Community Matters

This seems to be a feature that doesn’t get a lot of attention – but I think it’s widely underestimated. Nikon DSLRs like the D300, D700, D3, D3x, D90 (and many of the older ones – but I don’t know exactly when this started) allow you to use the ISO sensitivity like a third parameter when calculating exposure!

Traditionally people think of the ISO value as fixed (I guess this comes from the day of using film that has a given ISO value) and then look for a matching f-stop and shutter speed that creates correct exposure.

The f-stop is limited by what your lens has to offer. f/1.4 or 1.8 on a fast prime lens like the 50mm/f1.4. f/2.8 on an expensive zoom like the Nikon 24-70mm/f2.8 I played with last weekend. Or something slower like f/5.6 on the cheap “kit lenses” most cameras get sold with.

And the shutter speed is limited by the slowest speed that you can take a picture at without it getting fuzzy because of the jitter of your hands. In the old days people used the rule of thumb of 1 divided by the focal length of your lens (so 1/50s for a 50mm lens, etc). Today with VR you usually can push this quite a bit slower – I often take shots at 1/50s with a 200mm lens.

But what do you do if you are in a low light situation? Indoors without flash, in the shade, at dawn, etc? Well you could of course increase your ISO value, but likely you’ll get it wrong. And if you crank up your ISO too high you get too much noise, but if you don’t go high enough, your shutter speed will be to slow and you will get a picture that isn’t crisp. Oh and this of course takes time and attention and you risk losing that perfect shot you’ve been waiting for.

The solution: auto-ISO. Here you can tell your Nikon the slowest shutter speed you are willing to allow. And you set your ISO to a reasonable value that gets you low-noise pictures (I tend to have it at ISO200). Then as long as there is enough light, you’ll get the best possible picture at ISO200. But once it gets darker, instead of forcing a slow shutter speed, the camera increases the ISO in order to keep the shutter speed no slower than the value that you picked. I much rather take a picture at maximum aperture, 1/50s and ISO800 than at 1/12s and ISO200. The first one will be nice and crisp, the second one is almost certain to be fuzzy due to the jitter of my hands when taking the picture – and potentially the movement of my subject.

Is this a miracle cure? Of course not. At some point it’s just too dark. Depending on the camera you use, there’s an upper limit to useful ISO values. A D300 takes great pictures up to about ISO1000 (some noise, but easy to deal with). A D3 or D700 allows you to go all the way to ISO3200 and still be happy with most pictures. But once you go beyond that, you’ll still get noisy pictures.

But this still adds something like 3-4 more f-stops to what you can do with your camera without this (and without having to manually change the ISO setting – which likely means you’ll miss the shot).

Try it out!