The Auto ISO mode sets ISO values between 100 and 3200 ISO. Compared to what I am used to (no auto-iso at all on a Canon 10D) this is pretty convenient. Some thoughts so far:
- I noticed that Auto ISO has a strong tendency to go for 100 ISO. That’s nice if there is enough light to get a short shutter speed and a safe amount of depth-of-field. But the camera also used 100 ISO on a 28mm, 1/30 s, f/4 shot in the evening. Arguably this still adheres to the old 1/f-rule for shutter speed. But the quality (noise, dynamic range) difference between 100 ISO and 200 ISO is minimal (although visible in DxOmark ‘s measurements). I thus wonder how often that stop could be put to better use like having a 2x faster shutter speed or getting more depth of field.
Update (16-Mar-09): a work-around to increase the minimum ISO from 100 to 200, is to enable “Highlight Tone Priority”. This, as a side-effect, sets the minimum ISO value to 200.
- Maybe this is overoptimistic, but are the “only” conditions when one would overrule Auto ISO might be for either landscapes using tripods (where 100 ISO is a good idea) or sports photography (where increased ISO is a good idea).
See manual page 58.