It really depends on a lot of things as to how often I change ISO

1: What do I want out of the photo, motion blurr, no blurr
2: What conditions do I have light wise
3: what is my main subject
4: what does the customer want

In no particular order. Normally when shooting for the AP at Indy they require minimum 800 ISO and 1000 shutter with all control by the aperature for proper expsoure.

JS