Syncing with a projector for back projection.

[I Bloom]

Getting ready to shoot a commercial that uses a rear projection background. The projector is a Dell MP5100 DLP projector. We did a test and as expected we get horizontal strobing on from the projector. I know the a 144 degree shutter can get rid of this problem from a TV does anyone know how to do this on a red? Specifically do you understand the finer points of the shutter menu?

IBloom

 

[I Bloom]

Update,

Testing on an LCD projector, as expected no flicker problems, but the LCD quality can't stand up to the 4K image.

 

[Dan Hudgins]

Filter wheel issue?

Filter wheel issue?

I am not sure about your DLP but some DLP use a filter wheel, you can tell if you wave you hand with the fingers spread side to side, if you see color shadows then the color is seiral rather than parallel, in that case the 144 degree trick may not help if the projector is showing the colors in shorter durations.

If you could run 10 DLP projectors at once on the screen it might reduce the flicker since the filter wheels would be out of sync? And you get more light? Not a good solution, but something...

You can put a photo cell in front of the DLP projector and hook it to your computer's sound board mic input and record a wave file to see what frequency the DLP projector is running at (count the samples between the peaks, record at 48000). Or use a 'Scope if you have one...

I have thought of adding a photo-cell input to the sync circuit for some of the movie cameras I use in the field to sync to florescent lights and TV monitors since the Crystal motor will drift over 400' and you get a slow exposure change, that would not happen if you lock the sync to the light pulses...

Here is a link on the DLP filter wheel,

http://www.projectorreviews.com/advice/dlpvslcd/index.php

You may be able to build a high res LCD projector using a 1920x1200 LCD, by taking the back off, using a large lens and image lens from an opaque projector and pushing a 5k HMI with heat filters through it, see this link,

http://www.diyprojectorcompany.com/

http://yhst-18925554572786.stores.yahoo.net/

http://www.inventgeek.com/Projects/HomeTheater/Overview.aspx

http://louisville.edu/~wchall01/diyprojector/overheads.htm

Using LCD in this way may be a help in getting more light to build a film recorder as well...

Another idea is to use a 70mm film background projector, and use the photo cell on the RED (tm) monitor, then drive the projector's sync motor from the RED (tm) camera vertical sync that would give positive phase lock...

 

[casinowilhelm]

Update,

Testing on an LCD projector, as expected no flicker problems, but the LCD quality can't stand up to the 4K image.

Hi there - we are organising a shoot using a RED camera which heavily involves projections (onto people etc). We're trying to figure out whether we'll have these kind of strobing issues. Any chance you could describe your setup (which LCD projector you used, camera frame rates, shutter speeds etc) so that you didn't get strobing? Thanks, Mike

 

[David Rasberry]

LCD projectors are a better choice for this. Single chip DLP's are likely to exhibit artifacts that can't be eliminated by shutter timing.
On both types the flicker is determined by the source signal, just as it is for a monitor. Changing vertical refresh rate of your display source if its a computer, as well as adjusting shutter angle, can help eliminate the problem.

 

[Dominic Jones]

Yes, LCD is ideal from an exposure point of view, but I'm guessing that Ian is having problems with the "chicken wire" effect of the LCD panel showing up...

If that's the case, the only thing I can think of regarding the LCD projection is to try (assuming you haven't already) a projector with "smooth screen" technology or similar (the Panasonic PT-AE2000/3000 springs to mind if it's 1080p material being projected), as these do a very good job of smoothing out the space between pixels without loosing undue levels of detail in the image.

Otherwise, either lots of testing to determine a DLP setup that works for you, or get it lasered to film and project 35mm...

HTH,
Dom.

 

[David Rasberry]

The easiest solution for pixel borders is to just slightly defocus the projector. LCOS projectors, JVC, Canon Realis, have much less visible pixel borders and would work as well.