Custom Lens Design

Alright I want to build a lens. The ones we have are crap! I have bought the standard at LL and the 135 from diyprojectorcompany and both just dont work well. The LL looks great but way to short of a throw, and no way to work with 17" lcds. The 135 sucks *** all together after being told it would work with a 15-17 I find it will only view a 12" diameter or something like that so it really wont focus a entire 15 screen even.

Some have modified the 135 and increased the FOV but have lost contrast and clarity something that I dont really think is worth the time. I want to build my own lens? Why not someone on this forum has to know what elements we could get together to build the perfect triplet. There are alot of you out there that have programs to design triplets so what are the elements or lenses that would be needed to make one for a long throw and a 17" lens? I work for an optical company I dont mind some trial and error I can get them cheap we can get one started I get free ar coating granted that wont work for everyone but if we can get one to work then everyone doesnt need the trial and error, and it would be cheaper isnt this the goal or is everyone hear just trying to be the first to figure something out and make money off of selling crap that doesnt work?

I know there are some awfully smart people here and have seen some of the things people have done here they are amazing this isnt any harder, I dont have a 1000 dollar lens program to tell me what lenses are needed and even if I did wouldnt know how to use it. If you have a design or specs for a custom built lens this is the place to put your 2 cents I have heard of duplets that work decent also if you think you have an idea post it this is something that can be figured out there shouldnt be 1-2 people working on it and the rest of us waiting I am sick of waiting with no news and only dissapointment a bunch of us should be able to do this.
 
it would be easier to find out what I need? I dont see diameter as being the big problem everyone is looking for these large format lenses why is it that LL triplet can work on a 15? I dont understand lenses that well but what is it that I need to find what material is needed? Then I can go ask what is available, right now I tell them I want a lens and they just look at me like what type? we do primarily eye glasses but they also do other things I know they have a big military account too?
 

Rox

Member
2004-07-25 10:06 pm
?
by now, please ask about the largest lens you can get. Larger the lens, more light will capture and brighter will be the image.

before we go to a further details, you need somethimng like this:

1) 30cm focal "bestform" (this is biconvex but somewhere 1/3 diference of radius)

2) -15cm (negative) focal biconcave (near to simetrical)

3) 32cm focal "bestform" (bicovex again but 1/3 radius rate)

i thnk this is a good starting point for you. Let me know what's the larges lens you can use there at your job ok?
 
ok the largest lens that we have on hand are only the 80mm diameter while this isnt that big I think there is more of a possiblity to this then others. for starters the LL triplet is 60 some mm not 80 and the rear element is even smaller I think, and this works with a 15in lcd. Now I can get bigger but it would have to be ordered. Now we carry the cr-39, poly, high index, and reg glass, I think I can order other types if needed. I also can get ar coating done at our lab, and any 80mm or smaller lens, we also have these coatings http://www.essilor.com/Products/productsbrands.htm
if any are better I noticed the nikon one before which has a wierd reflective tint to it so not sure if it will work? I will ask tomarrow about the specs you said earlier dont think it will be a problem though? well see.
some questions

what is the optimal diameter I can see if I can get it?
what makes the throw longer?
can we just make a 80mm triplet like LL and change the powers of the lenses and focal lengths to get a longer throw with similar visual quality maybe better depending on the reflection I put on?
a 15in lcd with clear focus at 1024 is better then a 17 missing the corners.
 
on another side note would it be any easier to try and build a rear pj lens? something for a very short throw and a large image, would need to find a good rpj surface dont think there is one? just trying to find the best idea or way around this I just dont like the middle of my room filled with crap and a box blocking the view :(
 

Rox

Member
2004-07-25 10:06 pm
?
i thought your lenses would be near 80mm diameter :D. one of the best advantages of 135 triplet is it's clear diameter of 125mm. This is the largest lens we can have by now. I believe 80mm is good choice as well.

larger the positive focals are and shorter the negative focal is, longer throw lens you will have.
 

Rox

Member
2004-07-25 10:06 pm
?
yes I agree. But i prefer to have larger lens if posible :D

There should be light only going to the projected arc at the optical center of projection lens but i think you will agree that in real world it won´t be this way (fresnells aren´t very precise elemts so the projected arc will be more difusse (larger).

Conclusion; if our friend can use 100mm diameter lens, it is preferable agains 80mm. But a 250mm diameter lens, i agree it would be a waste of money.
 
I guess that doesnt make sense to me especially for a even lighted image? wouldnt the smaller lenses be easier to concentrate the light on? you just would need to focus the light into a smaller area isnt that easier? the LL triplet seems to work better then anything else if we could get something that well with a longer throw and larger fov I think most people would be happy. If a 135mm lens is that much better I will certainly ask and see what I can find out.
so say we want to do the 80mm diameter with a 17inch fov and atleast a 10-12 ft throw what types of lenses should I be looking for powers, and everything else? if you dont know how do we find out?
 

Rox

Member
2004-07-25 10:06 pm
?
do not mix things, the diameter of the lens has nothing to do with image size. A 10mm diameter would work for you but the image brigtenss would be very poor. The smaller diameter only will reduce de brigtenss.

lets say 110" (as you are teleling me ranges, i just need one value so i do the midleway like i did with your throw).

110/17=6,47 is the magnification you want.

6,47*D=11'=335cm So D=51,7cm


now: 1/EFL=1/51,7 + 1/335

EFL=447cm well, it lloks like the 135 triplet would do a good job for you if it wasn´t for it´s narrow FIELD ANGLE. (Do you agree that the image size projected by this 135 triplet is fine IN SIZE for you?
lets see the needed Field angle;

17" at 51,7cm this has near 46 degrees of full field angle.

now you need somewhere 450mm focal and 46 field angle projection lens.
 
I would say that it is good for size yes, it seems smaller but I havent moved it back far enough to really see. I would rather the 120 if that is doable so If that is possible with the lenses I can get that would be better I do work tmw so I will ask as far as the diameter and see if I can get a 100mm diameter. So for 120" image and the 17"lcd how do we figure out what lenses we need to make the triplet? is that something we need to find somewhere else? the size of the curvature? I am sorry I dont understand this stuff that well. how will we adjust for the fov? I am calling it a night Ill be back on tmw.
 

Rox

Member
2004-07-25 10:06 pm
?
first of all i would try some test with 80mm, and when you have the lens, then you can try to ask for larger diameter lens.

about the shapes of the lenses, it is done with precise compter programs, so aberrations are minimized with the best curvature radius and lens placement as well as lens materials.

I have no the knowledge enough on triplets to tell you the best shapes, i think try/error is the only way if you do not find any help.
 
so what do we know and where is a good guess for other specs? I can always bring in my triplet and show people and see if they can get something with similar curvature to that? but if that is what increases the field of view we want more then that right?

so we start with the 80mm but everything would change if we were going to go to the 100mm so how does testing with the 80mm help?
if you were going to order the lenses what would you start with? we have 3 lenses do we have any idea for starting points? I can take my 135 apart and bring that in for each element but we need to increase the field of view also and you think we should start with 80mm lenses so I dont know how close that would be? has anyone ever found specs on the lenses we have available now as far as powers or anything else?