alan little’s weblog

shades of grey

2nd May 2005 permanent link

I thought http://www.dantestella.com/technical/dynamic.html

Which turns out to be about 6 stops: 3½ under, 2½ over.

The mid grey bar with the red stripe shows a grey card at a standard exposure. The bars to the left and right show under- and overexposure in 1 stop increments. We go white - highlights completely burned out – somewhere between +2 and +3 stops.

If you compare the response curves of the D200 and the D70, you can see clearly that the D70 is flatter, less contrasty in the 2 to 3 stops underexposure range; but whether this is intentional or not, it then drops abruptly to the noise floor at -4. Look in comparison how the D200 has a little more midrange contrast, then tails off in a perfectly smooth s-curve to black at 5 stops under. Beautiful.

The D70 is getting noisy at -3, and has basically disintegrated into noise at -4. The D200 is tightly contolled, almost completely noise-free, right down to black at RGB 2,2,2.

Custom white balance is even more accurate than the D70 – red values are slightly high on the D70 shots; the D200 ones are absolutely neutral.

The D200 is in most ways my dream camera: superb handling and build quality, excellent colour rendering, more than enough resolution for anything I’m likely to want to do for the foreseeable future. (Serious landscape photography and small children don’t combine well). But dynamic range continues to be the big achilles heel of digital sensors compared to (some) film.

I don’t know enough about the physics of digital sensors to know if this is actually a Hard Problem that isn’t going to get much better because we're already up against a physical limit (which seems from what I read to be pretty much the case with pixel pixel size and resolution); or if it’s just that nobody has paid enough attention to it yet. I know Fuji and Kodak have tried to address it, with very limited success.

Fuji’s S3 – successor to their S2 that was much loved by portrait and studio photographers a couple of years ago (I was seriously considering buying one, but then Nikon came up with the D70) – uses a sensor with large and small pixels. The large ones give you low light sensitivity; if there’s too much light and they’re blown out you can then try to get a reading from the less sensitive small ones. Or something like that. Interesting idea: from the reviews I read, such as this one b Thom Hogan, it doesn’t seem to have worked very well. Apparently in the right circumstances, if you’re really careful, you can maybe squeeze out an extra half a stop compared to a good conventional sensor. To make a compelling difference it would have had to be two stops easily.

Then there is, or was, Kodak. Kodak’s recently discontinued digital SLRs had a reputation for being deeply flawed and difficult to use, but capable of wonderful results in the hands of the few who made the effort to learn how to use them effectively. One of those eccentric few, and generally one of the web’s most interesting offbeat photography writers, is Dante Stella. In his fascinating comparison of the kodak with Nikon’s current über-camera, the D2X, he says Kodak, although they use a normal sensor, have software that is highly optimised for squeezing as much dynamic range as possible out of the signal coming from that sensor. The result, he says, is that shooting the Kodak is like shooting negative film whereas the D2X’s response is more like slide film: punchier straight-out-of-the-camera images, but less forgiving.

I also used to shoot a lot of colour negative film, particularly Fuji’s lovely Reala, on the basis that that too has tremendous exposure latitude and can shoot more or less anything without losing highlight or shadows. This didn’t actually turn out particularly well - the resulting low contrast negative captured vast amounts of raw information, but turned out to be an absolute bastard to process digitally to get decent colour balance and contrast. I’m not the only person that has been down this particular road either.

related entries: Photography

all text and images © 2003–2008