At 1:31 PM -0500 5/23/01, Kiker, James wrote:
Hi list,
I have an assignment at work tomorrow to photograph a man at work in
front of two computer monitors (under fluorescent lighting).
[snip]
Unless the monitor has medium- or long-persistence phosphor, you've got
trouble. The electron beam rewrites the screen every 1/60 or 1/75 of
a second (or some similar number depending on what refresh rate the video
card is set for). The leaf shutter buys you a very little improvement
because its movement is essentially symmetrical with respect to the
screen, but basically the parts of the screen that have been written more
recently show up brighter than the parts written less recently. Anything
faster than the refresh rate of the screen is right out.
If your shutter speed *exactly* matched the refresh rate of the monitor
(i.e. to a small fraction of a percent) you would be able to take an
exposure during which all the lines were written exactly once. Otherwise,
if you have to do it all in a single shot, your best bet is to go long
so that the difference between the parts of the screen with extra exposure
and the parts without will be minimized. (For a comfortable subject you
can probably go 1/4 or 1/2 second or whatever...) You're also going to want
some kind of polarization if possible to minimize the reflections from the
screen.
But frankly, the best way to do this (and well within the budget of anyone
making a banner like that) is to take the picture of the guy, lit however
you can to make it look best, then gently slide him and his chair out of
there, turn out the lights and make some long (1s-plus) pictures of the
screen that some photoshop monkey pastes in.
paul been there, wasted a lot of time not doing that.
ps If you can get them to substitute LCD flatscreens for the monitors, that
would at least get rid of your timing problems
--
Paul Wallich pw@xxxxxxxxx
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