October 01, 2014, 05:02:35 AM

Author Topic: Can someone explain the Canon 50mmL f/1.2 "backfocus problem" ?  (Read 12898 times)

kaihp

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Re: Can someone explain the Canon 50mmL f/1.2 "backfocus problem" ?
« Reply #30 on: May 17, 2013, 09:14:36 AM »
http://toothwalker.org/optics/spherical.html

Thanks for the link, neuro, that explained it so even I could understand it  :)

This might also explain why I see my 70-200IS MkI needs different AFMA at 200mm MFD than at "reasonable" distance. IIRC, there were 6 AFMA points between the best MFD setting and the "normal" setting.

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Re: Can someone explain the Canon 50mmL f/1.2 "backfocus problem" ?
« Reply #30 on: May 17, 2013, 09:14:36 AM »

Pi

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Re: Can someone explain the Canon 50mmL f/1.2 "backfocus problem" ?
« Reply #31 on: May 17, 2013, 11:07:05 PM »
The focus shift can only be a problem if you focus too close. I have used two copies of he 50L, and I have never noticed any focus shift problems.

Yes, the problem is more evident at or close to the MFD.  But just because that's "too close" for you, doesn't mean that's true for everyone who uses the lens.   One could also say, it's only a problem if you shoot too stopped down - Someone who always shoots wide open would also "never notice a problem."

You read too much into my remark.

Pi

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Re: Can someone explain the Canon 50mmL f/1.2 "backfocus problem" ?
« Reply #32 on: May 17, 2013, 11:13:15 PM »
I've seen the phrase "as long as you aren't too close" a few times (or variations of it), and neuro mentioned it is most evident at/near MFD.

Which for me kind of begs the question: at what distance to subject would the problem become less of an issue (or a total non issue)? Asking, because I frequently have to change from wide open to about f/4~5.6 with subjects about six feet away (3 or more times MFD). I shoot full frame, if that matters.

In my experience, 6 ft is fine. I can focus with my 5D2 with the outer AF points (!) in AI servo, no problems.

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Re: Can someone explain the Canon 50mmL f/1.2 "backfocus problem" ?
« Reply #32 on: May 17, 2013, 11:13:15 PM »