PHOTOGRAPHING VIDEO
                       By Ted O'Hara

Are you sick of hovering over your printer, waiting for your print-outs to (finally) be finished?  Are you dissatisfied with the results that you get from your printer, in terms of banding and color saturation?  Would you like to use your graphics in presentations?
   Photographing your monitor (or other cathode ray tubes, like televisions) is not difficult. The techniques are simple, and you may very well already have the necessary equipment.  This article will discuss those techniques, and film and equipment choices necessary to produce good photographs from your computer monitor or television.

Persistence of Vision______________________________________

  All cathode ray tubes work by spewing beams of electrons at a phosphor coated screen.  When the electron strikes a phosphor, the phosphor lights up.  Color monitors use three electron guns and three colors of phosphors to produce red, green and blue light, which, when mixed, combine to form other colors.
  Television and monitors form their images by scanning them (this is called raster scanning).  The image is scanned top to bottom every 1/30th of a second.  Because human vision cannot react to rapid changes, the image of the phosphor appears to persist, even though it is flickering off and on every 1/30th of a second (this effect, called the persistence of vision also allows the illusion of motion from a series of rapidly changing still pictures.)
  Unfortunately, this effect doesn't work when taking pictures of the screen.  If you just snap a picture of your monitor at the speeds your camera normally uses, only part of the picture will be illuminated; the rest of the phosphors will have gone dark. The trick is to use an exposure time long enough to allow the picture tube to make (at least) one complete scan of the image.

Equipment__________________________________________________

  The first requirement when taking photographs of a monitor or other CRT is a camera with shutter speeds extending down to at least 1/30 of a second (and 1/15 is better, for reasons I'll explain later).  This generally means a single lens reflex camera, also known as an SLR. (Single lens reflex refers to the fact that there is a single lens both taking the picture and serving the viewfinder, with a mirror reflecting the image up to the finder when the shutter is closed).  These shutter speeds have to be either directly or indirectly user selectable.
  These two requirements generally disqualify the popular point-and-shoot cameras, but that doesn't mean you have to spend a lot of money on a camera.  If you look through the classifieds, you can probably find a good, used, bare bones SLR for around $100-200 (maybe even less).  It won't have all the up-to-date bells and whistles on it, but you don't _need_ them either.

  The second requirement is a lens.  SLR's have interchangeable lenses, which means that they are sometimes sold with no lens at all.  Usually, though, they come with a 50 mm lens, which is sometimes called a normal lens, because it has a angle of view roughly equal to that of the human eye.  It is certainly usable, but if possible, it's better to use a slightly longer lens, like a 135 mm.  This is a medium telephoto, which makes it possible to move the camera further away from the screen.  The closer to the screen you are, the more noticeable its curvature is.  Using a longer lens makes the screen look flatter and squarer.  (A medium telephoto lens is also great for portraits).

  The final requirement is a sturdy support for the camera. It's impossible to handhold a camera steadily enough at the shutter speeds necessary to capture a video screen.  Usually support means a tripod, but you can also use a stack of books resting on a table, or some other juryrigged support, as long as the camera is kept steady.
  You may also want to use a cable release to avoid jiggling the camera while pressing the shutter release. A cable release (usually) screws into the shutter release button, and allows you to make an exposure without imparting any vibration to the camera.

Film Choices_______________________________________________

  There are basically two factors when deciding on a film: film speed and film type.
  Film speed is a measure of the film's sensitivity to light.  Manufacturers determine the speed of the film by varying the size of the silver halide grains that make up the light sensitive emulsion of the film.  The bigger the grains, the more sensitive they are to light, and the faster the film is. The finer the grains are, the slower the film is.  Film speed is expressed by an ISO number; the higher the number, the more sensitive to light and the bigger the grain will be.  Most films have their ISO in their names, for example, Kodak Gold 200, Fujichrome 400, etc, but there are exceptions
  Generally, you want to stick with the 100-400 ISO range when shooting your monitor.  You don't need the extra fineness slower speeds provide, and they will require you to use fairly slow shutter speeds.  Conversely, you should avoid the higher speed films because their grain might be enough to be objectionable, you don't need the extra speed, and they cost more.

  The principal types of film are black and white print film, color print film, and color slide film.  Which type to use depends on what you're using the picture for.

  Black and White is most useful to people who need or want black and white pictures, or who are developing their film themselves.  Some newspapers will only accept black and white pictures, and some people prefer the aesthetics of a black and white print.  A major practical consideration for people who have access to a darkroom is that black and white is much simpler to both process and print than color---the temperatures are closer to room temperature, the tolerances are not as tight, and you can use a safelight when printing black-and white.
  In this country, Kodak basically has the black and white film market sewn up.  They sell two classes of black and white film: their amateur films, Plus-X and Tri-X, and their professional films, T-Max 100 and 400.  The professional films are finer grained and sharper, but are more sensitive to processing variations.  If you're sloppy in the darkroom, don't use the T-Max films.

  Color print film is the most popular kind of film in the country.  Color print film provides the easiest way to get color prints, it's quite easy to find someone to develop the film rapidly, and the current crop of films are generally excellent.  When you shoot color print film, the film develops into a color negative, from which you can easily make prints.
  When shooting color print film, it is especially important that you find a lab that you like and trust, because your final image depends not only on how well you shot the picture, but on how well the lab prints it.  If you like the way the lab does your pictures, stick with them.  If you don't, find another.  There's no sense battling a lab constantly, trying to get pictures made over.  Find another one that prints the way you want them to.  
  As for brands, Kodacolor and Fujicolor films are easiest to find, provide excellent quality, and the lab's printer is most likely to have a good color balance for them.  The printing channels for the other films are not likely to be checked as often.  Konica and Agfa make good print films too.

  Slide films are best when you need slides, (for a presentation, for example) or would prefer not to have the lab influencing the final result so much.  When you develop slide film (also called transparency film), the film that was in your camera is developed into the actual positive image, with no intermediary step.  Although it is possible to make prints from slides (using internegatives or a process called Cibachrome), it is expensive and the results are not always satisfactory.  
  There area couple distinctions to bear in mind when choosing a slide film.  The first is the kind of light the film is balanced for.  Although the mind's eye tends to correct for it automatically, incandescent light is much yellower than daylight.  When dealing with color negative film, the color balance can be corrected to some degree in printing, but daylight balanced transparency film will look quite jaundiced if you expose it using incandescent light, so the manufacturers make two kinds of slide film, daylight and tungsten.  Tungsten film is used for shooting under incandescent light, daylight film is balanced for daylight and electronic light. (Neither film is balanced for fluorescent light).  When shooting a video screen, use daylight film.
  The second consideration is the type of process used to develop the film.  The Kodachromes use Process K-14, the Ektachromes and Fujichromes use Process E-6.  The Kodachromes offer better sharpness and color, but since the lines of the video screen are the limiting factor in your image, you don't need the extra image quality, and Kodachrome usually takes several days to process. You can usually find someone to develop E-6 in a couple hours (in major cities) if look around, and it is possible to develop it yourself, if you really want to.
  There is also a third alternative: Polachrome.  Polaroid makes a series of almost instant 35mm slide films.  You expose the film normally, then develop it in a black box called the AutoProcessor. A minute or two later you have finished slides, ready to be mounted.  AutoProcessor films don't look too great on a light table, but in a projector, or in front of a strong light source, they are quite good. Polaroid makes several AutoProcess films:  Polachrome, Polachrome HC, a higher contrast version, Polapan (the easiest way to make black and white slides) and Polagraph (high contrast black and white).  Polaroid bills Polachrome HC as being good for photographic computer screens, experiments show that the normal, lower contrast version is slightly better when photographing graphics with a lot of mid tones. You might want to consider using Polachrome if you often need to make slides very fast; it is quick, convenient, and easy to use.  On the down side, the film is expensive, and requires an AutoProcessor to be developed; the image quality is good, but not as good as a conventional type film, and the film speed is relatively slow, only ISO 40.
  Among the conventional E-6 slide films, your main choice comes down to Kodak and Fuji.  Fuji is a little harder to find; Ektachrome is ubiquitous.  If you like supersaturated colors give Fujichrome a whirl--you won't be disappointed. If you like your colors a little more natural, stick with Ektachrome.

Making the picture_________________________________________

  With your camera filled with the film of your choice (be careful loading please...it's easy to misload 35mm film), put the camera on its support and compose your picture.  It's best if you can fill the frame with the video screen.  Your camera will meter the scene more accurately, and the printer will print it more accurately.  Turn on the computer and monitor, and darken the room, so you don't get reflections from the front of the screen.  DO NOT USE FLASH. Set the shutter speed to 1/15th of a second or slower. Since an image is scanned every 1/30th of second, you want to allow an exposure time long enough for the monitor to make a complete scan, even if (as is likely) you're not quite in sync with the monitor's scanning.  (If you use 1/30th of a second, chances are you'll be out of sync with the video, and you'll get a darker bar across the screen).
  If you're using a camera with aperture preferred automation, choose an aperture setting (f/stop) such that the camera chooses an exposure time of 1/15th or slower.
  If you're using a camera with shutter preferred automation, choose a shutter speed, 1/15th or slower, such that the camera stops the lens down one or two stops form being wide open.
  If you're using a programmed exposure camera, make sure the camera is selecting a shutter speed of 1/15th or slower. If it is not, switch to another exposure mode.
  If you're using a manual exposure camera, have the computer display an neutral screen (not too light, not too dark) set the shutter speed to 1/15th or slower, and close the aperture down at least 1-2 stops.  Choose a combination that cause the meter to indicate proper exposure, while still maintaining a shutter speed of 1/15th or slower. If you have to use a slower shutter speed to get the aperture you want, that's OK.
  If you're using an Apple IIGS, one idea is to use the text based control panel (invoked by pressing apple-control-esc) to temporarily set the text screen to a dark gray background and border, with light gray text while metering the exposure.  While the computer the computer is still displaying the control panel, set your exposure, then press esc. and exit the control panel.

  Once you have have the camera controls set up the way you want them, set up the computer display the way you want it. If you want to show a pull down menu, for example,  pull it down.  Once everything is the way you want it, make sure the camera is still, then gently release the shutter.
  If you're using print film, you can probably get away with one exposure per screen that you want to photograph, because the printing should compensate for minor exposure variations (you may want to deliberately overexpose by 1/2 a stop to give yourself some leeway).  Slide film is not so forgiving.  You should bracket your exposures.   Bracketing means making additional exposures of your pictures with more and less exposure than the meter calls for. The first time you use a given film you should probably bracket a stop and a half in each direction, in 1/2 stop intervals. Once you get the film back, you can look at the pictures and decide whether or not to bias future exposures.
  Bracketing is easiest to do in manual exposure mode--just move the aperture ring on the lens a click or two each time.  Most automatic cameras have an exposure compensation dial--turn that a notch or two each time, following the directions in your camera's manual.  Be careful when using exposure compensation that the camera does not select too fast a shutter speed.

Processing_________________________________________________

  Properly exposed monitor pictures do not require special processing.  Slide films certainly do not.  With print films, some labs have a tendency to make the prints too light, although this is more of a problem with graphics that are displayed against a black background, than it is with displays of the Apple Desktop interface.  The problem is that pictures with large black areas tend to be read by the printer as underexposed and the computer shortens the exposure time to compensate.  In these cases the printer operator has to tell the machine to add exposure.  If the lab is on its toes it should do this without intervention on your part.
  If you get prints back that look too light or dark, look at the negative.  If the light parts of the picture look light on the negative, then you underexposed the picture and there is nothing that can be done with that negative--it'll have to be reshot with more exposure next time.  On the other hand, if the light parts of the picture look fairly dark on the negative, then the print was poorly exposed, and should be made over (if the whole negative is very dark, then you overexposed the film.  It may or may not be salvageable).  Politely explain to the person at the counter what you want.  One advantage of dealing with a one hour lab is that each exposure is looked at by a human operator, who can bias the exposure for this type of situation.  A second advantage is that problems can be resolved faster.

  Photographing your monitor screen is not difficult, and the results can be quite rewarding.  By simply taking a little care you can get photographs that will put the best output from your dot matrix printer to shame.  And best of all, it's fun.


About the Author__________________________________________

  Ted O'Hara is operations manager of a chain of one hour photo labs in the Boston area and has been photographing video screens off and on for several years.  If you have any questions or comments about this article, please send E-mail to Ted38