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Message: <blockquote data-quote="tjsimonsen" data-source="post: 1424305" data-attributes="member: 38764">I don't think the focal length of the Canon varies, but the aperture does! Whether or not that is a problem I don't know (I have the old non-USM 100/2.8 Canon which does extend while focussing).I wouldn't care much about the AF speed of a macro. When you are working in the macro-zone you set the lens to a certain magnification and focus by moving the camera.The bottom line here is that the differences between the various 100mm macros are not in the optics - they are all stellar.Thomas</blockquote>