photographing the screen

[Steve Lehar]

Photographing the IRIS screen and making  slides is the most effective
way of presenting your results  at  conferences and  meetings, etc.  I
have done this several times, and the resolution of the slide captures
everything on the screen with  good fidelity,  especially if you  zoom
your imagex up 2x.

I  usually use a regular  35mm camera on a tripod  in a darkened room.
Be very careful about reflections on the screen- it is amazing how you
can look at the  screen and see  no reflections, but when you  look at
the pictures you see a prominent reflection  from a power or "on-line"
light  of a  printer or computer,  or from a  tiny crack in the window
shade.   Your brain filters these  things  out  because they  are at a
different focus- until captured on the photograph.

Be very careful  to level the camera- in  the  viewfinder measure  the
angle between  the  bottom of  the  screen and   the   bottom of   the
viewfinder- get them exactly parallel.  This is another thing that you
might  not notice otherwise, but looks  very odd when you project your
slides to  the audience with a 2  degree list to starboard.  Likewise,
center the screen exactly in the frame.

Move the pointer to the bottom-right of the screen where it disappears
except for one last pixel.  Again, if you  are not thinking,  you will
not notice the pointer because you are so used to seeing it.  When you
see the photographs however it will appear prominantly distracting.

Another thing   that strikes  you  when   you see  the slides  is  the
curvature of the lines due to the curved screen.   You normally pay no
attention to this because your eye compensates for it- like looking at
a line of lattitude on a  globe (looks straight)  compared to seeing a
projection  of that globe  onto a flat  map  (looks curved). Make sure
that you are looking straight-on at  the screen,  so that the curve-up
at the  top of  the screen is  symmetrical with  the curve-down at the
bottom.  This is done by aligning the camera exactly  on the normal to
the center  of the screen. The  curvature can be  minimized by setting
the camera far from the screen and using a zoom lens.

Use a film speed that will  "average over" many screen refresh cycles.
If you set your  exposure  to  1/30 of a  second for instance, you are
unlikely to catch exactly one screen  refresh,  probably 0.9 or 1.2 or
something,  which will create funny  looking results where  there is a
gap or  an overlapping region.   If you set  for  1  second, then some
parts of the screen will have been refreshed 30  times, and some parts
29, or 31 times.  This ratio is sufficient to make  the difference not
noticable.  I.e. use a long  exposure time- this means  of course that
you must either use a remote cable  trigger, or  a delayed trigger, to
avoid shaking the camera with your finger.

When using a built-in light  meter,  zoom the lens  to remove all  the
background blackness, set the lens till the  light meter is satisfied,
then un-zoom again for taking the pictures.  In other words, don't let
the border blackness (off  the screen) influence  the  reading  of the
light meter.  Straddle the  settings that the  light meter recommends-
i.e. take three exposures for each frame, at three  adjacent settings,
to make  sure that one  of  them is ok.   The perfect setting may well
depend on the type of image you have- are you interested in the detail
in those dark corners, or do you want to examine the brighter regions.
--
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(O)((O))(((               slehar at park.bu.edu               )))((O))(O)
(O)((O))(((    Steve Lehar Boston University Boston MA     )))((O))(O)
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