Comments on: Canon EF 70-300mm f/4.5-5.6 IS DO USM http://www.elharo.com/blog/photography/2009/10/13/canon-ef-70-300mm-f4-5-5-6-is-do-usm/ Ranting and Raving Sat, 20 Mar 2010 00:22:18 -0500 http://wordpress.org/?v=2.9.1 hourly 1 By: Dolan Halbrook http://www.elharo.com/blog/photography/2009/10/13/canon-ef-70-300mm-f4-5-5-6-is-do-usm/comment-page-1/#comment-847574 Dolan Halbrook Tue, 13 Oct 2009 19:34:49 +0000 http://www.elharo.com/blog/?p=1002734#comment-847574 "From pure physics, sharpness should be maximized at the widest aperture (diffraction increases as the opening narrows) but in practice some lenses have aberrations in the glass such that they actually perform better with a slightly smaller aperture than their maximum." Theoretically, yes, but most if not all lenses perform best stopped down at least one or two stops, as you mentioned. “From pure physics, sharpness should be maximized at the widest aperture (diffraction increases as the opening narrows) but in practice some lenses have aberrations in the glass such that they actually perform better with a slightly smaller aperture than their maximum.”

Theoretically, yes, but most if not all lenses perform best stopped down at least one or two stops, as you mentioned.

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