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Shooting backlight LCD projector screens (smartboard)

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Herb Saperstone
Shooting backlight LCD projector screens (smartboard)
on Dec 19, 2008 at 4:41:44 am

I have begun producing (with a multicam switcher) some training sessions using a projector-lit (Front-lit) smartboard which requires projected images from a computer. I am using a common DLP data projector. I am shooting the session in a TV studio environment which is lit for the presenter. The presenter is usually off to the side of the smartboard where I can auto iris my cameras. Naturally, when he is backlit, I must use manual iris when he is touching the smartboard screen (becasue we want to see the presenter interacting with the board). I was wondering if there is an easy way to dim the output of the projector to allow for more even exposure? An ND filter or other for the projector? I know for big bucks I could buy a rear projection smartboard but in a school district, money is tight. The cast shadows are not as bad as the exposure issues. Any suggestions?

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Bill Davis
Re: Shooting backlight LCD projector screens (smartboard)
on Dec 19, 2008 at 5:33:04 am

If the issue is that the white board projector is simply too bright, get some ND gel and rig it over the LENS of the projector. If you buy a sheet of full stop. And a sheet of half stop. You can double, mix and match until you get the projector beam down to the right level to match your talent lighting.

Often with projectors - you not only have an issue of brightness, but one of color temperature as well. Projector bulbs are often have a skewed CRI that's nearer to daylight (5600K+)

Depending on the room lights (tungsten? fluorescent?) you might have issues with color balance.

You can combine the ND with CTO to warm the projector closer to tungsten lighting - or combine the ND with Plusgreen to better balance with spikey fluorescent room lights.

But the ND by itself should get the intensity into the correct range for a good exposure.

Let us know how it works for you. Good luck.

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Mark Suszko
Re: Shooting backlight LCD projector screens (smartboard)
on Dec 19, 2008 at 3:22:22 pm

Can you post a diagram or still photo? It would help. Do you have the projector beam flagged off so it is only hitting the screen and not spilling off anywhere else?

Do you control the studio lighting, or are you stuck with the grid as it is now? What I'm getting at is I have a suspiction your contrast ratio is just too great. This could be tweaked on the lighting side, the projector side, and you could also make set changes. Or a combination. I'd have to see it and know how you use it to have a better idea.

But one thought occurs to me: can you put grey photog paper on the smart whiteboard and still have it work? Are the pens actually drawing on the surface during the presentations, and does the presenter need to erase and re-draw a lot, or do they just keep adding to the board all thru the show? You notice TV talk show hosts tend to use non-white note cards on camera, and I think a lot of that is to reduce that hot spot in the picture.

A grey board would lower the contrast but probably still reflect enough of the projector to read okay, especially if you pick colors in the projector content that contrast well. If the presenters really draw on the surface and also erase, then this plan will not be practical. But maybe painting would.

Just an idea, it may or may not work. But you could test it with some scotch tape and about eight dollars worth of grey poster paper.

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