DLP projector for stereograms

Justin W · Post by **Justin W** » Tue Feb 01, 2011 11:47 pm

Now that we're cookin' with gas, I'd like to move my questions one step downstream - to the diffuser screen.
I'm not sure whether to go down to the glass shop and buy a big ol' sheet of ground glass or frosted glass or what (and have to confess that I'm not even certain what the difference is).
Alternately - if neither ground glass nor frosted glass is the best choice, what would be ideal?

Thanks again everybody for all your help with this daunting endeavor!

MrPat · Post by **MrPat** » Wed Feb 02, 2011 6:35 pm

Hi folks,

I used to work at Displaytech. They make ferroelectric liquid crystal displays. While it is true that microdisplays have used color wheels, it is not necessary and it is irrelevant to a microdisplay's intended use in a holography setup. As for field sequential color, it is not necessary for a hologram. If, for example, you wanted to create a hologram from a video still, one way is to convert the image into a grayscale image first. Alternatively, split the red channel into 3 channels, matching impedance (very important), and feed the 3 signals into your RGB input.

About the DLP motion. There is no way that you will see any vibratory effect. You are talking about little Al mirrors that are about 10 microns by 10 microns. They tilt to turn on and off. The mass of the supporting substrate must be 100,000 X the mass of all of the mirrors. Liquid crystals would not show a vibratory effect either.

Good luck with this. I think it'll work.

MrPat

holomaker · Post by **holomaker** » Thu Feb 03, 2011 8:49 am

MrPat wrote:Hi folks,

. While it is true that microdisplays have used color wheels, it is not necessary and it is irrelevant to a microdisplay's intended use in a holography setup. As for field sequential color, it is not necessary for a hologram. MrPat

the problem is if you diable the above (and light source), chances are you will get some kind of error code and the projector wont operate properly.

jnhong · Post by **jnhong** » Thu Feb 03, 2011 11:07 am

holomaker wrote:
MrPat wrote:Hi folks,

. While it is true that microdisplays have used color wheels, it is not necessary and it is irrelevant to a microdisplay's intended use in a holography setup. As for field sequential color, it is not necessary for a hologram. MrPat
the problem is if you diable the above (and light source), chances are you will get some kind of error code and the projector wont operate properly.

This is true for projectors that use lamps and fans and color wheels, and also those with laser diode modules. It may not necessarily be true for RGB LED picoprojectors -- I've looked at the ribbon cable assemblies for the LEDs and I have not seen a clear feedback or monitoring mechanism. This is not definitive, but because of the low-cost design it doesn't seem to have an extensive feedback system. I'm continuing to work and see if this is the case (but don't hold your breath).

Justin W · Post by **Justin W** » Thu Feb 03, 2011 2:01 pm

Hello again folks.

Indeed the Pico was my projector of choice from the very start because of its size and simplicity. Without any moving parts I was not concerned that I would wind up trying to reverse-engineer whatever system I understood color wheel models to use. As it turns out - after reading that MIT paper - the closed loop feedback the wheel delivers is possibly simple anyways. Until grazing my eyes across the surface of that document, I hadn't known that the color wheel doubled as an optical encoder! Too cool. With that knowledge on board, I bet one could just calculate the specs of the square wave fed back into the system by that encoder (it's probably not even quadrature), and mimic it with something cobbled together with a 555 chip or something. I don't know sh*t about electronics so I'm super glad that I'm personally not looking down the barrel of that gun, but I bet if crunch-time came, even my dumb self could get something to work.
Big talk.
As it turns out, though, I don't have that bear to wrestle. My Pico may be here as soon as next week sometime, and I'll be reporting back veruh soon with whatever news I discover related to trying to burn a test image with the lil guy.

konsew · Post by **konsew** » Mon Feb 07, 2011 1:08 pm

Here are my experiences with modified DLP projector for stereograms. I bought Infocus X2 projector and I converted them for holographic work. I chose it because it was easy to bypass the lamp. There is also better X3 version with XGA resolution (1024x768). So far it works as it should, I got nice projected image on the screen (I didn't make any exposures yet). Total cost including projector, machining etc was about 150$. Now I need design and make holder wit moving slit.

Infocus X2
http://www.projectorcentral.com/InFocus-X2.htm

after modification

holomaker · Post by **holomaker** » Mon Feb 07, 2011 1:18 pm

can you supply us with the information needed to bypass the lamps ? were you also able to disable the color wheel as well? thanks

konsew · Post by **konsew** » Mon Feb 07, 2011 1:43 pm

Bypass the lamp
http://www.diyaudio.com/forums/diy-proj ... ass-2.html

The color wheel is connected all the time (inside the grey box). Without it projector generate ugly image (something like black and white without grey shades). It vibrates and sit on my table (it doesn't harm my fringes even slightly! but it depends how good is your table).

holomaker · Post by **holomaker** » Mon Feb 07, 2011 2:04 pm

This is excellent news! ill need to pull out my infocus #910? Was that the model #? Any way ill try to apply this info to see what happens... i appreciate your effort here as i stated above my biggest problem was the darn bulb in the box thing.

PS i like the "wheel in the box thing" i can wait to give it a try!

Ed Wesly · Post by **Ed Wesly** » Mon Feb 07, 2011 5:17 pm

Alternately - if neither ground glass nor frosted glass is the best choice, what would be ideal?

The ground glass diffuses by refraction, will preserve polarization, and its angle of view and resolution are tied in to how it's etched. You might have to try a variety of samples to find one that you like. Then there is flashed opal glass, it diffuses by scatter, so it screws up polarization, but it looks much smoother. And wastes more light. There might be some specialty back projections screens, see if you can get some samples, and project images on to them, like the previous, and see what looks right for you.

At CFC/Northern Banknote we had some sort of coated glass, and all you had to do was touch it and it left a mark. And it scrambled polarization. Don't recall where it came from.

Keep up the good work!