Having just taken about 150 slides for a Siggraph course with good results, I would like to add one more long description of what works well for me. This is an update of a posting I made in January. (ed: of 1991. The original article appeared in June of that year.)
You will (obviously) need a tripod to hold your camera. A cable release is helpful in reducing camera vibrations, but it is not absolutely necessary.
Obviously, the camera should be an SLR (or maybe a Hasselblad!).
Peter Cahoon
has both a 35mm SLR camera and a tripod. Remember to ask politely!
A good daylight film produces best results on a color monitor because
it is sensitive to the same colors as the phosphors on the monitor.
For slides, Ektachrome 50HC works very well. For prints, Ektar 25 is
probably the best you can get. The slower the film speed the better
the results you can expect. Slower films have a finer grain as well as
allowing you to shoot at slower speeds which gives you more even light
distribution.
I've gotten satisfactory results with Fujichrome and Fujicolor ASA 100.
Fine grain is more important if you are producing slides.
Kodachrome and Kodacolor are reputedly less satisfactory.
You are more likely to get a good color match with slide film because
the photo processing lab does not attempt to do any color adjustments
on slide film. Nearly all prints have some color adjustments done on
them which can change your results.
Before you start shooting pictures, make sure the color CRT is totally clean. The darker the room the better. Be sure there are no reflections off of the CRT from any other light sources. It is also a good idea to make sure no other bright CRTs are nearby.
The Imager/dark or GraFiC labs should be ideal for this purpose, especially
since the IBM RS/6000 screens (i.e., brutus) are flatter and therefore less
prone to distortion than the SGI screen.
The "demo" program (which should be documented)
is well suited to portraying image files for the purposes
of photographing the screen.
The image files must be in our (actually, Toronto's) own RLE format, which is
not to be confused with the Utah RLE format.
[We should add a link here to a description of formats.]
Align the camera and screen so that the screen is centered both
vertically and horizontally relative to the lens of the camera.
Contrary to what other posters have said, the further back from the
screen you can get the camera, the better results you will have. If
you have a zoom lens, zoom in all the way and move your camera back to
get the right sized picture. I use the 70 mm setting on my camera.
Moving back reduces the distortion caused by the curvature of the CRT.
Also, if your camera has autofocus as mine does, get the focus right
once, then turn the autofocus off.
Because the electron beam sweeps over the face of the CRT somewhere between 50 and 76 times per second, you want the exposure time to be very slow. I prefer to catch at least 10 sweeps of the electron beam to guarantee even light distribution. I never set the speed faster than 1/4 second. Most of my best pictures with dark backgrounds were shot at 1.5 seconds.
You can't always trust the light metering system to get an accurate reading from a CRT, but my camera, a Canon EOS Rebel, comes quite close. If you want the very best pictures from a CRT screen it is recommended that you bracket the exposure by shooting half an F-stop to either side of what your camera recommends, in addition to using the setting the light meter selects.
Also, if your image does not fill up the viewfinder
and your camera averages over
the whole scene, the non-black parts of your slide might be overexposed.
A full F-stop down might be more appropriate than half an F-stop.
If you need to shoot a lot of images, you should use up one roll of
film just getting the settings right. Get it developed and look at the
pictures before shooting your important images. I took 10 shots of one
text slide varying both the CRT gamma setting and the exposure to get
one slide that I was happy with. It turned out in this case that
raising the gamma setting and reducing the exposure looked best when
the slide was projected. I was then able to shoot 36 slides without
worrying about bracketing each one, because I had the right setting.
If you must have prints and want the best color reproduction, you will probably have to take something to the lab that they can use to match colors. The image called "lenna" is an excellent one for getting good color matching, since any good photo lab can produce a correct flesh tone.
If you are shooting many different images, keep in mind that brighter images will need a different exposure setting than darker images. This should be obvious, but I ran into that problem once.
One other hint for your film processing: make sure the first photo on your roll of film is bright to both edges. The film cutting equipment usually aligns to the first shot and lines up the rest of the photos based on where the edges of the first one are. I had about five slides with the edges cut off a few weeks ago because all images on the roll had black backgrounds. I had to hurry and shoot another roll of film to get all of the pictures I needed.
There are several choices for fast local film processing.
For prints, there are two one-hour turnaround places on 10th east of Blanca.
One is directly across from the Safeway and the other is adjacent to it.
For slides, there's a London Drugs on Kingsway near Joyce
that offers 2-hour turnaround on
Fujichrome (and Ektachrome, but not Kodachrome) slides.
Last updated by
Bob Lewis
on 21 Oct 93.