Which ISO should you use? What about Auto ISO?
Early digital cameras typically only gave you a choice of 50, 100, 200 and 400 for ISO. Pictures shot at 400 just weren’t very clean and crisp – they had a lot of noise. 50 or 100 gave the best results but weren’t practical in any conditions without LOTS of light. Modern digital cameras offer a choice of ISO from 100 all the way to 6400 or even higher. So which should you most often use? And what about Auto ISO where the camera chooses ISO for you?
You need to have some understanding of the relationship between ISO, shutter speed and aperture (aka f-stop or lens opening). If you need to brush up, read my post Shutter speed, f-stop and ISO.
It would be nice to just shoot everything at 100 ISO since that will give you the “cleanest” image with the least noise (noise is something like graininess in film). I’ve found that 100 ISO though often forces you to use too slow a shutter speed or too large an aperture. If you have a point and shoot camera I suggest you try 200 and also see how well your camera does 400 if light is dim.
With a recent DSLR you have a lot more choices. I typically start at 400 ISO and move up if I’m finding shutter speed too low. I usually shoot in AV or aperture priority mode so I set the aperture/f-stop that I want and check to see what shutter speed the camera chooses. I might go up to 800 ISO even with plenty of daylight if I’m shooting a soccer game or something else where I want pretty high shutter speeds.
Indoors without flash and relatively dim lighting (church, museum, etc.) I try 1600 and if it just won’t work, move to 3200. I rarely use 6400 but if there just isn’t much light at all that’s what I’ll do. I recently was outside around dusk and wanted to capture a picture of my neighbor’s red tree. Even at 6400 with the lens wide open I got a pretty show shutter speed. So I shot at 12,800 ISO. This was the result.
So, if you need to don’t be afraid to bump your ISO as high as it can go to get a shot. Would this have been better on a tripod at ISO 100. Probably but this one is good enough for me.
Here’s another one inside the President’s performance at Disney World that I shot as ISO 12,800 because it was so dark in there.
And here’s one at the Magic Kingdom shot at 6400 ISO
So, if you need to, crank up that ISO. A lot of people are afraid to because of the dreaded noise but that just means that they hand hold at very slow shutter speeds and the resultant picture may not be sharp.
One of the nice things about shooting in AV (aperture priority) mode is that the camera will always give you a shutter speed that works. It may be too slow to handhold so you might need a tripod but it will pick a shutter speed for you. TV or shutter priority mode, on the other hand, has a built in problem. You pick a shutter speed and the camera tries to choose an appropriate lens opening. It may not be able to because the required f-stop is beyond what your camera will support. So you get the dreaded flashing f-stop as the camera tries to tell you this won’t work. You can keep bumping up the ISO a little bit at a time to see if you can get a usable f-stop with the shutter speed you have chosen. This may work fine for you at a soccer game on an overcast day.
But in certain situations you just can’t afford to keep fooling around with camera settings or you’ll miss the shot. If you’re shooting from a moving vehicle you may be going through a whole range of scenes with bright light and dim light. I was recently confronted with just this problem on a train in Switzerland. I wanted to set a high shutter speed so that my pictures from the train wouldn’t be blurry. But the scenes outside were going to be changing rapidly from snow scenes to dark forests and everything in between. If I kept trying to change the ISO to get a usable f-stop I would miss a lot of shots.
The solution was to set the camera to Auto ISO. I set the shutter speed to 1/1000th (in shutter priority mode) and let the camera choose the f-stop. If the camera can’t do the job at a low ISO it will pick a higher one until the combination works.
Here’s the first shot from the moving train 1/1000th sec, f5.6, ISO 100
Here’s one at 1/1000th sec, f4.0, ISO 1600
And finally one at 1/1000th sec, f9, ISO 100
On my camera, a Canon T3i, there is a menu setting for Auto ISO that lets me restrict how high the camera will go. I set this to ISO 1600 but could have set it as high as 6400 if I had expected low light conditions.