Managing Digital SLR Quirks

Some differences exist between a digital SLR (dSLR) and a non-SLR camera. Whether you call them quirks, idiosyncrasies, or foibles, most of these differences, like the faster operation and lack of shutter lag, are advantages that you can benefit from. Others, such as lack of an LCD preview, are things you must simply get used to. But other dSLR quirks command a bit of your attention. The three most demanding idiosyncrasies are detailed in the following sections.

Understanding noise

If you date back to the film era, you might recall that film came in various speeds or sensitivities, represented by ISO ratings. (ISO is the name chosen by the International Organization for Standardization, but it isn't an acronym.) You probably purchased an ISO 200 film for everyday use and perhaps a "slower" ISO 100 product when you wanted a less grainy picture or because you believed these films provided better quality.

Digital camera sensitivity is measured in ISO-equivalent settings, too, but, in truth, each digital sensor has only one actual ISO sensitivity — usually the lowest setting available for that camera. This minimum ISO setting varies from ISO 50 to about ISO 200, depending on the camera. All other ISO settings are created by amplifying the signal captured by the sensor, so photons that were almost too dim to register are electronically beefed up to become full-fledged pixels.

Unfortunately, at the same time, nonphotons are mistaken for true pixels and assigned pixel-hood even though they don't deserve it. These bogus pixels are what photographers call noise. Noise appears in your pictures as multicolored flecks that look like grainy, irregular dots.

You need to figure out how to use your camera's noise reduction (NR) features to reduce problems like those shown in Figure 1. Depending on the model you own, NR may be applied automatically to high ISO settings but be optional for longer exposures.

Getting the real dirt on sensors

It might take a while, but eventually you'll get some dust on your dSLR sensor and will need to clean it. Don't panic! The process isn't difficult or dangerous, but you can take the following steps to minimize the number of times you'll have to clean your sensor:

• Minimize dust entry. If you point your camera downward when changing lenses, dust particles are less likely to settle into the mirror compartment.

• Don't provide dust with a safe haven. Make sure that the mounts of your lenses and the rear lens elements are clean and dust-free when you attach a lens to your camera.

• Think clean. Try to change lenses in relatively clean environments. Avoid dusty rooms or gusty outdoor locations.

• Minimize the time your camera is lenseless. Have your new lens ready to mount as soon as you remove the old one.

Going in crop-factor circles

Many digital SLR cameras use a sensor that is smaller than the 35mm film frame. Even so, most vendors rely heavily on lenses that were originally designed for these full-frame film cameras.

That means that if you cut your teeth on 35mm cameras, the apparent focal lengths of your dSLR camera's lenses are likely to seem "wrong" to you. The smaller sensors cause the image to be cropped, so a 50mm "normal" lens becomes a mild telephoto. A 105mm "portrait" lens that you used to take head-and-shoulder shots with a film camera might not be such a good choice for portraits anymore.

And, of course, your wide-angle lenses might not be so wide when cropped by your sensor. This effect is sometimes called, inaccurately, a multiplication factor or lens multiplier because the easiest way of representing the effect on the camera's field of view is by multiplying the focal length of the lens by the factor. A 100mm lens "becomes" a 150mm lens with a camera that has a 1.5X crop factor.

Of course, in truth, no multiplication is involved. That 100mm lens is still a 100mm lens and has the same depth of field. Your 180mm f/2.8 optic isn't magically transformed into an amazing 360mm f/2.8 super-telephoto. You could get the same effect by shooting a picture on a full-frame camera and then cropping it down. That's why the correct terminology for this effect is crop factor. Common crop factors with today's dSLRs are 1.3X, 1.5X, 1.6X, and 2X, as shown in Figure 2.