Higher ISO speeds will give you grain or on digital it is called noise but this is not necessarily a downside, it can compliment a photograph depending on what you are trying to achieve. For example grainy B&W photos are still favored for certain styles.

If holding the camera, I don't let the shutter speed fall below 30 as I know my limits.

Say for example, my aperture was set to 2.8mm which let in the most light for the lens I had on the camera at the time, my ISO was set to 100 but using the cameras meter it told me it would be underexposed and my shutter speed was already at 30 so I know I'd get camera shake if I lowered the shutter speed any further. To overcome this, I'd increase to ISO to 400, 800 and maybe much higher depending on the lighting conditions and if I was somewhere that wouldn't allow me to use flash.

If you were doing long exposures on a tripod then you can set you ISO to it's lowest setting make an exposure at f22 for 20 secs for example and a typical scenario for this would be a night shot. Using a high ISO setting in the dark, you'll really notice the noise in the dark areas and other areas close up.

Don't be afraid to use the higher ISO settings as you might loose an otherwise great shot due to camera shake! Practice and practice with different combinations of ISO, shutter speed and aperture and become confident with them.

There are always noise reduction techniques you can use in your post processing workflow to fix the noise.

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Paul

www.phrphotography.com