| tetutigre |
Hi,
I wanted to ask about what kind of lens would be comparable to my fujinon f1:1.2 lens. I'm looking for around 3'', and would like the lens to give me as much brightness as the fujinon gives me... which bring me to this question, does the less (f:x.xx) give me better brigthness?? I've found some camera lenses, but they are way expensive.... thanks in advance.:) |
|
|
| dnsey |
The f/ number represents the ratio of focal length to iris diameter, so yes, the smaller the number, the greater the light transmission.
You should be able to find a fairly cheap camera lens - look at M42 fitting ones - millions were made, and they're nearly obsolete now, so sell very inexpensively. |
|
|
| tetutigre |
Hi,
Thanks for the reply (at last I've got one right !!! :) ) I've been looking around Ebay and the ones I've found are either too small (50mm and below) or have F2.8.... again, I"m just looking for about 3'', I'm using one of those hipgear lcd's. Thanks |
|
|
| Guy Grotke |
I think the use of f numbers may be misleading when it comes to projection. With a camera, a lower f number means a lens captures a wider arc of the light coming from an object, so it gives you more light on the film. The focal length is included in this f number, because a longer focal length "looks at" the object from a longer distance. So a lens of a specific diameter will gather more light from a near object than another lens of the same diameter but a longer focal length will gather. The photographer uses different iris stops to make the lens effectively have higher f numbers, to enhance the depth of field. Or he can open the iris all the way to defocus things in other planes than the principle object.
But in a projector, all of the light comes from the condensor system. It is in a fixed size cone converging on the projection lens from the whole LCD surface. It would not matter if the lens had a wider diameter (thus a lower f number), since the light would not intersect the outer portions of the lens. In fact, the image would be sharpest if the light was all perfectly converged to a point just at the center of the projection lens. Then the lens would act like an f22+ pinhole, with great depth of field and no distortion at all.
So how wide does the lens have to be? Just a bit wider than your condensor can focus the light at the entrance pupil. Since we tend to use non-adjustable condensors, due to limited choice of fresnel focal lengths, your projector may need a wider lens than another projector with better condensor convergence. On the other hand, if your condensor system puts all the light at the center of the lens, then changing to a wider lens (with the same focal length) will make no difference at all in the image brightness. |
|
|
| tetutigre |
Thanks for the reply. :)
I was doing some testing last night, and came up with couple things... (BTW I"m using a 2.5" lcd and the backlight-still working on my light source) - projected distance 7ft.
- The Fujinon (145mm diameter, f1:1.2) gave me great brightness, sharpness and color; but the picture was reduced about 30''. The lens is right next to the lcd.
- a Bell & Howell 4" f:3.5 coated anastigmat gave me a bigger picture (I think about 50''), but reduced brightness, kinda hard to see at times. The lens is about 1.5-2" from lcd.
- an opaque projector lens (no idea on measurements) gave a reduced picture and had it far from the lcd - so no useable.
Is there a way to find a lens that gives me a nice balance? Thanks for all your help. |
|
|
| Guy Grotke |
With a 2.5 inch LCD, what you are building is more like a slide projector than a larger-format LCD projector. For the larger format designs we use fresnels to make the light converge toward the projection lens. For your design, your lenses are probably already capturing all the light going through the LCD since they are larger than the LCD. So you don't really need any fresnel condensors.
I think the difference in brightness between your lenses, is just the difference in image size. If you moved the projector back until the Fujinon gave you a 50" image, I bet it would be about the same brightness as the Bell & Howell 50" image. It is just a matter of spreading the same amount of light over more area, so you get fewer lumens per square inch.
I think you need a better lamp! |
|
|
| tetutigre |
Thanks for your input on the lexan and the fl lens issue in both threads. You da man !!! :cool:
Regarding my lamp choice..... there are some reasons why I'm going this route. 1) I don't have $200 for a 250w HQI set (yet), and these bulbs are rather cheap. 2) I wanna start with a small setup -this bulbs are small, and the Mh ones are big, sometimes huge + ballast and all that. Again, this is a small screen, so my thoughts are that it might not need as much dispersed light as other setups do -and don't wanna fry the lcd. 3) I've seen other setups that use small dichroic lamps, so I thought I'd give it a try.
I'm trying to keep the setup small, and by having a parallel setup would be easier and smaller: my thoughts were: lamp-lexan-lcd-lens... but I think it would be something like: lamp-heat glass-lexan-lcd-lens... or: lamp-cold mirror-lexan-lcd-lens. Does that make sense? :confused:
It's my first step in actually building a DIY projector --> moving from the OHP route (too big). And my dream is that I'll be able to use my projector during daylight (of course not possible with the dichroic lamps). And if this projector works out, I'll be more motivated to move up. Thanks for all the help, and don't stop giving out such grealty needed support !! Thanks.
:D |
|
|
| dnsey |
Guy, I have to disagree with your analysis of the importance of aperture.
If you are correct, why have 35mm projectors almost always had f/2.8 or wider lenses, even when these were difficult to calculate and expensive to produce?
Indeed, why not use an actual pinhole, which, if carefully made in suitable material, is capable of very respectable results, and costs *much* less than a decent lens.
I have seen a top quality, high transmission factor, 35mm movie projection lens with a front element around 14" diameter - that's an expensive lens! If your theory worked, wouldn't it be a lot easier and cheaper to use, say, an f/8 lens, and pay careful attention to the condensers instead?
Even if you were correct, a multi-element lens has an optical centre (of sorts), but the size of the elements in front of and behind this point would still affect the transmission of the assembly. |
|
|
| ace3000_1 |
| quote: | | I don't have $200 for a 250w HQI set |
What? $200? where from? they are around 90euro in europe as a kit including the bulb.
Trev:) |
|
|
| Guy Grotke |
Here is a link to goodmart.com:
http://www.goodmart.com/products/Tu...Halide_Lamp.htm
They have a lot of less expensive bulbs and ballasts. For example, they have a 250 Watt bulb for $21.33 and matching ballast kit for $45.36 US, plus shipping.
These tend to be bulbs with the standard color temperature of 4200 K, but they certainly are cheap!
I don't think that you use a lower wattage lamp because you have a smaller LCD to illuminate. I think you need enough lumens per square foot of final image, so the LCD size is not as important as the final image size. But you may run into a heat problem when you try to get all of that light through a small LCD: Compare the area of a 2.5" LCD to the area of a 15" LCD. You would be putting 36 times as many lumens per square inch through your 2.5" LCD, compared to a 15" LCD, to get the same number of lumens on the screen.
Maybe you should just try for a smaller image. |
|
|
| tetutigre |
Hi,
The price I was quoting was a self aproximation of this + shipping. Thanks for the heads up about the prices...
About screen size.... I just wanna be able to project on my full lenticular screen (I think it's either 60'' or 70'') or on my 50''x50'' blackout cloth.
so, even if I used the cold mirror and the lexan, would I still be having heat problems (using fans also of course)? what about distances? I would like to keep my setup under 10''x6''x6''....
Thanks for your support guys !! It's really getting me pumped up, kinda like Hans and Frans.... SNL (never mind). :xeye: Please keep guiding me in the right direction fellers !!! |
|
|
| Guy Grotke |
The 4.75" diameter cold mirror I got from surplusshed.com for $5 works very well. I think you will not have a heat problem if you can reflect your light from one of these cold mirrors. Since you are trying to light a small LCD with a wide parallel beam, that size cold mirror should fit perfectly. Put a black metal heat sink an inch behind the cold mirror to absorb the short-wave IR and re-emit it as heat. The heat sink will get hot, so it needs some fan air.
With this design, you should be able to make a very small box: You have no condensor or lower fresnel, so you don't have to put the lamp at the lower fresnel focal length. And you are using a wide diameter slide projector lens with a very short back focal length, so you don't need to have space for an upper fresnel focal length, either. What you are making, is essentially a slide projector. It will not have to be any larger than a commercial unit, except you should have a long enough path from the lamp to the LCD so you can fit the 45 degree angle cold mirror. If the lamp beam spreads to be too large over than distance, then you could get a bit more light through the LCD by adding a very weak condensor lens to converge the cone of light a bit. You could try a lens from a pair of reading glasses for that, if you have access to some different strengths.
If you change to an omni-directional MH lamp at some time in the future, then you would want to add a spherical reflector and a condensor lens so you could get more light heading toward the LCD. |
|
|
| tetutigre |
"You could try a lens from a pair of reading glasses for that, if you have access to some different strengths."
you mean reading glasses like the ones you find at Walmart and such? What kind of strenght should I use for better brigthness?
another BIG concern that I have (BTW) is the LCD ribbon cable... I really don't wanna screw it... how do I do to keep it from tearing (reinforcing)?
Man, I'm learning so much !!! Thanks a lot !! |
|
|
| Guy Grotke |
Reading glasses are just a cheap way to find a weak positive meniscus lens of the right focal length. Especially if WalMart or the drug store will let you take them back or exchange them for another weaker or stronger pair. They are rated by Diopters, where:
Diopters = 1000 / focal length in mm
So a 1.0 Diopter lens has a focal length of 1000 mm. A 2.0 has a focal length of 500 mm, etc.
I suggested a weak positive lens, if the beam between your dicroic reflector lamp and the LCD is spreading too much. Putting the lens near the lamp would converge the beam. It would be acting as a weak condensor lens. A 1 Diopter lens would make a parallel beam focus on a point 1000 mm from the lens. So it will make a beam that is diverging two inches over 1 meter distance, into a parallel beam. You can see that this is not much refraction. Reading glasses come in many strengths from 1.0 up to 5.0, so that gives you a lot of different lenses to try for free!
Regarding the flexible printed connector cables, I would mount the LCD and the controller boards in a rigid frame, so those cables are held in one position without any stress. I made something like a picture frame out of aluminum and wood. The LCD fits into the frame and is held in place securely. The PC boards are flopped over about 150 degrees from their normal position behind the backlight. Then they are held against small angled blocks of wood with tiny screws and rubber washers. The flex cables are under no stress at all. The boards stand up less than 1" above the surface of the LCD.
For a design that uses fresnel lenses to converge light at the projector lens:
If you are planning to use a mirror after the LCD, or a split fresnel design, then you need to move the PC boards pretty much out of the way. With a mirror, the LCD will have light moving from the back to the front, and you have to get the lower fresnel tray close enough to the LCD. With a split fresnel design, you need fresnel trays on both side of the LCD and you don't want either tray hitting the PC boards. If you will not use a mirror and both fresnels will be under the LCD, then you could mount the PC boards at a 90 degree angle from their normal position, since the light will then go from front to back of the LCD.
But I have seen pictures of many LCD frames where the boards are flopped over 180 degrees and screwed down to the frame surface. The point is to get them all mounted securely as soon as possible, so you don't keep flexing the cables or accidently tear a cable off the LCD or board. |
|
|
| tetutigre |
"Putting the lens near the lamp would converge the beam"
Do you know how much heat do these lenses take? I'm afraid I'll make it explode if it's too close or has too much heat...
I am waitning on my cold mirror from surplus shed... I went ahead and got the hot mirror just to see how it works.
I think I'll have to hurry up with this... my OHP is acting weird... it burnt 2 lamps with no apparent reason!! I thought the lamp had died... so I chenged... and when I turned it on, it popped the inner coil... tried the other lamp... same thing. What wrong, the bulbs or the OHP??
Thanks !!! |
|
|
| Guy Grotke |
Good point. A glass lens would be much better than an acrylic lens for this! You could use either one for a quick experiment as I suggested, trying different strengths and taking them back for exchange at the store until you find the right strength. Once you know what lens you need, then you could get one that is made from glass, or even pyrex if it gets very hot. Reading glasses are just a good way to try a lot of different strength lenses at no cost, before you buy a real uncut round lens of the correct strength and size.
About those OHP bulbs that burned out immediately: Did you touch them with your bare fingers? Some bulbs (especially halogen) will pop if there is a fingerprint on the outer glass. The fingerprint absorbs so much heat that the outer glass expands unevenly and cracks. |
|
|
| tetutigre |
I don't think I touched it... I'm fairly careful with bulbs... I use them quite often for my classroom OHP, and never had this problem before... it seems like the coil just came loose... I mean, you shake it and it sounds like a rattle.... :clown:
I'll have to contact maintenance to check it or get a new one... but that's another story.
Also, you mentioned a black heatsink behind the cold mirror... does it have to be black? I've got a blue one... might work the same way, but just wanted to check with DA MASTER... :cool:
Thanks !! |
|
|
| Guy Grotke |
Thanks, but you give me way too much credit. Lots of other people on this forum have way more experience with projectors. I just report things I've tried or read about. A lot of it is from other engineering projects not connected with projectors.
A blue heatsink is probably okay too. Black just absorbs more energy. Flat black paint is good, but black anodized aluminum is better. The best is carbon black, but that can be messy. If your blue paint is shiny, you might want to sand it a bit to make it dull.
The point is: Don't put it right up against the back of the cold mirror. That would heat the mirror glass and make it emit long-wave IR out the front. Put the heatsink at least an inch beyond the back of the cold mirror, with some cooling air blowing between them. The heatsink will absorb the short-wave IR and that energy will be carried away by the cooling air. Then the cold mirror will stay "cold". |
|
|
| tetutigre |
You might be right, but newbies like us really appreciate the help of those that have the knowledge and are willing to put it in idiot-proof terms and share it with us, and not like others that are (or may think are) too cool for us and won't even bother, you know?
You said you worked for Conexant? I've recently got me a WinTV card, and it's got a conexant chip on it...
Thanks ! |
|
|
| tetutigre |
I got my cold & hot mirror on the mail yesterday... man, that's what I call fast shipping !!
Anyway, I did some more testing with 2 other lenses I bought. one is a dukane 3'' f4.5 (probably from a 16mm film projector), and the other is a kowa fl 112mm f4.5 copy lens.
I used an 4'' LCD monitor from my daughter's video set, so light source is the backlight. I used my lenticular screen at 70'' (56''x42'' which makes it 4:3).
Fujinon 145mm f1:1.2
lens right next to the lcd and covered 70'' at 100'' away -- After that it started to lose focus even with the screen right next to the lcd. Though it has the best brightness I've seen, pretty good for a backlight light source.
Kowa copy lens
lens was about 5 inches from the lcd and covered 70'' at 74'' away -- good focus and medium brightness, not as great as the fujinon.
Dukane film lens
lens was about 1.5'' from the lcd and covered 70'' at 64'' away. This one gave me the biggest icture with short throw. Then of course it's designed for a 3'', so it didn't cover all the lcd screen, but was impressed with the magnification power and the brigthness was decent.
Bell & Howell 4'' anastigmat f3.5
lense was about 1.5'' from lcd, and covered 70'' at 84'' away. Brigthness suffered with this one, but seems to be a pretty good and sturdy lens.
SO guys, which one would be the better choice? I'm thinking about using the dukane one... I'll definitely use the fujinon in another project with a biger lcd like the one with leds... what factor should I take into account before starting out? light output, how far from screen it'll be..... I'll be putting more time on it as soon as I'm done with all this workload (final projects, term papers, final exams, etc, etc etc.... :smash: :smash: :smash:
:confused: I need your input here, thanks in advance.
P.S. BTW, the screen was not of great quality or resolution, however, the screendoor was not greatly noticeable... would it be the projecting size or the screen? |
|
|
| Guy Grotke |
I think you are in an ideal position: You already have all of those lenses, so you can try them all once you have your lamp/heat filter/LCD/fan assembled.
The only suggestion I have is to make sure that all of the light is actually making it to each of the lenses. A large diameter lens that has a very short focal length will be close enough to the LCD to capture all the light coming through from your parabolic reflector lamp. But some of the smaller diameter or longer fl lenses may not intersect the entire cone of light diverging from the LCD. For those lenses, it might help to add a weak condensor lens just under the LCD to get the light converging toward the projector lens.
If you can see screendoor, then you have two things present: Enough magnification to make it visible, and a very sharp focus. Every LCD made has a screendoor-like structure, because there are conductive metal traces between each dot of liquid crystal material. You can just ignore it, since you will probably be sitting far enough away not to see it. Or go with a smaller image. Some people are so bothered by it that they purposefully defocus a bit to get rid of it. That seems kind of silly to me. |
|
|
| tetutigre |
NOw that I remember... the slide projector where I got the anastigmat lens for had 2 lenses... I think one was a small consendor right after the lamp, and then a double convex lens... kinda like
reflector -- bulb -- condensor -- double convex -- slide copartment -- lens.
I bet I could use them in this design if I don't get all the light... I'd just had to try to get it off the projector (it's one of those old ones made or very sturdy steel and stuff...) |
|
|
| tetutigre |
| another pic... sorry for the bad picture, my camera is not the best... but I hope the labels give you a better idea of the stuff. |
|
|
| tetutigre |
I can't get it to work right !!!! @#$@$#%@#$ !!!!
Ok so I got some spare time, so I decided to get everything setup for experiments... made the lcd frame, got the lamp holder, the mirror, etc.... but I can't get it to work right !! First, it's pretty hard to get the mirror at a right angle... then I try testing it with different lenses and the give me about a bright circle, and the corners are either cutoff or not lit at all !!! And I've still got light leakage... I then mounted one of those magnification things for gameboy, and there was more light, but still had those corners cutoff.
What I don't get is why there are dark spot, if all the light should be going through the tiny 2.6'' screen... would it be the lenses' fault? (I guess all this is my fault after all... :cannotbe: )
Guy, or even ace, could you help me out !?!? Man, I was SOO frustrated I thought about quitting... then I realized everybody has to start from something, and there is not better learning than experiencing things hands-on sometimes... but it's always better with a little help from my friends...
I need some help !!! Thanks in advance fellers !!! |
|
|
| Guy Grotke |
It could be that your LCD is just too big for the lenses, if they are all designed for 35 mm slides.
Start by troubleshooting the light path:
1. Put a piece of white paper at the surface of the LCD that faces the light. Is it evenly lit, from corner to corner? If not, then adjust your light until it is.
2. Put a piece of white paper on the back surface of your projection lens. Is all of the light coming through the LCD falling on the lens?
3. If those are both okay, then try using a big magnifying glass as your projection lens. Measure the focal length using the sun. Put the lens at a bit more than the focal length from the LCD, then move it back and forth until you get a focussed image. (Screen must be at least a few feet away.) Does that give you an image with the corners lit? |
|
|
| tetutigre |
Ok so I did my tests again. :rolleyes:
Bulb facing the cold mirror, moved it until I found a circle that covers the lcd with a piece of paper... it seemed to cover all of it.
The I checked with the piece of paper after the lcd... I could see the square and the unfocused image...
Then I tried with the lenses... but still giving me dark corners... tried adjusting color, brightness and contrast but still the same...
Then I changed the light path, got my hot mirror and set it in front of my bulb (BTW, I set the cold mirror behing a plastic support while I was doing my test - bad idea, when I removed the plastic it've been starting to soften up !!! - :bigeyes: ) ...
Then I went to find my page magnifier... I could not find it - but I did find a frsnel from a non working OHP, so I popped it at about 7'' from the lcd.... and VOILA !!! a super bright and almost clear picture, all corners lit, but of course not as big as with the lenses.... but I couldn't believe my eyes !! I had the screen at about 50'' or 60'' away from the fresnel and I got a 30'' image, almost clear (considering it's a fresnel). the I turned all the lights on in the room and living room, and the image was very watchable... :bigeyes: :bigeyes:
Then I thought about projecting further... so I moved the screen at about 170'' away from the fresnel... and got a bright 60'' image, turned the lights on, still very watchable... :bigeyes: :bigeyes: :bigeyes:
At first I was trying with cartoon finding nemo, but then I moved on to The terminal, but still the image was great (you could not see all the details in the barckground, but you could see almost everything, specially close-ups). :bigeyes: :bigeyes: :bigeyes: :bigeyes:
Some additional information: I'm using a lenticular screen (I guess that helps make it watchable with lights on), and also, with the bulb and hot mirror, if I put my hand in front of it, I could still feel heat, but the lcd never got warm... this was without a fan (I will surely use one).The hot mirror was virtually right next to the buld (maybe couple mm in between).
OK..... now to draw some sort of conclusion... where do I go from here? If I stick to this design the projector might be awful long, but at least I know it works... I'm afraid light output will be affected if I used a FS mirror (comments on this)... and should I keep the fresnel as my objective lens?? The fresnel if designed for an OHP so it's awful big, and I would have to cut it down to fit... how do I do that? And also, I think I can get a hold of a thicker fresnel that would produce better quality... am I onto something?
So many questions... and to think that I was ready to quit and give up.... NO WAY JOSE ! :D
Thanks in advance for all your help !!! Keep the ball rollin' !! :) |
|
|
| Guy Grotke |
If you are happy with the image size and throw distance, then I think the next step would be to replace the projection fresnel lens with a PCX (good) or positive meniscus (better) lens of the same focal length. You only have an image field angle of 20.3%, which either lens type should do well. If you don't know the focal length of the fresnel, take it out around noon and measure the distance to the smallest image you can make of the sun. Don't buy a shorter focal length PCX or positive meniscus: If you want a larger field angle, you will need to go to a duplet or triplet lens.
A glass lens should be sharper and not have as much loss as a fresnel, but you might want to experiment with a stop aperature on the fresnel before you decide what size lens to buy. Cut a 100 mm diameter circle in a piece of cardboard and use that to cover the fresnel. If most of the light is hitting the hole, then the image will not get much dimmer. If it does get a lot dimmer, then you will need to add some focussing using a condensor system to get the light pointed toward the center of the lens. |
|
|
| tetutigre |
Ok, got some pictures to show the setup. I took them last night, got the setup running for about an hour or longer, and had no heat problems (I think/hope). they are not the best but I'll try to explain them.
This first one shows the setup (is not enclosed, and gives you a vague idea of what I'm working with so far. |
|
|
| tetutigre |
| Another one of the setup |
|
|
| tetutigre |
| Here is another picture with the results. It was projecting a 35'', very bright, not prefect, but good enough for this screen's resolution. |
|
|
| tetutigre |
| One more, with the LIGHTS ON. The projection is actually brighter than it seems (thanks to the lenticular screen). The cloth on top of the screen is blackout cloth that I used for some testing... the colors are a little little better with it, but cannot see anything with lights on. |
|
|
| tetutigre |
The bottom line....
It is great to have a bright and decent picture, but I am not happy with the image size and throw distance... unles there was no other way for me to go. SOOO, I would like to find a lens that does the job the fresnel is doing, but with a bigger image at about the same throw or less... so should I look for a lens with bigger barrel to cover the whole lcd? BTW, I found my page magnifier, put it on front of lcd... had to go WAY far from the lcd, and projected a smal, blurry image... so much for the 100'' scam!
For the PCX lens, I have one from the gutted OHP I used the frsnel from... I'll try some testing with it tonight.
Christmas break is coming and that means more time to experiment. BTW, I was able to find a 250w MH setup for $50... I will try to use that to rtrofit an OHP... anyway, I'll keep working !!
One last picture. Movie: The terminal - widescreen. Lights on. Viewable Size: 35'' Experience so far: Pricele$$ |
|
|
| Guy Grotke |
From the images of your setup, it looks like the light is spreading out from the LCD. The big fresnel collects a lot of that light. If you just stick a smaller glass lens in there instead, it will only collect a small part of that light. I would say you have two options:
1. Get a CRT projection lens that is bigger than your LCD, and has to be put very close to the LCD. That will collect most of the light.
2. Put one or two fresnels an inch before the LCD to converge the light to a triplet. Some of the DIY sites sell triplets for as low as $29. |
|
|
| tetutigre |
Thanks Guy for following this thread and keeping an eye on me. I really appreciate it.
Ok, did more testing. I finally got my 70'' projection... but the projector was at about 200'' from the screen... that's about 16 feet. But the picture was still bright, even with lights on.
Is the lenses on OHP's PCX? If so I think it is not going to work.. I tried mine and it had to be far away to show the picture, and it was small... of course OHP use mirrors and all.... what's your comment on it?
About the light leaking out, my thoughts are that since it's not enclosed I might be losing a lot of light, but once I enclose the unit the problem will be solved somewhat. And of course I would have to cut the fresnel to fit.
About other lenses, let me throw you some links to see which one would work better in your opinion...
http://www.surplusshed.com/pages/item/l3077.html
http://www.surplusshed.com/pages/item/l2006d.html
http://www.surplusshed.com/pages/item/l3132.html
http://www.surplusshed.com/pages/item/l3290.html
http://www.sciplus.com/category.cfm?subsection=21
http://www.goldmine-elec-products.c...s.asp?dept=1096
I've got a fujinon projection tv lens (145mm diameter) which I've comment on before, but the thing with this is that it has to be right next to the lcd, and not sure if I can get the controller board out of the way (more than 90 degrees)...
Will keep experimenting, that's for sure. I'll get a hold of the other fresnel today, and will try to run test during daytime. Hope to hear from you soon. Thanks !! |
|
|
| Guy Grotke |
OHPs use either a triplet, or a symmetrical duplet. Either one should work with your LCD, but if you take apart a symmetric duplet that is (lens mirror lens), then you need to put both lenses in a tube with the same spacing as the original setup. If there was a stop aperature, or the mirror was smaller than the lens diameters, then you need to add a stop aperature midway between the lenses. Otherwise you get a bright middle and dim edges. The lenses in a symmetrical duplet are either PCX or positive meniscus. Don't try to use just one lens, since that would have about half the focal length of the pair together.
I think your choices are clear: Either go with the Fujinon CRT lens by moving your controller board a bit more, or add some fresnels behind the LCD as a condensor system to get all the light pointing into something like your Kowa copy lens. Using a fresnel as the projection lens will never work well. You alread got both of these lenses to work, now you just need to adjust things to get one of them to work well. |
|
|
| tetutigre |
Hi,
The OH lens is a singlet.... I tried with the mirror but did not get good results. :(
I gutted out the lenses from the slide projector - one is a double convex, about 2.5'' diameter, the other is a small condenser that was placed right after the bulb to collect the light. Anyway, I put the convex in front of the lcd and got a big image but it was hard to focus... put is behind the LCD and the light output incresed a bit- but not too much. Then I tried the condenser, about the same results. :xeye:
I got a hold of the other fresnel, from an Apollo 2210, it is thick and both sides of it are soft, no ridges... so I'm thinking there are 2 fresnels glued together or something... this increased brightness a little, but not a whole lot compared to the other fresnel (from a 3M 9050).
Do you know if there are any CRT lenses that are smaller than the average ones? The one I have is huge compared to the tiny screen I have... or I could try to find a lens that is big enough to cover the entire LCD... I saw a lens on Ebay from a kodak slide projector that cover 7'' or so... I wonder if that would work better than the ones I have... :xeye:
another question I have: I went to Lowes and they had this 50w 12v dichroic bulb with a 15 degree beam and UV stop... is it any good for what I'm trying to set up?
Thanks for your help. |
|
|
| Guy Grotke |
>CRT lenses that are smaller
I guess you could ask the electronics goldmine website the diameter of their TV projection lens. If that is smaller, it might work for you. I think they come in a lot of different sizes.
>50 Watt dichroic bulb
Dichroic reflectors are great, and a 15 degree beam would let you use a single lens to converge the light to the projection lens. Or maybe with a large enough lens, you wouldn't need to converge it at all. But you need a certain number of lumens per square foot of screen image, not LCD area. If you want a 70" image, then I doubt that any 50 Watt halogen bulb will do it. Maybe the "Philips 100 Watt wide pin capsule bulb with a GY8.6 base", would be bright enough if you add a good spherical reflector behind it and a condensor lens in front of it.
I have seen some pictures of a projector where the builder used an abrasive cutting wheel to remove the base of a large dichroic reflector halogen bulb. Then he put a very small MH lamp in through the hole, to make a super projection lamp. But I think you could get just as much light out of that MH bulb with a silver-plated soup ladle behind it. Then put a hot mirror in front of it to remove the IR. |
|
|
| tetutigre |
Hey how do you read my thoughts !?!?!?! :bigeyes: I was thinking about that bulb when I saw it the other day... and was also wondering if it would fit in a dichroic-type reflector...
I found this interesting contraption that I might experiment with... don't even know what it is, but it has bulb and lenses for $3, so I might as well give it a try...
It's sunny today (cold though - lucky you in CA), so I'll run some testing during daylight.
Thanks !!!
BTW, do you have any idea of what to do with a 48'' fresnel?? :clown: |
|
|
| Guy Grotke |
Maybe melt aluminum for doing casting? Actually, you don't have to put stuff exactly at the focal length. So you could make a solar furnace that would heat stuff as much as you wanted by adjusting the position.
I knew the specs of that halogen bulb because I have one sitting right next to my computer. I bought it to use for adjusting the optics spacing in my projector, since halogen is much better at on/off cycles than MH bulbs. |
|
|
| tetutigre |
My lcd screen does not show anything at all. There was an unfortunate accident involving my daughter and it seems to not work at all... :faint: Right after the incident I connected it and seemed to be ok, but later I tried to make it work but nothing.... :bawling:
I was hoping to make a DIY RPTV with that fresnel...
:redhot: @#%#$%# I'm so P#$%^%$@@#D... :redhot: I've put so much effort on it, and now it's all screwed. Everywhere seems to be out of good-priced tiny lcd's... and don't have the $40+ bucks for another one... :ashamed:
Thanks Guy for hanging out and helping me throughout this journey... I guess it's back to the bulky dim OHP setup. :worried:
Adios |
|
|
| ancorp |
Ive been following this thread abit -- and that was an unexpected conclusion:( :( :( !!!
Dont give up man!:whazzat: Check the wiring inside, something could have ripped off!
Keep calm though:rolleyes: |
|
|
| Guy Grotke |
That's a shame. These panels are so fragile once you strip them. That might be a good argument for repackaging them in a frame with Lexan on both sides, just to make them at least as damage resistant as an OHP LCD panel. I keep envisioning having the projection lens fall back into the box and right through the LCD! At least they don't explode into a million sharp fragments, like a CRT.
Must be an unlucky day for Projector DIYers: I just sliced the top of my thumb with a razor knife while I was cutting out rings from a mailing tube, to make a symmetrical duplet. (I'm usually smart enough to cut AWAY from my hands!) Fortunately it was a new blade (and so pretty clean), and I got the bleeding stopped with a few minutes of pressure. A big bandage and a little Ibupropen later, it doesn't even hurt anymore, but it will slow me down on my projector building.
Does anybody have a spare small LCD left over after an upgrade, that needs a good home? An old PS1 gathering dust? |
|
|
| tetutigre |
It was a depressing time last night not being able to do anything or experiment.... I don't like wasting money, and I felt bad that I had...
Now before I go on I've got a shoutout for Ancorp,
Thanks for your advice. I was really mad... so instead of taking my fury with the lcd, I decided to take it with the intergalactic creatures in Halo.... great therapy !! :cool: I kicked some buttae !!!
Ok, so after having that out of my system and getting some sleep I went back and tried to see what was wrong with it... I plugged it in and nothing happened... but then I remember that before, -at times- I would get burned by a little cable that used to connect the backlight and which I did not cut completely... so, I brought the lcd today to work and checked it out... I plugged everything in, but no burn :scratch2: ... and I purposedly tried to get burned (it's just a tiny little shock, nothing serious) but no burn... moved the switch back and forth... still no burn.
So now my thoughts are: either (1)my power cable need better welding (thanks to my GREAT soldering iron skills :cannotbe: ) or (2)the board is fried (which I know nothing about electronics and how to troubleshoot)...
So I'll go back home today and re-weld it... keep your fingers crossed !!!! :xfingers:
P.S. Guy, I hope your' doing better...
Ancorp, do you think I should still be ok with that RPTV? I think I' might call the person up and make him an offer or something... |
|
|
| ancorp |
Guy Grotke,
Sorry to hear that - that sucks, lol! Glad you got back on your feet quickly!
Tetutigre,
Hmmm, Virtual anger management, lol!
Keep at it, there are good chances of the LCD powering up!
I too got shocked by the damn transformer near the backlight plug.
The RPTV sounds like a half-decent deal to me - but see if you can test it first, perhaps it works ok, could use abit of tweaking thats all... than $50 is a great deal! BTW, try getting it for less, start at 20... than say 28, thats all you got... if the person wants more, tell him, fine i guess i can borrow 10 from someone... lol you get the idea... Good luck! |
|
|
| Guy Grotke |
If you are getting shocked from the backlight circuit, you should put some tape on the wires, or some insulation on the terminals. Radio Shack or any electronics store has brush-on paint for this, but you can also use silicone RTV or clear fingernail polish.
This is not just for your sake: When you get such a shock your fingers could carry the high voltage to other parts of the board and fry some delicate CMOS chips! |
|
|
| tetutigre |
OK, so I checked it again... re-welded (is that the correct verb) the power supply cable and check all connections... but still no power to anything, no shock or burn... I looked at the controller boards but there was nothing that seemed burnt or anything...
so now my question is, Guy, I know you work for Conexant, and probably know a bit about chip and stuff... could it be possible for me to send you the screen and maybe you can check it out and see what is wrong, or what I'm doing wrong? And I also have another screen that I could use, but there is no pinout for the power supply or video... it's only pins like the ones in computer and backlights... if you could help me with the both I would REALLY appreciate it. -or even just with one.
Ancorp,
I decided to back out on the RPTV. The lowest was $50; I also got some words from other people that the seller is not very trustworthy and stuff... and most important, I don't have room at all !!! I mean, if it worked I could find a place, but if it didin't I wouldn't have anywhere to put it to sit and collect dust while I try to find my way into this projection stuff. On a side note, could you draw a diagram on where your RPTV componets are located, where the fresnel is, and the screen, mirror, etc...
Fingernail polish ??? who would've thought.... :xeye: |
|
|
| ancorp |
| Here you go... I think its right, not sure about the order of sheets on the screen... I know the lenticular is in the front... |
|
|
| Guy Grotke |
tetutigre:
I write chip test software for them, but I have done some simple board design. If you have no other hope, I am willing to look at your busted LCD. I see that neither one of us has published our email addresses. You can contact me by phone (figure out how!), or maybe we can both send our email addresses to ancorp.
ancorp:
May we use you to exchange email addresses?
Thanks,
Guy |
|
|
| tetutigre |
OK, I think I did it right, changed my member preferences to show the e-mail thing. Hope it works.
Guy,
Thanks for being willing to help me out, I am clueless about all this... since my only DIY experience was to flop my Telex Magnabyte on top of my OHP (not DIY really). I hope the hip lcd works just because of the simplicity of things involved in the projector I guess. And the space of course. Of course if you can help me get the other lcd (5.6'') on track,I could use a CRT lens and stuff... :rolleyes: all those wishes...
can you tell it's Christmas ?!?!? :xmastree: LOL
Ancorp,
The fresnel is 38'' x 29'' (4:3) -found it at our local thrift store. It's got scrathes, but it's in overall good condition. How big is the FS mirror in your RPTV? how's the alignment accomplished? I tried using my tv with it, and it magnified it, but the further away it was it started to see ghosting... but now can you project something onto the FS mirror and the straight into the fresnell and make it bigger?? would that work, or is it how it works? Just wondering...
Thanks fellers !!!
______________________________
Jesus is the reason for Christmas. |
|
|
| ancorp |
Tetutigre,
I dont know the mirror dimentions - didnt measure it, and the tv is closed up... Its shaped like a trapezoid (is that the right word?)
The top is about as wide as the screen, the bottom is about 5-10 inches shorter...
The CRT's in a projection tv (or DLP/LCD projector if you wish) focuses through the projection lenses, the projection light path folded by the FS mirror, bounced off onto the screen. The fresnel is ontop of the screen is to push the light towards the viewer, help reject ambient light. On top of that there is a lenticular sheet that I belive adds alot more horizontal viewing angle. My theory - but probably the real theory behind RPTVs...
"hows the alignment accomplished?" alighnment of what, the mirror or the CRTs (convergence?) |
|
|
| tetutigre |
I was talking about the alignment of the mirror in respect to the projector and the screen... covergence only applies to the crt tubes I believe. I just wanted to check and see what was the alignment like - from the projected image onto the mirror and bounced to the fresnel focal point (I think)... now, what do you think if I projected a TV's image to that path... would it be something doable, or would I need your kind of triplet? Just wondering again... and wandering. LOL :angel: Now if I could get a hold of a lenticular sheet.... :trapper:
Do you have any resolution issues in yours? I remember seeing some RPTV up close and they didn't seem to have a sharp image... or maybe it's just me. |
|
|
| ancorp |
Lol, I have no idea about what focal points its at...
"what do you think if I projected a TV's image to that path... would it be something doable, or would I need your kind of triplet?"
you mean if you projected a tv set onto your big fresnel, and have a mirror along the path? You cant project onto the fresnel, it will just magnify the image more, i.e. it will become part of the objective lens, whatever you point the whole thing at, thats what it will project on. If you want to project like in an RPTV, you will need the actual screen as far as I know, the fresnel is just to direct the light towards the viewer... Or em I not getting this right?:xeye:
CRT projectors generally have a much more smoother image when compared to the fixed pixel field (dlp/lcd) projectors. My RPTV is only 480i, but at 640x480 on Svideo, my computer is usable! |
|
|
| tetutigre |
I thought I had already posted... mmmmmm that's weird. Anyway, I'm attaching the picture of the fresnel so you get an idea of it. I remember having one of those tv screen magnifier (they still sell them for older people with vision problems and stuff I think) ith turns a 19'' tv to a 26''... of course the viewing angle was limited, you could not see it from the sides and stuff.
Now, about the brightness... a crt or lcd projector are way brighter than a tv, but would it work ok in those conditions (enclosed, short distance)?? Just wondering again.
Guy,
could you please contact me to get your address and ship the lcd's ??? I've got the e-mail thing setup on the forum, but if it doesn't work, the e-mail is my screen name, @ yahoo. Thanks again for being willing to help me out !! |
|
|
|
