F Stop Limitations in Canon 7D Autofocus

[Ross_J]

I plan to buy a Canon 7D and a telephoto zoom lens for wildlife photography. One lens I am considering is the Sigma 150-500MM F/5-6.3. Someone told me that the autofocus on Canon cameras will not work on a lens slower than f/5.6. Someone else thought the center autofocus point on the 7D went higher. What are the limitations on the 7D's autofocus? Will autofocus work on a lens slower than f/5.6?

[inkista]

I wouldn't worry about it. I've never seen reports that Sigma f/6.3 lenses stopped autofocusing on Canons at a specific point in the zoom range. The actual AF limit when the body stops attempting to autofocus is when the max. aperture of the lens hits f/8. For most people, practically, this means an f/5.6 lens or faster, which is why that's usually touted as the limit.

Typically what they mean is don't add a teleconverter onto an f/5.6 lens.

[sybren]

If you want to check the specs, the manual is available as PDF file ;-)

[OsmosisStudios]

Originally Posted by inkista

Typically what they mean is don't add a teleconverter onto an f/5.6 lens.

And why most mirror lenses are f/8 and manual focus.

Though I did see a guy with a 2.0TC on a 800mm f/8 mirror. NO idea how the viewfinder was, but presumably DARK.