Early in my photography I was “anti-high ISO.”
First. What is ISO?
In a nut shell, it is the level of sensitivity the senor has to light. By turning up the sensitivity, you allow the camera to shoot at faster shutter speeds in lower light.
There is a down side to turning up the ISO though. The higher it is, the more “noise” you will have in your picture.
The noise is why I was afraid to use ISO in my early days. I was worried that if every picture wasn’t so sharp it cut you to look at it, that no one would like my pictures. As a result, I have ruined a lot of pictures by leaving the ISO down and trying to stabilize slower shutter speeds.
That is not worth it! The amount of noise in a quality picture can often be taken out in post and you get a wonderful photo.
I just shot a graduation at Glen Oaks Community College. The graduation was in the gym. Although the lighting looked great… it was not. I used an ISO of 2000 so I could get a shutter speed of 1/320 and my aperture was set at f/2.8. The pictures turned out very well.
My advice would be to test the limits of your DSLR (as far as ISO goes) and see what is acceptable to you. Don’t be afraid to use it! Get the picture!!!