Should I keep Image Stabilization (IS) off when I do not actually need it?

Question

I own a Canon 7D and a EF-S 15-85 IS lens and I keep the image stabilization turned on all the time.

Recently, an experienced photographer told me that this is a huge mistake because it reduces image quality overall.

Except the battery draining, is there any evidence that using IS the image quality will be reduced?

Thank you :)

Answer

I don't know how it works with this lens, but I've seen charts for Pentax's in-body stabilization system where the data shows that contrary to conventional wisdom I.S. gives a (decreasing but still there) benefit up until rather high shutter speeds, at which point it doesn't matter (and doesn't make things worse).

If you have the camera on a very steady tripod, though, off is probably better. On a lightweight, wobbly tripod, it may be different.

It's also important to keep in mind that the stabilization takes time to engage and "settle" — typically half a second or so after you half-press the shutter button. If you have it on, make sure to allow that time.

Update: I don't think these are the charts I remember, but they show the same thing and are quite well done: How can I determine the minimum shutter speed to avoid blur from camera shake?.

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