Sigma 150mm F2.8 Macro dumb question

Started May 4, 2010 | Discussions thread
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abhijitsarkar
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Sigma 150mm F2.8 Macro dumb question
May 4, 2010

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?
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Abhi

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