ISO 100 — or always as low as possible. That’s one of the pieces of advice I learned very early on, and unfortunately followed for far too long.
The pursuit of the lowest possible noise has cost me many good photographs over the years. Because I had to use a slightly wider aperture, and the shallow depth of field ruined the image. Because I had to expose a bit too long, and ended up with slight motion blur.
I’ve moved past this mindset for quite some time now, but I was reminded of it again by this excellent video from Henry Reich’s MinutePhysics.
Take a look — it will likely help you understand ISO better.