arthur_zwiegincew

I did this comparison fairly recently. I found the results very interesting: the 1.4 is better in most aspects, especially at f/1.8, in dark conditions, focused fairly closely (I tested at 2 m), but it has a pretty big flaw — it exhibits visible purple veiling wide open in bright light. See the attached image (50/1.8 Mk II on top, 50/1.4 below). Both shots were at f/1.8, 1/5000 s off a tripod with MLU. I actually tested two different 1.4 lenses, and they both came out very similar.<br/><br/>Of course, this really isn't a big deal, because how often do you shoot (nearly) wide open in bright daylight?<div></div>

<i>> It's obvious to me that, while Canon specifies f/5.6 as the minimum aperture for all these AF systems to work, some handle f/8 or beyond better than others.</i>

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I never understood why they specify the AF limit in terms of aperture. Wouldn't that depend only on the amount of light? E.g. wouldn't it be easier to focus at f/16 at noon on a sunny day than at f/5.6 in the evening? Is increased DOF at lower apertures the culprit?