from memory the specs on the diylabs triplet has somthing like a 70 or 80deg FOV so i must be close. I dont do it till it like starts to distort or where the light cuts out, you see a sweet spot that all of a sudden drops away very rapidly and thats where i took my measurment, they wer combined angles aswell not per side.
Its a shame your not in madrid as i could show you what i mean and how i do it. Ive got some big condensers here that you can clearly see the FOV with your eyes, that same FOV i see with my eyes i soon see on the screen :), and see what the lens has as in limits in the real world environment. Prety much the shorter the focal and the larger the lens is the wider the FOV (not counting projection lenses with varible FOV's :D ). One thing i think you may be mixed up on is the clear arperature and the FOV in your measuring, to this day i havnt found a lens with a full side to side FOV and you wont either, its typical of them having a ratio of 3 arperature and 2 FOV so 2/3 of the lens is FOV. Though not aways somtimes its higher other times its less, it just depends on the design and type of the lens.
In the manufactures test labs im sure alot of them use lasers for the fov (did read that somwhere though ages ago), they use paralelle light for the focal finding. There is a formula for the FOV on a single lens, stuffed if i know what it is on a multi ellement lens, kinda gets complicated then.
Trev:) |
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| Guy Grotke |
Rox,
You DID determine the maximum field angle of the lens with your laser test. You know that light can get through the lens at a certain angle. It just may not give you very good performance at that angle. But "good performance" is a relative term.
LCD projection lens don't have to be all that good! The maximum spot sizes used for triplet design are good enough for photography. Film grain sizes are very small compared to the size of an LCD pixel. If a projection lens can get most of a pixel's light within the 2 mm pixel space on the screen, then it is good enough.
If you can get all the light through a corner pixel into the lens, so the most extreme ray is less than the maximum field angle, then all of that light will get through the lens. Here is a drawing of the first lens surface of the triplet. The red oval is the light that comes through one corner pixel. (It has the oval shape because it comes from all the areas of the lamp arc.) Since the part of the oval closest to the edge of the lens has a lower angle from the central axis than the maximum angle, all of this light will get through the lens. |
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| Rox |
ace my good friend, :D if it was 70 degrees field angle, we could use 19" lcd with 32cm triplet :D and you know that 15" is the largest we can use with it.
where did you see it is somewhere 70 degrees the field angle for this 80 triplet? i would say it is far from reality. (i stimate 50 degrees in the best case for this lens)
Why donīt we trust on manufacturers specs? mean who thought it is not 450 mm the focal of the 135 triplet? why shouldent the filed of view be 24? |
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| Guy Grotke |
Here is what happens if the fresnels are not working right. The blue oval is all of the light going through a corner pixel. Half of it is falling outside the triplet, so it will not get to the screen.
There are other factors that all contribute to making the corners dim:
1) The condensor fresnel geometry: A 220 mm fl fresnel for a 15" LCD makes the corners 1.8 times dimmer than the center, just by the inverse square law of light intensity.
2) In a non-split design, the LCD may not pass as much light at the corners because the viewing angle is higher.
Many people have built great projectors using the 450 mm triplet and 15" LCDs, so I think your 24 degree FOV figure is too low. |
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| Rox |
well, i am all the time using the same example;
My good friend diyeitor, the famous 135 triplet srtipper, has better image with the same 330 field fresnell when he modified the triplet. We donīt know the actual focal lengh, in fact it is very easy to measure the projection size and the trhow and we can determine the focal, but the only important thing is that the larger focal triplet (lets say 50cm focal) works very well with 330 field fresnell, you only need to check his last results.
then, please start thinking about the field of view angle istead of the field mismaching fresnell.
You know what?, i think the 450mm focal is not true. i think the manufacturers lie on this as well (ironic). |
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| ace3000_1 |
| quote: | | ace my good friend, if it was 70 degrees field angle, we could use 19" lcd with 32cm triplet and you know that 15" is the largest we can use with it. |
The highest lcd size on the triplet i have and tested works on a 17inch lcd. If you wer to get a longer focal one which are readily avail you can run a 19inch through em no probs. The ohp lenses are designed to have a wide feild of veiw, they are made that way for the stage they have to illuminate, also they would make the FOV wider on a ohp lens to elliminate distortions on the edges for when projecting text.
With my findings of the rear lens being about 80deg FOV and the top being about 40deg FOV, that doesnt neserserally mean that the overal FOV of the lens is 80deg, maybe they combine it ?
You got any answers guy?
The stated FOV for a typical ohp projection lens like mine is about 65-75deg. Ill try to find you a page that states this.
Imo its interesting now that we may have found a differing FOV triplet lens, now we can go and make stuff :).
Trev:) |
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| Inkog |
| quote: | | Imo its interesting now that we may have found a differing FOV triplet lens, now we can go and make stuff . |
:devilr: What kind of stuff?!? :devilr: |
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| Guy Grotke |
>You got any answers guy?
Nope, sorry! If I had one of those 450 mm fl 135 mm diameter triplets then I would try some FOV tests with a thin laser beam and some projection tests with diffuse backlighting on a 17" transparency.
But I don't have one of them. :clown:
I guess the folks that have them will just have to experiment a bit to see what they can actually do with different size LCDs and fresnel systems. (I know that most of the people happy with them are using a lumenlab long fl field fresnel.)
I do have a 600 mm fl Rodenstock process lens that has a terrific maximum field angle. I had to block bits of light leaking around the frame holding my 15" LCD, because this lens projected them on the wall (off the normal screen). My frame is about 1 3/4" wider than the LCD, so I think this lens would work for a 19" LCD. |
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| ace3000_1 |
| quote: | Originally posted by Inkog
:devilr: What kind of stuff?!? :devilr: |
LOL, ive got a few tricks up my sleeve, including a new light engine that recycles lost light, ill try that in a few days :).
I basically made that comment as the more we know or discover things, it opens up our horizons in constructing our own custimizable lens system with available on the shelf parts. Making a projection lens isnt that hard, and the more we learn about them, the closer we come to customising/building our own.
Trev:) |
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| Rox |
| quote: | Originally posted by ace3000_1
The stated FOV for a typical ohp projection lens like mine is about 65-75deg. Ill try to find you a page that states this.
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Yes please.
And to you that would like to meassure the field angle, if we donīt know the criteria, how could we measure the angle?
I mean I could say; This is the point where I CONSIDER THE MAXIMAL ABERRATIONS FOR MY SETUP, SO HERE IS MY MAXIMAL FIELD ANGLE. But this is not the criteria manufacturers use.
For instance, Ace says that 32focal tirplet does good work with 17" (we should know the throw he uses, since is very important as well) then others say that it is 16" the maximun LCD we can use with it. The only value i would agree with is the one stated by the manufacturer specs, this is the functionality of the specs, so enginers do know if it will work or not before they try it.
If someone finds the exact criteria to determine the Field angle, then ok, you can meassure it using the same criteria as manufacturers but until then i will not trust on any subjetive meassurement of field angle. |
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| Me2! |
| quote: | | LOL, ive got a few tricks up my sleeve, including a new light engine that recycles lost light, ill try that in a few days . |
Kool!
I tried to make 1 with a polarizing reflector and 1/4 wave retarder plate in front of a first surface mirror.
Idea was the light of the right polarity goes through to the LCD. Light with wrong polarity is reflected, turned 90deg, hits the mirror, turned 90deg and goes to the LCD with the right polarity!
Great!
Only problem is the 1/4 wave retarders only work at specific light frequencies so you need 1 for red, 1 for blue , 1 for green which is damned expensive. Also all these layers absorb a bit so you dont gain that much. I torpedo'd it.
I'd love to hear your solution. |
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| Hezz |
Guys,
I hate to admit it but one thing you should be aware of and Rox is right about this, is that the laser test will not give you the correct FOV. It will only tell you the maximum angle that the lens system can pass light through it.
The problem with the laser method is that it is only one wavelength of light. Or at least a very narrow band. The FOV is the angle where at least three critical light wavelengths for daylight have been corrected for. The FOV is where the correction has been made to a designed standard where the spot sizes of these three wavelengths are sufficiently small and aligned to be considered acceptable performance for the intended application.
The lens will still image to a lesser degree outside of the FOV.
Now it would not surprise me based on the cost of this lens that it only has a 24 total angle FOV like Rox claims the manufacturer has said. The lens was probably cobbled together from existing stock lenses to make it cheap. This would explain why the edge blurriness is a problem and the only way to deal with it would be to reduce the corner to corner distance of the LCD by using a 4:3 aspect ratio or smaller LCD.
That being said we must as Guy said put things into perspective. THis is the best lens for a 17 inch LCD for a low cost that we have at the present time. And we in all likelihood will have to get by with it until someone can get a manufacturer to have a fully optimized large format triplet made. This will cost a lot more. The last quote that someone got out of India was about 500 - 600 USD per lens for at least 100 quantity.
Rox,
If you use a high quality 10 or 12 inch LCD with this lens you should have a lot less edge problems.
I would rather live with the edge problems until I can get a better lens either by making it by hand or something else.
Hezz |
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| Rox |
| quote: | Originally posted by Hezz
The problem with the laser method is that it is only one wavelength of light. Or at least a very narrow band. The FOV is the angle where at least three critical light wavelengths for daylight have been corrected for. The FOV is where the correction has been made to a designed standard where the spot sizes of these three wavelengths are sufficiently small and aligned to be considered acceptable performance for the intended application.
Rox,
If you use a high quality 10 or 12 inch LCD with this lens you should have a lot less edge problems.
I would rather live with the edge problems until I can get a better lens either by making it by hand or something else.
Hezz |
THANKS!!!!! (I really thank that at least one of the menbers here agree in some litle point with me) thanks for this hezz.
I agree with you. I think tis lens is a good choice for our setups yet. But WE HAVE TO ASSUME SOME LIMITATIONS THAT MOSTLY CAME FROM THE TRIPLET ITSFELF, NOT FROM THE FIELD FRESNLELL AS WOULD BE THE UNFOCUSED CORNERS AND A MAXIMAL THROW SO THIS DISTORTIONS KEEP UNDER ACCEPTABLE VALUES).
I have been well maneredly kicked from a popular forum right now (my rights have been suddenly dropped to a point where i canīt even post replys, this is a well maered way for me :d)
Thisis right now the only forum where the information canīt be delted if the owner doesnīt like it. Actually I understand that if someone sells an item, doesnīt like to read it isnīt the correct item for the setup on his own forum. But I donīt like people being cheated. I really started myinvestigation for me, but then thought this information is very usefull for the comunity.
just let me tell you that i would say 80 triplet would do similar work with 17" or even better than 135 triplet. Thats because the fov on the 80 triplet is much larger than the 135's. (but the bad side of the 80's is the aperture, this is obyously better on the 135)
Finally let me tell you that it was me the most disgusted person when found this len's field angle.
anyway my challenge is open yet for you that try a setup with 135.
http://www.diyaudio.com/forums/show...?threadid=55209
I really thank you verymuch hezz. Have a good day. |
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| Rox |
now here comes the one millon question;
we have told to 3dlens our ideal fresnell lens. This lens was bassed on 135 triplet and a 100" image. A thing that it has not been checked/demostrated yet. Do we agree with this setup now? mean is the 550 fresnell our ideal fresnell lens?
this was a present from the 3dlens owner, and i start thinking we did things too fast. Please what do you think about? |
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| Hezz |
ROX,
Something you should know about the 80 mm lens. I had that lens and tested it and even though it has claimed wider FOV it does not have as good an image as the 135 mm with a 15 inch test image and given the same light illumination.
Meaning that it is designed to an even lower standard of resolution.
But in the end both lenses will work and what you should really be thinking about is where your projector will be placed and how big the image is. This will determine what focal length lens that you need.
For me the 327 mm FL will not work as I need 450 - 500 mm FL.
Hezz |
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| charlie10 |
| quote: | I tried to make 1 with a polarizing reflector and 1/4 wave retarder plate in front of a first surface mirror.
Idea was the light of the right polarity goes through to the LCD. Light with wrong polarity is reflected, turned 90deg, hits the mirror, turned 90deg and goes to the LCD with the right polarity!
Great!
Only problem is the 1/4 wave retarders only work at specific light frequencies so you need 1 for red, 1 for blue , 1 for green which is damned expensive. Also all these layers absorb a bit so you dont gain that much. I torpedo'd it.
I'd love to hear your solution. |
Light recycling: slightly off-topic, but I haven't seen it discussed recently. I'm very happy to since I'm in the middle of tinkering with this. I've obtained a few 3M Vikuiti film samples (DRPF, DBEF), unfortunately all are "diffuse" since that's appropriate for wide-angle LCD backlights. Do they have one that's totally clear / non-diffuse? I guess I should ask my contact there, but wondering if anyone here had experience.
Also obtained a quarter-wave retarder sample. Yes there is a peak wavelength, my sample is 440nm but I think it would still do an ok job of the reds and blues? I'm having a hard time lining up all the fast axes though! I barely even know what a fast axis is. Is there a good thread to discuss this on? I'd love to hear more about your results me2.
c |
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| Rox |
| quote: | Originally posted by Hezz
ROX,
But in the end both lenses will work and what you should really be thinking about is where your projector will be placed and how big the image is. This will determine what focal length lens that you need |
yes i agree that image size and throw is the most important spec to check in our designs. But we shouldnīt forget about the field angle like have been done untill now. this is the next most important thing for me.
Lets say i try to do a projector with 15" and 80mm slide projector lens. I work out the throw, image size.... and everything looks like it would work. The main problem if i do it would be the field angle from the triplet would be just projecting a 3" central image of my 15" lcd. Thats becaouse i didnīt take care of the field angle. |
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| jcbklyny |
| quote: | | and i start thinking we did things too fast. Please what do you think about? |
I think you should build a projector first. |
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| Rox |
it is you the first one who told me there are limitations with the throw with this lens.
And it is you as well te one that told me you got the triplet at 52cm from the lcd. If we add 20mm gap and say triplet optical center is at 6cm fartcer then you would use 2+52+6=600mm focal field. Donīt you think the 550 ideal is precipitated? |
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| Me2! |
| quote: | | Also obtained a quarter-wave retarder sample. Yes there is a peak wavelength, my sample is 440nm but I think it would still do an ok job of the reds and blues? I'm having a hard time lining up all the fast axes though! I barely even know what a fast axis is. Is there a good thread to discuss this on? I'd love to hear more about your results me2. |
The plate I got was for a red scanning laser. It was designed for ~700nm. Yes, everything goes a mild pink.
Yours might work in blue. 440nm is in the purple. Not sure why they gave you a sample for that region. Unless you mean 440labda? That would be red. Usually these things are fairly specific to the wavelength. YOu might have the best source because their stuff is designed for LCDs and might have multi-layered coatings already in. Did it come in multi sheets? I'll have to check out thei stuff. Let me know how yours turns out :) |
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