While I had my lens apart to clean the lenses and paint the spacers flat black I remembered that mikyd1954 wanted to know the spacing and focal lengths of this type of lens. Here you go.

2

3

4

excellent, thanks, I wish it was easier to find these , a s a side note have you seen the pro lens mod elken has made? wonder if you could boost this fl ..... what size lcd are you using going to use with this?

I have seen the pro lens mod and it may be possible to mod this 22" also. The cool thing would be if we were able to find lenses to cheaply (surplus shead) duplucate this lens. I'm planning on using this lens with a 17" lcd. I have all the parts ordered from Lumenlab so I'm just waiting for it to be shipped.

Does the 22" lens need to be modded ? Others that use the 22" seem to have focus and brightnes over the whole image ...

I too am going to use a 22" with 17" LCD. I got the lenses, I am about the get the 150 poweball .. I am still looking for an LCD

I calculated the bi-concave lens focal length to be between -165 to -175 mm. I couldn't see the thickness of the bi-concave lens (a little too blurry) so I guesstimated at 20mm.

Anybody else?

Tgreenwood

Thru the blur I read the thickness as 21mm.

Sorry guys I should have written over that in ink. It is 21mm in thickness and 9mm in depth of the curve.
I have corrected the pictures they are much clearer now.

Thanks for fixing that. I recalculated and for the triplet to have an effective focal length of 22 inches the bi-concave lens focal length is -158mm if the other two lenses are plano-convex.
I gave the focal length of 298mm to the principal plane of the front lens, and the focal length of 335mm to the principal plane of the rear lens in my calculation, and 60mm between principal planes of the three lenses.

If the other two lenses are slightly bi-convex then they are probably aspheric lenses and the best approximation I can get for the focal length of the middle bi-concave lens is -165mm.

Anybody gonna try making their own 22 inch EF triplet lens?

Tgreenwood

If I could find a source for reasonably priced, large diameter lenses I'd love to try making my own triplet. I've tried surplus shed a couple times, but their stock rotates often so it's hit or miss. I also think that the center lens is a different type of glass (crown or flint) than the outer lenses in order to correct for chromatic aberration. I'm curious if making the lens distances adjustable would let you adjust the size and focus of the final image.

The outer lenses will be Crown Glass while the inner lens will be Flint Glass. That is the typical Cooke Triplet design, the different glass types cancel out Chromatic Aberation.

I few years ago, when i first got into the diy projector scene i used lenses from eye glasses. They usually are rated in diopter, but that shouldn't be a problem. Just go down to a local eye glass shop and talk to the people about getting raw lenses in the focal length(diopter) you need. Try to locate a non chain store type of place since they are more willing to do the one off orders.

I started a thread a long time ago on trying to make a giant doublet. I was think of a doublet over a triplet mainly because it would be cheeper. For a 17" LCD a 8" triplet would be nice but with some of the high rez smaller panels llike the 10.6 the idea of adding a single large lens to reduce the fl of the pro lens to 300 mm or so starts to look good.

A 6" lens added to the pro lens with a FL of 300mm would have an F vaule of 2

This would allow for a reflector system to be around 5" in size.

This one is 8" but might work.

Click to view attachment

The old thread.

http://www.lumenlab.com/forums/index.php?s...st&p=131110

And a quick look at the F vaule of vthe triplets.

http://www.lumenlab.com/forums/index.php?s...st&p=122256