🚀 go-pugleaf

Some additions/corrections to the posted info:

>3)	Most electronic metering systems will not properly meter a
>	flickering source (like a CRT).  Older "electromechanical" meters
>	will.  (Luna-Pro, cheap handheld meters, most needle-type meters
>	in general.)  You can't use your camera's meter to
>	read the exposure, unless it's of the electromechanical type.

The Minolta Spotmeter M (and probably the newer Spotmeter F) do a fine
job of measuring flickering light sources such as a CRT.  The Pentax
Digital Spotmeter definitely does not work.


>4)	When you meter the screen, turn off the lights and place the meter
>	directly on the display, pointing it at a NEUTRAL, relatively dim
>	area.  If you're photographing a display of lines, you'll have to
>	meter something else to get your exposure.  Meters are calibrated for
>	a reference subject of 18% reflectance.  Ideally, you'd want to
>	meter something that was 18% as luminous as your display's "white,"
>	but there's usually no practical way to do this.  So you'll have
>	to guess, and...

Well, you can display a grey patch of 18% of full brightness and meter
that, but unless you've done very careful "gamma correction" of your
monitor, this won't be accurate.  Instead, display a white patch in the
centre of the screen (since intensity falls off at the edges) and
measure it with the spotmeter, or a standard meter up close.  Then
give 2.5 stops more exposure than the meter indicates.

Since the log to the base 2 of 0.18 is -2.47, this is equivalent to
measuring an 18% grey patch but doesn't depend on gamma correction.
Another way of thinking about it is that 2.5 stops is the appropriate
exposure increase to place the measured area of the picture (full white)
at the upper end of the linear response curve of a transparency film.
Negative films can generally take even more exposure.

So, for example, if the light meter read f/11 for the white patch,
you would set the lens diaphragm halfway between f/4 and f/5.6.


>5)	BRACKET YOUR EXPOSURES.  A minimum of three exposures per display
>	is advisable.

The first time I tried the above technique of using a white patch for
reference, I bracketed the exposure widely with tests spaced every
1/2 or 1/3 stop.  The exposure calculated by the meter turned out to
be the best.  Since then, I never bracket, I just trust the meter,
and all exposures have been fine.


>6)	If your slides have a pronounced color bias you'll need to try
>	filtration.  Use CC ("color correction") filters, and experiment until
>	you succeed.  This is a complicated procedure for the amateur
>	photographer, but basically you'll need gelatin filters and
>	a gelatin filter holder, both of which can be ordered from a good
>	photo supply store.

If you don't have a gelatine filter holder, you can always use adhesive
tape on the corners of the filter...


>7)	A mild telephoto lens (about "portrait length"-- 85-110 mm) is best
>	unless you're photographing a particularly large screen.

I second this.  I use 135mm.

>8)	A GOOD TRIPOD is essential.  A remote shutter release is almost
>	as essential, unless you have either a self-timer or have a very
>	light touch on your shutter button.

Yes, and also make sure that the camera's lens is as close as possible
to the centerline of the CRT face, both vertically and horizontally,
to avoid distortion.  Focus very carefully.

One final point: I always use a shutter speed of 1 second.  Long exposure
minimizes any effects of the shutter not being synchronized with the CRT
refresh, and 1 second is the longest exposure my camera will time for me.