Digital Camera Master

All that talk about f/stops, shutter speed, and ISO settings may seem irrelevant to your digital camera, but it’s not—all cameras use these concepts, even though they’re sometimes disguised fairly well. The main difference between a digital camera and a chemical film camera, of course, is the fact that digicams don’t use film. That means you never load anything that has a specific ISO value into the camera. So how does the camera actually work?

Simple. When light enters the camera at the moment of exposure, it doesn’t hit light-sensitive silver halides that are fixed in a chemical broth. Instead, the light hits a computer chip called a charge coupled device (CCD). The CCD is light sensitive, and each of its many pixels register changes in light just like the film’s many grains of silver react individually to light. In other words, the silver grains in film and the pixels in a CCD are essentially the same thing. They contribute to your picture in the same way, and both are the smallest components that make up your picture. The CCD makes a picture by noting the variation in light rays that travel through the camera lens. The CCDs pass this information on to the camera’s microprocessor in the form of varying electrical charges. The image is transformed into digital bits and stored on a memory card.

Your camera’s CCD functions like the film in a 35mm camera, except that it differs in one important way—you can’t swap the CCD out of your camera and insert one with more light sensitivity for low-light photography. The CCD is a permanent part of the camera. Camera makers understand that you might need to change the camera’s light sensitivity on occasion, though, and that’s why many cameras can have their ISO rating “adjusted” on the fly, whenever you want. In essence, what this does is allow you to “turn up” or “turn down” your camera’s sensitivity to light.

Use ISO for Exposure Control
You can use the ISO control built into your digital camera to vary its sensitivity to light and thus mimic the effect of using different grades of 35mm film. This can come in handy in a number of situations, such as when you’re shooting in particularly high or low light levels. Remember a few key facts about your camera’s ISO ratings, though:

It’s not a real ISO adjustment, in the sense that your camera doesn’t have real film. Each camera maker has a somewhat different way of implementing this feature, but they all use ISO numbers since that’s comparable to 35mm film, which most people are at least a little familiar with.

Don’t leave your camera set at the highest ISO all the time. Some folks think that by setting their cameras to the highest sensitivity, they’ll be prepared for anything and won’t have to muck with the camera menu when they’re on the go, trying to take pictures. In reality, boosting your CCD’s sensitivity to light also increases the amount of digital noise you’re capturing. More ISO means more fringing, artifacts, and digital detritus. Sometimes that’s unavoidable, but stick with the lowest ISO value you can get away with most of the time.

Change the ISO Setting
If you find yourself in a situation in which the lighting isn’t quite right for your picture, it’s time to bump up the camera’s ISO value. Remember that not all cameras come with ISO adjustments, so review your user manual to see if this applies to your particular model.

Here are some situations in which you might need to increase the ISO:

You’re shooting in a low-light situation, such as early evening or indoors Naturallight photos have a certain appeal, and by increasing the light sensitivity of your camera you may be able to shoot a picture without using the flash at all. Using natural light can eliminate harsh shadows and produce more natural colors.

Your subject is too far away for the flash to have any effect During the day you might be outdoors and want to take a picture of something, but there’s not quite enough light—such as in winter or during very overcast conditions. Your camera wants to use a flash, but your subject is just too far away. The flash on your digital camera has a very limited range. So to properly expose your picture, you need to use “faster film”—that is, increase the camera’s ISO setting.

You’re shooting at night Most digital cameras have very little ability to take pictures at night or in near total darkness. A few models can extend the shutter to about half of a second, but that’s about it. As a result, if you want to capture anything at all with a night shot, you’ll need to increase the camera’s light sensitivity to maximum.