HI-SO!

It seems half the history of photography has been spent on trying to make pictures in low-light conditions. Starting out with wet plate cameras that took several minutes to make an exposure to ‘pushing’ film speed beyond its manufacturer’s rating. When digital entered the world the hunt continued, with the first electronic cameras having no greater sensitivity to light than standard films. Now it is quite common to have ISO ratings up to 6400, or even higher. But how good are they?

The first caveat of this experiment is: your actual results may vary.

To check out how good these upper ratings really are I grabbed my “go-to” camera (Nikon P610) on a dark night and shot an impossible scene using automatic exposure on all the “high” ISO indexes available: 400, 800, 1600, 3200, and 6400. All of the images were “too dark” on purpose, and the details brought up in post-processing to see what lay beneath. The results I got did not surprise me as earlier shoots had given a fair indication of what to expect. In short, they come up short.

We expect an increase in noise at higher ISO sensor settings just as we expect an increase in grain with higher ISO film speeds. Chromatic aberration gets exaggerated. Image quality degrades. No one should expect anything different. But just how bad is it? Consider:

The two lowest ‘speed’ images, 400 & 800, give the most well-defined results. This despite the fact they would have had larger aperture and/or longer exposure time. What’s more there isn’t a steady decline in quality as the ISO increases. Instead it drops off drastically with the one stop change from 800 to 1600.

You could argue about how better results could be obtained by controlling either aperture of shutter speed, but that isn’t the point. The point is when it comes right down to it there is an upper limit to how sensitive the sensor really is to light and no amount of technological trickery will get around that. On this¬†particular camera the limit seems to be ISO 800.

Now to be fair I’ve shot some pictures at the same ISO ratings but during cloudy daylight so you can see how the ‘speeds’ compare under tolerable lighting conditions:

The first two, 400 & 800, are nearly identical – which is what we’d expect and want. When the ISO is shifted up to 1600 the exposure is still pretty good but there is a noticeable loss of detail in the image. 3200 & 6400 continue with the detail loss but also show clear signs of over-exposure, something that digital cameras don’t deal with well.

So for this camera, the Nikon P610, there is no point using an ISO above 800. Most of the time 400 is more than enough, and frankly since I tend to shoot still subjects in bright light even 200 is more than I need. I suspect my Canon handles high ISO better, and may be worth experimenting with it to find out. It does have specific noise cancellation settings for both high ISO and long exposure, but other than increasing processing time I haven’t noticed any particular improvement from using them in normal shooting so far.

Addendum: I did test the Cannon and found it does not suffer from the “sudden drop off” of quality in extreme low-light shooting as the Nikon does. I also note that you can tell a difference between having the noise reduction set to ‘High’ as opposed to ‘Normal’. However, under none of the setting does the camera produce an acceptable result; there is little difference in quality between ISO 400 and ISO 6400; a four stop difference with no real improvement. In other words the added ‘speed’ is negated by the deterioration in image quality even with noise reduction at maximum. Once again it looks like ISO 800 is the maximum viable setting.

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