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+--- Thread: Sigma 105mm f/2.8 Macro DG OS HSM:optimum aperture (/showthread.php?tid=530)
Sigma 105mm f/2.8 Macro DG OS HSM:optimum aperture - JJ_SO - 06-22-2017
Actually, Nikon DSLRs show the effective f-stop of "micro" lenses (even the plasticky 40/2.8), not only the max. available. Good thing for manual flashes, I think. This effect can be watched when focus at infinity, leave the aperture, then focuse at much closer - aperture number goes up. I'm not sure, if it's a full f-stop, but it is significant.