I wish mate, been busy doing other things lol, im going on a holiday soon though 🙂. My projector will be finnished this year aswell 😱, all on paper just a matter to find the time to build it now.
Trev🙂
Trev🙂
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 don´t understand it. I think the manufacturers don´t 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)
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 don´t understand it. I think the manufacturers don´t know exactly what am i asking for.
Thats what they told me;
An externally hosted image should be here but it was not working when we last tested it.
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)
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🙂
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🙂
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.
It sounds like that if you have the correct field fresnel, corner to corner focus and light distrobution should be possible.
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?
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?
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?
it is not compatible with only one focal and one magnification and one throw, you you understand it?
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🙂
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 🙂
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 😀)
Rox, still on it.
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 😀)
Rox, still on it.
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🙂
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 won´t 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 😀)
this dual field angle is very confussing. I don´t think it is that way.
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 won´t 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 😀)
this dual field angle is very confussing. I don´t think it is that way.
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🙂
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🙂
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.
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.
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 
Trev🙂
Trev🙂
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.
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.
ace3000_1 said: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
Trev🙂
how did you measured it?
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🙂
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🙂
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. 😀 Guess I was way off
So are you telling us that the information from the manufacturer is more than likely correct?
Rox,
That kind of make sense.. I think. 😀 Guess I was way off
ace3000_1 said:
mmm, i thought you did this way. let me tell you i did this test as well. I´ll tell you my results but first lets coment something;
"before the image distors" thats so relative..... i don´t think we can conclude a field angle. In fact i don´t 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 don´t know so i can´t determine one.
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