Sigma 150mm F2.8 Macro dumb question
Excuse me if the question is too basic, I am just getting started with Macros.
I recently bought a Sigma 150mm f2.8 Macro. However, I found that I get f2.8 only when the distance scale on the lens is set to infinity. At all other distances, I get less than f2.8 (at least with the limited testing).
Can someone clarify what's the deal here?