I’ve been spending a lot of time with digital cameras lately – reviewing models from most major companies. After all this, the topic most on my mind is pixel noise – speckle artifacts that especially show up when you shoot at high light-sensitivity (ISO) settings.
My somewhat-scientific conclusion: A bigger sensor is really worth it.
I’m not talking about the number of pixels. (In fact 5-6 GOOD megapixels are plenty.) I’m talking about the physical size of the sensor. While working on a camera buying guide for the New York Times (Just the Right Digital Camera for You), I shot many identical scenes at the moderately high sensitivity of ISO 400 – which you might use on a cloudy day or in a dimly-lit room (if you want to avoid the harsh glare of a flash). I tested quite a few cameras, but picked just four shots here to illustrate. The easy winner, to my eye, is the Canon Digital Rebel (photo above). This is the first generation of the camera: 6 megapixels with the original Digic processor.
I put it up against two other Canons – the 5-megapixel SD400 (top) and the 7-megapixel SD500. (I’ll never understand Canon’s naming scheme.) Both cameras have the Digic II processor – which is better at taming pixel noise than the original Digic. But you can compensate only so much for what the sensor gives you. (Geeks among you may know, or want to know, about another difference: Canon SLRs use CMOS sensors developed by Canon, while their other cameras use CCDs sourced from other companies, like Sony.)
Just so you know, we are talking about a BIG difference in size between SLRs and pocket cams. For example, Canon’s SD500 has a 7 megapixel sensor that measures about 9 millimeters diagonally. The new Digital Rebel XT’s 8-megapixel sensor measures 17 millimeters.
So what does this all mean? If you are really going for top quality, image sensor size is critical. And don’t assume that a big camera has a big sensor. The new Panasonic FZ30, for example, is a hefty, SLR-style enthusiast model, but its 8MP sensor is the same size as the sensor in the Canon SD500 – and it has to fit an extra million pixels in the same space. I used it for a day and found the photos QUITE noisy. (Another reviewer had similar impressions, by the way.)
Now, pocket cameras aren’t bad, in the right circumstances. The SD400, SD500, and T33 are among the best pocket cams out there. With a lot of light (or flash) and moderate print sizes (say up to 8.5 x 11 inches), you can do quite well with them. And they are more than adequate for little party shots that you will post on a Web site.
But if you are trying to do real art photography, you need a camera with a really big image sensor (most likely an SLR). And whatever type of camera you are buying, it’s good to find out what size sensor it has. Unfortunately, the nomenclature camera makers use to describe image sensor size is medieval in its obscurity. But this guide helps you translate it.