Using a cheap ebay extension tube with a 100mm canon macro

[[shingo]]

I guess I will lose autofocus and aperture? So does it mean I'm going to have to put the lens choose the right aperture and then add the extension tube?

I can get those for 10$ I think it's a good price, I'm probably going to use it only a few times.

[LordV]

Yes you would need to preset the aperture on the lens using AV mode and then remove the lens whilst keeping the DOF preview button depressed and then put the ext tubes on. This unfortunately also results in a slightly dim viewfinder.
Brian V.