How to Photograph Video Screens

Copyright 1989, Tom R. Halfhill

[ GOVERNOR MICHAEL DUKAKIS ]

Because of the slow shutter speeds required (1/15 second or slower), the best way to capture TV broadcasts is to wait for a lull in the action. (All photos in this article were made with a Canon SLR and Canon FD 35-70mm f/3.5 zoom lens at 70mm.)

If you've ever tried to photograph a video image on a television screen or computer monitor, you may have been disappointed with the results. Maybe you're trying to capture historic moments from TV broadcasts, create slides of computer-generated charts for a business presentation, or even record proof of a high score on a videogame. To get good results, there are several tricks involved that aren't difficult to master, but that also aren't immediately apparent without a lot of trial-and-error shooting.

Over the past several years I've photographed hundreds of video screens for publication in a variety of books and magazines, and along the way I've probably committed every mistake imaginable. To save you the trouble of repeating them, let's cover some of the basics.

The equipment you'll need really is basic: a camera, a tripod, and a cable release. Almost any type of camera will do, but a single-lens reflex (SLR) is preferred -- you'll be working at fairly close focusing distances, and exact framing is important. Cameras with separate viewfinders will do the job, as long as they can focus closely enough to fill the viewfinder with the screen without parallax error.

For best results, the camera should also have slow shutter speeds in the range of 1 second to 1/15 second. Of course, some of today's automatic cameras don't let you control the shutter speed or even tell you what speed the camera has selected. For this reason, a fully manual camera -- or an automatic camera with manual override -- works best.

The tripod should have precise leveling adjustments, and the cable release should be long enough to isolate the camera from minute vibrations when you press the plunger. Many of today's computerized cameras have electronic cable releases that are truly vibration-free (although they also cost more than regular mechanical releases). If you don't have access to a cable release, sometimes you can make do with the camera's self-timer, but this will obviously be a problem if the video image you're photographing is changing unpredictably (as is the case with TV broadcasts).

One piece of equipment you won't need is your flash unit. The harsh glare of the flash would either drown out the video image or obscure it with annoying reflections.

What type of film should you choose? Some people automatically reach for a high-speed film in the ISO 400 range, figuring that they'll need the speed in the absence of a flash. But actually, video images are pretty bright, and ISO 100 is plenty fast. Anything much faster than ISO 200 is really too fast. Color print film, slide film, and black-and-white all work fine.

Preparation is Everything

The first thing to do before taking pictures is to prepare the room and set up the camera. This is where most people who try to photograph video screens make their first mistakes, because they don't appreciate how much care must be taken to eliminate screen reflections and line up the viewfinder. Reflections caused by room lights and windows that you probably don't notice when you're watching TV or looking at a computer monitor will definitely not be ignored by the camera. Even the so-called "non-glare" screens have hot spots.

To erase them completely, the room must be darkened. This doesn't mean you have to turn your living room or office into a darkroom suitable for developing film, but it does mean you need to close all the window blinds and drapes, and shut off all the room lights. If the room has a door, close that, too. Examine the screen carefully -- it must be completely free of reflections and shiny spots.

When you're certain that this problem is solved, turn on the lights and set up your tripod and camera. Again, this requires more care than you might guess. The most common mistakes are to position the camera too far from the screen, and to set it up with the image out of kilter. Move the camera close enough to the TV or monitor to completely fill the viewfinder with the picture.

Be aware that video screens are rather squarish rectangles, so you'll have unavoidable dead space on either side of the screen if you're using a 35mm camera (which has a considerably wider rectangular format). With a 6x6cm (2-1/4 inch square) camera, you'll have to leave some dead space at the top and bottom of the screen instead of the sides. The 6 x 4.5cm format has almost the right proportions. In any case, the dead space surrounding the screen will record as black in the finished photo if the room is sufficiently dark.

Most of all, pay fanatic attention to the alignment of the camera with the screen. The lens must be centered exactly on the screen, and the surface of the screen must be parallel with the front element of the lens. Some screens -- particularly computer monitors -- are tilted slightly backward, and some are tilted back even though their protective front glass cover is not. Compensate for this by tilting your camera slightly forward on the tripod.

Proper camera alignment is extremely important, because otherwise you'll get a distinct "keystone effect" -- the photographed screen image will appear to be wider at the top or bottom or one of the sides. To aid in your alignment, it sometimes helps to compare the TV or monitor's bezel (front frame) with the edges of your viewfinder. But keep in mind that a monitor with a sloping screen might have a perpendicular bezel, which could fool you.

To confirm that your alignment is just right, darken the room and check the viewfinder again. The picture should be squared up exactly.

[PHOTO LINK #1: If the camera and tripod aren't carefully aligned, you'll get a keystone effect like this. Notice how the screen is wider at the top than at the bottom.]

You may notice that the edges of the video image are slightly curved. Almost all video tubes have some curvature, although it's remarkably slight on the latest "flat-screen" models. You can flatten out a little of this curvature by using a longer-than-normal focal-length lens. When shooting with a 35mm camera, I prefer a portrait-length telephoto in the 70mm to 105mm range. If you try to use a lens much longer than that, you'll probably find yourself backing into some furniture or a wall.

Clean the Screen

The final step before taking pictures -- and a step that's often overlooked -- is to prepare the screen itself. First, thoroughly polish the screen with an ammonia-based glass cleaner. You'll probably be surprised how much dirt comes off. If anyone regularly smokes near the screen, you'll really be surprised. The static electric charge of a video tube attracts tobacco smoke like a magnet, and the result is an ugly gunk that's guaranteed to foil the best-quality lens. (Not to mention what it does to your lungs.)

Next, darken the room and carefully observe the screen you're about to photograph. Since it is normally adjusted for room lights, it probably looks too bright when the room is dark. The best way to adjust it is to gradually turn down the brightness and contrast controls while watching a black area of the picture. When the black area goes totally black -- in other words, when that part of the video tube shows no glow at all -- the picture brightness should be about right.

If you're photographing a color screen, adjust the color controls as you normally would. Video tubes tend to be a little bluish, but this is hard to detect with the naked eye. If your photographs end up looking a bit too blue, you might want to compensate in the future by turning down the blue tint just a hair, or by using a slightly warm color-correction filter over the lens. Actually, you probably won't notice the bluish effect at all unless you're using color slide film, and sometimes you can compensate merely by switching films -- say, by shooting warmish Kodachrome instead of coolish Ektachrome.

Now you're ready to determine the proper exposure. You can rely on the camera's built-in meter to accurately measure the exposure for you. In my experience, even a full-field averaging meter won't be too misled by the surrounding dark areas if the screen adequately fills the viewfinder. A narrow-field spot meter, however, will definitely be fooled if it's aimed at an uncharacteristically bright or dark part of the picture. If your camera allows you to select metering patterns, pick a center-weighted or averaging mode.

If you're using a handheld meter, aim it along the lens axis and hold it close enough to the screen to ignore the surrounding darkness. But don't hold it so close that it acts as a spot meter on an isolated part of the picture. If the picture consists of large dark areas punctuated by small bright zones -- monochrome computer monitors with text displays are particularly a culprit here -- fill the screen with a more evenly illuminated image before taking your meter reading.

Setting the Shutter Speed

This is where a fully manual camera, or an automatic camera with manual override, is a real boon. Somehow you need to set a shutter speed no faster than 1/15 second when photographing a TV picture, or 1/4 second when photographing a computer monitor. Why? Because of the way a TV or computer displays an image on a video tube.

Rather than digressing into a lengthy technical explanation, suffice to say that the picture we see on a video tube doesn't really fill the entire screen at any one instant. Instead, the image is continuously "painted" on the screen in "frames" that last for a duration of only 1/30 second. Thanks to the slow-fading glow of the video tube, and the persistence of vision of our eyes, we perceive the image to be constant. But if you photograph the screen with a fast enough shutter speed, the camera captures only part of the fading image. The fading portion appears as a horizontal band across the photo. The width of the band varies with the shutter speed. To avoid this effect, you need a slow enough shutter speed to ensure that at least one complete frame has been painted on the screen.

[PHOTO LINK #2: If the shutter speed is too fast, a dark horizontal band mars the photo. Slow shutter speeds eliminate the band and also help mask any wavy-line interference patterns.

That's why, to be absolutely safe, you need a speed no faster than 1/15 second when photographing TV broadcasts. Computer monitors are another matter. Because of technical differences in the way computers display video images, I've found that 1/4 second is the fastest safe speed with most personal computers. (Incidentally, there is no limit on how long the exposure can be, other than reciprocity failure of the film.)

[PHOTO LINK #3: Most computer screens require even slower shutter speeds than TV broadcasts -- no faster than 1/4 second.]

Of course, one problem when shooting at slow shutter speeds is that you'll get a blur if the screen image is moving. When photographing TV broadcasts, usually you can time the shot during a lull in the action. If you absolutely must photograph a moving picture, one solution is to tape the scene on a videocassette recorder, play it back, and pause the tape at the appropriate moment.

This trick also works with some personal computers that have composite video outputs that are compatible with a VCR's video inputs. But to get acceptable results, you need a VCR that has a separate special-effects head. VCRs with multipurpose play/record heads don't have a clear enough picture in freeze-frame mode.

When attempting to photograph fast-moving computer screens and videogames, check to see if the program has a pause function. Most do, although they might display an unsightly "PAUSE" message across the screen.

Proper Exposure

In my experience, a properly adjusted color TV or computer monitor calls for an exposure of about 1/4 second at f/11 or thereabouts with ISO 100 film. I usually shoot Ektachrome 100 and bracket the metered exposure by plus and minus one stop. If, for some reason, the screen picture is unusual and I'm really in doubt, I'll bracket plus and minus two stops as well. But 90 percent of the time, a one-stop bracket results in a good photo, once you refine your technique.

For publication, you should generally pick the frame that's a little lighter than the one you'd choose for making a print or projecting a slide. Photos tend to gain some density in print (unless the publication uses National Geographic-quality paper).

If you don't want to photograph the entire screen, you can move in as close as you want to frame just a portion of it. However, you'll probably find that the limitation here isn't the close-focusing range of your lens, but rather the resolution of the screen. Video images are composed of thousands of tiny dots (called pixels, for picture elements), and the image begins to break up fairly quickly at macro-focusing distances.

For best results, even when photographing the entire screen, use a smaller TV or monitor rather than a larger one. I've found that 19-inch screens are just about the upper limit, and a 12- or 14-inch screen is even better. Apart from sharpness considerations, the larger screens are also difficult to photograph in small rooms, especially when using longer lenses.

[end]


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