Build Your Own SLA/SLS

In order to minimise throw to keep my sla as small as posible, and reduce the number of elements in the lens, I made a holder from a salvaged two element unit, it has adjustment for focus.

Hi John,
Can you provide some details of how did you manage to reduce the number of elements in the lens?
Kind regards,
Vlad

Dear John,
I disassemble a projection lens totally, tried various combinations, none of them minimize throw.
Please see the attached image, it is a schematic section view of my projection lens.
Hope you have some advice,
Kind regards,
Vlad

sorry for the late reply, been installing solydx linux on my systems, my head has been elsewhere,

I have a few boxes of lenses I have collected over time, and kept trying them all untill I got the result I was
looking for, not very helpfull for you I am afraid, I have seen lens calculator online which may indicate what you need.

sorry not to be of more help.
P.S. from memory one lens was concave and the other convex, about 30mm diameter and approx 40mm apart.

In order to minimize the throw distance, you simply need to move the projection lens a few mm further outward from the frame. I FDM printed a small 3mm spacer for mine.

Hey John and Steve,
First of thank you for your reply, any advice is better then none. I found out that placing a flashlight in front of lenses and tried various combinations may teach about the way projection lens are working. Even simple flashlight from smartphone will do the trick. It's my first time addressing Steve, so I would like to thank him personally for the great job on his great contribution to our community, that partially at least owes its existence to him.
As to Steve's advice, moving the projection lens a few mm further outward from the frame created a blurring corners at offset projection lens. Lenses that had used in nontelecentric architectures projectors, like mp2800 projector.
Best regards guys,
You Are Great Aspiration!
Vlad

Instead of modifying the lens assembly(moving forward) I saw a suggestion of using close-up filter, not sure why they are called filters. I am working on my own build ATM and I'd prefer to keep the projector stock so that I can still use it as an actual projector, is this a viable option?

Also known as close-up lens:
http://www.amazon.com/Vivitar-55MM-Clos ... o+lens+kit

Although I haven't tried the close up filter/lens route, from what I've read so far they create problems around the edges making them blury.
For those interested Texas Instruments has a pdf on the subject of DLP optics that has all the formula for figuring to focal distances and correcting those.