I just returned from a workshop in Portugal, and we did a lot of street shooting in Porto and Lisbon. We had a lot of fun trying to find the perfect spot for a early morning trolley shot in Lisbon. Yellow trolleys are iconic to Lisbon, so we really wanted to photograph them during our trip. Since we were shooting in predawn light under city lights, our ISO was set to high values…1600, 3200 and even higher. The discussion came up that ISO was all about noise, and not much else. True, noise may be the most obvious side effect. But other image aspects are also affected by high ISO.
Dialing up your ISO amplifies the signal to noise ratio of your sensor. So you amplify both the good and the bad when you increase your ISO. Shadow areas will begin to have speckles, which may not be a bad thing depending on what effect you want. But other things happen as well. Increasing your ISO will decrease your color fidelity and reduce your dynamic range. Your images won’t look as sharp.
What’s the message here? Bottom line, if you need high ISO to get the shot, then use it. I have shot assignments at ISO 3200 and the final images look great in print. ISO performance is amazing in new cameras. But this shouldn’t give you free reign to casually crank up your ISO. I constantly keep track of my ISO, and if I don’t need a high ISO, I will dial down to 400, 200 or 100 if possible. Lower ISO is always better than high ISO when it comes to image quality. If you are making a large inkjet print, you will be better off using the lowest ISO you can use.