I’ve been reading reviews about DSLRs on various websites and noticed that some devote several pages to image quality at ISO 1600, 3200, 6400 and above. Now that I’m ready to trade up from a digicam to a DSLR, should I be really concerned about the quality at ISO 6400, for example? When I was shooting with a 35-mm SLR, I mostly used ISO 100 to 400 film and, on a few occasions, Fujicolor 800. So why is ISO 3200 or ISO 6400 so important now?
Your question makes a valid point, Samantha. In conventional photography, few of us ever used the very “fast” films. In fact, most retailers did not even stock print film faster than ISO 800 or slide film faster than ISO 400. But since digital SLRs have offered built-in high-sensitivity options—often up to 12,800 or even to ISO 102,400 now—this aspect receives a great deal of attention. And that’s not surprising, since high ISO quality is one obvious aspect that can be useful when comparing various cameras.
Consumers have come to expect full coverage of high ISO quality, even if it’s not one of the primary criteria for deciding which DSLR is “best.” Especially today—when an increasing number of cameras and lenses are equipped with an image stabilizer—we rarely need to use an ISO above 1600. That level provides an adequately fast shutter speed to prevent blurring from camera shake in most low-light situations. In my own photography, I’ll switch to ISO 3200+ only when shooting indoor sports such as basketball or volleyball. In such situations, it is essential for a fast shutter speed to freeze the competitors’ motion, and it’s great to have a camera that provides fine image quality.
Unless you intend to frequently photograph moving subjects in low light—or to shoot in unusually dark locations without flash or a tripod—you should be more concerned about other issues. That should include continuous (tracking) autofocus performance, burst speed, the accuracy of exposure, white balance and focus, image quality at your most frequently used ISO levels, the ease and the logic of a camera’s operation, etc. Since reviews also cover those aspects, simply concentrate on the most relevant sections of any test report instead of getting bogged down in comparisons of ultra-high ISO quality.