ISO
If you shoot a lot of film, you’re probably already used to considering ISO when you buy film for a shoot. Just as with film, ISO on a digital camera is a measure of how quickly the camera’s sensor can gather light. A higher ISO means a “faster” sensor — one that requires less time to gather a given amount of light. However, as with film, higher ISOs generally result in noisier images.
Another strength of digital photography is that you don’t necessarily have to commit to a given ISO for a large number of shots. Because you can change the ISO for every shot you take — as if you were shooting sheet film — you can think of ISO as yet another exposure parameter.
For example, say you’re taking a handheld shot of a flower at ISO 100 and you want to use a narrow aperture for deep depth of field. Unfortunately, it’s cloudy out and your light meter has recommended a shutter speed of 1/15, which is much too slow to shoot without a tripod. Rather than open up your aperture and risk compromising your deep depth of field, you can simply boost the ISO to 200, allowing you to shoot at a more manageable 1/30th of a second. Because you can always change the ISO back to 100, you don’t have to worry about pushing the exposures of all the shots in your camera.
If your camera offers adjustable ISOs, it probably offers a range of speeds from 100 to 400. Higher-end cameras will offer faster speeds, some as high as 6400. It’s important to do some tests of your camera’s faster speeds to get a feel for how severe the increase in noise might be. For example, you may find that any ISO above 400 with your camera simply produces unacceptably noisy results.
Your main concern when changing ISO is to remember to change it back if you’ve changed speeds for a particular circumstance.
The top image above was captured with an ISO of 90. The camera captured the second image with an ISO of 360.
Aberrations
Remember that when you buy a digital camera you’re effectively buying a single roll of film that will never be used up. Just as you need to learn about the color characteristics and qualities of a particular film, you’ll need to do some experimentation to learn about the color tendencies of your particular camera.
Plan on shooting a lot of test shots to determine overall color characteristics. Does the camera shoot with a color cast in certain lighting situations? Does it render some colors more accurately than others? You might also want to contrive some trickier tests. For example, many digital cameras have trouble defining edges when the edges of a target object fall on the border of bright background colors. Also keep an eye out for noise. Can the camera render shadow details smoothly and cleanly?
If you’ve been shooting with film for any length of time, you may have encountered chromatic aberrations in your film camera. These strange color artifacts that appear as odd-colored fringes are caused by a lens’ inability to evenly focus all wavelengths of light. Digital cameras are susceptible to the same problems, though most decent digital cameras include optics of sufficient quality that these aberrations are uncommon.
However, 2- and 3-megapixel cameras are prone to a weird purple fringing that looks like chromatic aberrations. Opinions differ as to the cause of the artifact, but most people agree that the trouble only occurs when shooting into a high-contrast scene when using your camera’s full wide angle and a large aperture (or, if you’re using a very long lens, full telephoto). Consequently, it’s usually landscape shots that exhibit this problem the most.
If you find yourself in such a situation and you know your camera is prone to purple fringing, consider zooming in a bit and using your camera’s manual controls to go to a smaller aperture. Purple fringing often only occurs on the edges of the frame, so you might consider re-framing to locate troublesome areas closer to the middle of your image.
Depth of Field
As you probably already know, depth of field in an image is a function of aperture size and focal length. The larger the aperture (the smaller the f-stop number) and longer the focal length, the less depth of field your image will have. Most digital cameras, though, are very small, with lens focal lengths measured in just a few centimeters. Consequently, it’s very difficult to shoot images with very shallow depth of field. In many cases, the large depth of field is great because it means your image will be well-focused and sharp. If you want to intentionally blur the background of an image, though, be aware that you may not get as shallow a field as you’re used to.
Latitude
Finally, most digital cameras perform very much like traditional slide film. If you’ve got a lot of experience shooting slides, then you’re going to feel right at home with the exposure needs of a digital camera. Just as most photographers typically underexpose slide film by about half a stop when shooting in daylight, you’ll probably find you get better color results if you crank your digital camera’s exposure compensation down by 1/3 to 1/2 of a stop. Unfortunately, digital cameras have about the same latitude as slide film which means they don’t offer a wide margin of error for your exposure calculations.
Don’t Be Afraid!
There’s no reason to let any of these new concepts scare you away from digital photography. As you’ve seen, though, there are some new things to think about and some new habits to learn when you make the switch. Given some time, you’ll likely find that these new concerns quickly become part of your normal shooting mindset.
This article was last modified on December 14, 2022
This article was first published on April 17, 2001
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