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ISO - What's Best When?

I was asked the other day by a pretty decent amateur photographer no less… What ISO should I use at any given time? This caught me a little off guard and my instant reaction was to tell her she should be using the lowest one she can get away with. She was polite about the whole thing but upon further reflection thats probably not what she was asking and anyone who is even half-way decent already knows to keep their ISO as low as possible.

I’m just going to quickly re-cap for anyone who’s picking up a camera for the first time. ISO is sensitivity and raising the speed is a compromise measure that we only take when we have to in order to get extra shutter speed or to use a narrower aperture since on its own a higher iso always has deleterious effects. The higher the ISO is raised the worse these effects get smearing colors, creating noise, destroying sharpness, killing contrast, etc… The effects are never good so the trick comes from understanding where and when it’s ok to compromise.

The first question you’ll need to ask yourself is; What exactly am I shooting and how is it going to be used? Here are a couple examples.

  1. Lets say you’re out photographing a beautiful night time vista that you plan to later print out and show off or perhaps even sell. If you were to crank up your ISO high it would introduce a number of photographic flaws including heavy noise and massively reduced sharpness. The solution here would be to use a tripod or some other support to allow for a multi-second exposure. Given it’s intended use I probably wouldn’t even bother taking the picture if I couldn’t do it right.
  2. It’s night time and you’re out at a party with your camera. You’re planning on using these photos on Facebook, sending them out to a news agency or maybe you’ll make some 4×6 photos. This is the kind of place where capturing the moment is more important than every minute detail. Even if you could get everyone to wait around for you to set up with a tripod you’d still need a decent shutter speed to make sure they’re sharp. You’ve really got two options here you can crank your ISO up nice and high and deal with the noise or you can start using your flash as the main light source in the room. I personally prefer to use flash as a fill light in these situations and I just deal with the noise but this is a matter of artistic preference.

Once you’ve gotten a handle on what your subject is going to be and if noise is going to be acceptable or not you’ll need to figure out what your camera does at each ISO setting and if you can live with it for a given subject. For my uses with my 1Dx I like to keep my ISO at 100 if I’m photographing for a gallery print. I’ll go up to 400 if I really have to and I can’t figure out a good way around it but after that I’ll just pack up and leave because the resulting photograph would be substandard. At an event I’ll go as high as 6400 before I feel the photograph is really starting to suffer. I keep 12,800 in reserve as emergency war speed but even though my camera will go to 204,800 I won’t go past 12,800 with my 1Dx for any reason. Every camera, photographer, and situation is different so it’s important that you go out with your camera and figure out what your limits are for any given situation.