What really matters in digital Photography, part 2

3. Important for many more people than you'd think: sensor size

Yes, that's sensor size. Yes, that sounds like "hardware details I don't care about". But did you ever wonder why all those digital cameras offer ISO settings 50, 100, 200, 400, where 400 and even 200 are completely unusable because they create an ugly noisy mess of a photo?

Left: small part of a grey sky, Canon EOS 300D at ISO 400
Right: small part of an evening sky, Canon Powershot S2IS at ISO 400
Notice all the unwanted specks and dots of the right part?

And have you ever seen an ISO 400 shot of a DSLR? If yes, believe me, you'd want one from that point in time. The reason is that the sensors of all normal consumer cameras (including the "mega zoom" ones like the S2IS, S3IS, ...) are TINY. Hardly ever a photon makes the way into these sensors in the evening :-). But the actual sensor size is typically not mentioned in tech specs of cameras, and actually I did not know for a long time that all my cameras have sensors that have 13 times less sensor area than those of DSLRs. Yes, 13 times. 13 times less light will hit a sensor of my S2IS in 1/60 of a second than it would if I had a DSLR.

"Why do I need to care about that?" you ask? You need the higher ISO levels in situations when there is less light available as on a bright day. Example: pictures in churches, evening snapshots, forests. Less light hits the sensor, and either you crank up the ISO setting, or you live with dark photos, hoping that Photoshop will recover most of the details (and believe me, that little flashlight that cameras feature are the best way to make ugly photos. As I've never made a good photo with a built-in flash and I've never seen anybody else managing this I've plainly given up on those flashes).

Some consumer cameras like my S2IS have image stabilizers to compensate for some of this - I can take good photos down to 1/13th of a second with my S2IS. But then, people tend to move around, and in 1/13th of a second, they move more than you think...

Martin Luthers Grave in Wittenberg, Germany
With image stabilization, people look like ghosts.

Additionally to the pure ISO noise issues it seems to me that typical problems of small digicams like "purple fringing" are mostly caused by the small sensor's. I've never seen all those frustrating effects in DSLR images.

Unfortunately, sensor size is more or less the same with all non-SLR cameras. Either you get a small, convenient camera with a tiny sensor, or you get a big, expensive SLR that is painful to carry around with a much larger sensor.