Cameras Should Have Three Legs

By Ken VanBree

If you have already bought a digital camera to document your construction progress, you may be looking for the next piece of equipment that you can buy to improve the quality of your pictures. I would like to put in a plug for an underused tool that you might already own, namely a tripod.

Digital cameras come in many weights and sizes, but they need a fair amount of light to record an image properly. The equivalent film speed on most digital cameras is around 50 ASA. This means that in bright sunlight you can properly expose an image at an aperture of f16 and a shutter speed of 1/50 sec.

Using a normal or wide-angle lens, a shutter speed of 1/50 sec is fast enough for most people to shoot hand-held without inducing motion blur. Some people have a steady enough hand that they can get acceptable images at lower shutter speeds, but a good rule of thumb for normal and wide angle lenses, is don't shoot hand-held at shutter speeds below 1/50 sec.

When using a zoom lens, this minimum acceptable shutter speed goes up roughly by the zoom factor. A Canon G3, for example, has a zoom ratio of four. This means that when the lens is zoomed out to its maximum telephoto setting, you will need to use a shutter speed four times faster (that is, 1/200 sec) in order to shoot hand-held without motion blur.

But the interior of homes under construction are seldom as brightly illuminated as outdoor scenes in sunlight. Inside lighting levels can be anywhere from 7 to 12 f-stops below the outdoor level. It may be a bright and sunny day outside, but the inside of an interior bathroom may be darker than a witch's lair illuminated by a single candle. In order to get an acceptable image, you'll need either additional lighting, or use a shutter speed longer than 1/50 sec, which means you'll need to use a tripod.

You may think you could increase the film speed to deal with low light situations, but the concept of film speed in digital cameras is a ruse, a case of digital trickery akin to digital zoom. Increasing the film speed on a digital camera actually reduces the amount of light that falls on the sensor. Digital cameras make up for the lack of light by post-processing the image to bring out detail that would otherwise be lost in the shadows. In a brightly lit scene, the results may be acceptable, but in a dark room you will lose detail.

Using your camera's flash is no panacea for dealing with low-light situations. The light from a flash falls off as the square of the flash-to-subject distance. Although objects four feet away from your flash may be properly exposed, objects that are 16 feet away will appear to have fallen into a black hole because they will receive 16 times (four f-stops) less light from the flash.

The lowly tripod is an underused tool in construction photography. It is the most reliable way to ensure that your images are sharp and properly exposed, even if you are photographing that lair by candlelight.

September 2005 Builder Architect Edition Issue

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