macro lens aperture
I have the bug for a 100 mm macro lens. The Canon lens looks like a fine choice however for a few bucks less I could pick up a Tamron, Tokina, or Sigma. I have noticed that the third-party lens elements extend when focusing. the Canon lens has an internal focusing which on one hand seems like an advantage. What I'm wondering is when the element extends on the third-party lenses does that change the effective aperture setting? Or does he aperture remain constant no matter what the focusing distance. I'm wondering which lens will allow me to stop down the furthest so that I can have the best depth of field. Thanks,
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