DLP projector for stereograms

Justin W · Post by **Justin W** » Sun Jan 23, 2011 5:38 pm

Hello all!

This is a neat new forum and it's good to see the gang's all here, along with a few new members. Great stuff.

My reason for posting today is an interest in turning over my table to some stereogram work. I'll be capturing source images in high definition via an automated system that I am currently wrapping up the design of. Slit translation will also be computer controlled, and it's all working out to be a very involved and certainly expensive project by the time it's completed. For these reasons I think it might be a really good idea to make sure I don't run into any nasty surprises down the road .

What I am hoping to be able to do is project my sequence of images onto ground glass with my 215M shooting a raw beam into a DLP projector. The projector I have in mind is the Optoma PK201 Pico projector. I have chosen this particular unit because it claims to be capable of HD imagery. I am hoping it will be as simple as opening the case, gently removing the R,G, and B LEDs, tucking them in a tiny light-tight box while still attached to the ribbon cable, then aiming a raw object beam into the open green hole and projecting a laser image a short distance onto my diffusing screen. Grayscale images will be transmitted from computer to projector one at a time via USB 2.0, toggling from one to the next between exposures by the grace of the code I need to write.

I'm concerned that I've seriously over-simplified this and am setting myself up for an expensive disaster. Might anyone have any experience with this or perhaps a better idea that you would be willing to share? I understand LCD screens are often used for this part of the process but don't trust myself to disassemble one without damaging it or know how to operate it at runtime.

Thank you for any help!

holorefugee · Post by **holorefugee** » Tue Jan 25, 2011 1:19 pm

You also will need a moving slit. The best work I have seen is using the DLP chips and not the LCD. I am not sure which that projector uses but the projectors that they are taking the blue lasers from uses DLP and the laser forums have them really cheep with all the lasers removed.

Justin W · Post by **Justin W** » Tue Jan 25, 2011 3:59 pm

Hi Holorefugee

Yes, a second robotic device will translate a slit in either 32 or 64 steps across my filmplate (between exposures and with a few seconds to let motor vibrations subside), while Flowstone program changes images to projector between shots.

Justin W · Post by **Justin W** » Tue Jan 25, 2011 4:02 pm

Oh and BTW yes the Optoma PK series projector use DLP technology. This sounds better to me than the liquid crystal on silicon option other projectors sometimes use. The LCoS jobbies often go "color-sequential", which sounds like a lot of stuff in constant flux (movement probably causing instability).

holorefugee · Post by **holorefugee** » Wed Jan 26, 2011 10:19 am

Justin W wrote:Hi Holorefugee

Yes, a second robotic device will translate a slit in either 32 or 64 steps across my filmplate (between exposures and with a few seconds to let motor vibrations subside), while Flowstone program changes images to projector between shots.

A stepper motor on a fine screw will allow a variety os slit widths to be used. Slit widths can be as small as your pupil size but that is about the limit. Figure 5mm might be the smallest width you would ever use. If you are really abitious make sure you can set up vertical and horizontal slits. It will allow for motion of the stereogram objects in a handheld hologram. 20x20 pixles on a 2.5" plate could makke a pretty fun hologram but 400 exposures all the same brightness is not an easy task.

Justin W · Post by **Justin W** » Wed Jan 26, 2011 6:56 pm

Yo again

Yeahman a stepper motor (bipolar for torque and resolution) will definitely be actuating slit movement. A design I had drawn some time back incorporated a lead screw (actually a pair - one on either side of the slit), but right now I'm on the cusp of fully realizing a different idea.

I think for the beginning stages of my multiplex work I'll be topping out at 64 exposures per. I think that makes an 1/8" slit on 8x10.

PinkysBrain · Post by **PinkysBrain** » Thu Jan 27, 2011 11:05 am

Justin W wrote:Oh and BTW yes the Optoma PK series projector use DLP technology. This sounds better to me than the liquid crystal on silicon option other projectors sometimes use. The LCoS jobbies often go "color-sequential", which sounds like a lot of stuff in constant flux (movement probably causing instability).

DLP is colour sequential too, in fact it's PWM ... that said, the phase delay is probably more stable in DLP.

Justin W · Post by **Justin W** » Thu Jan 27, 2011 11:54 am

OK now we're getting to the meat and potatoes of my concerns. Excellent!

Please correct me if I'm wrong, but I was under the impression that color-sequential projectors use a color wheel in their process. In my sporadic research to date I've led myself to believe that the color-sequential style units spin this color wheel in front of a white bulb and time pulses of light through appropriate colors in the wheel to approximate full color via momentary blasts of component colors mixing too quickly for the human eye to register.

Optoma's PK series has no color wheel. In fact, I've seen it noted that they have no moving parts whatsoever. This particular line of projectors utilizes an RGB LED system, which I was hoping meant that it mixed the component colors simultaneously by the grace of some nifty micromirror process.

Whatever the means of color mixing is probably academic until I reach the point in my multiplex future where I am using an RGB laser system to make full color images. The grayscale images and single green laser I'll be using in the interim might be fine with almost any projector arrangement, but it would suck out loud to discover down the road that my projector is unstable for holography in full-color mode.

Thank you everyone who's been posting on my topic! This is new territory for me and I can really use all the help I can get.

Justin W · Post by **Justin W** » Fri Jan 28, 2011 11:39 am

Well, golly.
OK so that's some big hopes dashed.
I adjusted my research settings to "bad news" and found some.
Turns out the Optoma PK series Pico projectors are color-sequential. They're color-sequential all day long.
Which I assume means that those lil' red, green and blue LEDs are ever-so-quickly cycling redgreenblueredgreenblueredgreenblue while the micro-mirror array busily reorients itself oodles of times a second to display individual color channels in rapid succession...
Such manic behavior would not be tolerated from any of my other mirrors, so I'm not about to let it slide here.
Hopefully the DMD won't take such a frenetic approach to displaying grayscale images, and when the time comes to introduce a red and blue laser into my multiplexing setup, it will be a matter of Photoshopping all the images into separate color channels and exposing them one at a time - in essence doing what the projector does except in super slow motion...?

holomaker · Post by **holomaker** » Fri Jan 28, 2011 7:39 pm

I’m excited to see this Justin, it will take much effort to make it work! Im not to sure about using these little Pico type projectors, they are so small it would be hard to reverse engineer it ! I’m thinking more about these Casio projectors now as it would be a fairly easy thing to get the laser light inside it, the laser module is removed from underneath. I'm just on the fence if i want to tear into my last projector!