April 25, 2017, 05:05:58 AM

Author Topic: Can someone explain the Canon 50mmL f/1.2 "backfocus problem" ?  (Read 31552 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.

Deltrus

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Re: Can someone explain the Canon 50mmL f/1.2 "backfocus problem" ?
« Reply #33 on: January 08, 2017, 06:24:19 PM »
Hi there, I am unable to create my own threads yet, probably due to a lack of posts, but my topic would have echo'd this thread's very closely...

I just got the 50mm f/1.2 L yesterday and I am having some severe back-focusing issues. I've confirmed with multiple shots at the wide open aperture of f/1.2 of a ruler. In each shot, the number and lines behind the one I tried focusing on with spot AF were sharper and had better contrast. I'd really like to keep this lens and use it, but I am worried about such a glaring problem, so many people here are saying it should only happen at narrower apertures, but it's happening, and blatantly so, at 1.2 for me. Help!

Hector1970

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Re: Can someone explain the Canon 50mmL f/1.2 "backfocus problem" ?
« Reply #34 on: January 08, 2017, 07:26:30 PM »
I love my 50 1.2. I don't find the focus shift an issue in reality.
The shallow depth of field is more of an issue but even at that my copy focusses really well.
To The last poster, if the lens is new send it back if you are not happy with it. Make sure you are doing your test with a tripod.
« Last Edit: January 09, 2017, 08:50:08 AM by Hector1970 »

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Re: Can someone explain the Canon 50mmL f/1.2 "backfocus problem" ?
« Reply #35 on: January 09, 2017, 07:38:20 AM »
Hi there, I am unable to create my own threads yet, probably due to a lack of posts, but my topic would have echo'd this thread's very closely...

I just got the 50mm f/1.2 L yesterday and I am having some severe back-focusing issues. I've confirmed with multiple shots at the wide open aperture of f/1.2 of a ruler. In each shot, the number and lines behind the one I tried focusing on with spot AF were sharper and had better contrast. I'd really like to keep this lens and use it, but I am worried about such a glaring problem, so many people here are saying it should only happen at narrower apertures, but it's happening, and blatantly so, at 1.2 for me. Help!

AFMA.  It should be set to hit the target accurately wide open using the center point.  Some camera bodies don't have AFMA, at which point the lens and body should be sent in to be recalibrated.

cayenne

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Re: Can someone explain the Canon 50mmL f/1.2 "backfocus problem" ?
« Reply #36 on: January 09, 2017, 10:04:20 AM »
Hi there, I am unable to create my own threads yet, probably due to a lack of posts, but my topic would have echo'd this thread's very closely...

I just got the 50mm f/1.2 L yesterday and I am having some severe back-focusing issues. I've confirmed with multiple shots at the wide open aperture of f/1.2 of a ruler. In each shot, the number and lines behind the one I tried focusing on with spot AF were sharper and had better contrast. I'd really like to keep this lens and use it, but I am worried about such a glaring problem, so many people here are saying it should only happen at narrower apertures, but it's happening, and blatantly so, at 1.2 for me. Help!

AFMA.  It should be set to hit the target accurately wide open using the center point.  Some camera bodies don't have AFMA, at which point the lens and body should be sent in to be recalibrated.

Where and to whom at Canon do you send your camera and lenses in to be calibrated?
How much does it cost and how long does it take?

TIA,

cayenne

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Re: Can someone explain the Canon 50mmL f/1.2 "backfocus problem" ?
« Reply #36 on: January 09, 2017, 10:04:20 AM »

Sharlin

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Re: Can someone explain the Canon 50mmL f/1.2 "backfocus problem" ?
« Reply #37 on: January 09, 2017, 10:14:47 AM »

Where and to whom at Canon do you send your camera and lenses in to be calibrated?
How much does it cost and how long does it take?


Depends on your country. Not necessarily to "Canon" per se but to a local licensed service shop.

neuroanatomist

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Re: Can someone explain the Canon 50mmL f/1.2 "backfocus problem" ?
« Reply #38 on: January 09, 2017, 10:40:39 AM »
Hi there, I am unable to create my own threads yet, probably due to a lack of posts, but my topic would have echo'd this thread's very closely...

I just got the 50mm f/1.2 L yesterday and I am having some severe back-focusing issues. I've confirmed with multiple shots at the wide open aperture of f/1.2 of a ruler. In each shot, the number and lines behind the one I tried focusing on with spot AF were sharper and had better contrast. I'd really like to keep this lens and use it, but I am worried about such a glaring problem, so many people here are saying it should only happen at narrower apertures, but it's happening, and blatantly so, at 1.2 for me. Help!

AFMA.  It should be set to hit the target accurately wide open using the center point.  Some camera bodies don't have AFMA, at which point the lens and body should be sent in to be recalibrated.

+1

If backfocus is seen wide open, AFMA is the answer.
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Re: Can someone explain the Canon 50mmL f/1.2 "backfocus problem" ?
« Reply #39 on: January 09, 2017, 11:27:55 AM »
Hi there, I am unable to create my own threads yet, probably due to a lack of posts, but my topic would have echo'd this thread's very closely...

I just got the 50mm f/1.2 L yesterday and I am having some severe back-focusing issues. I've confirmed with multiple shots at the wide open aperture of f/1.2 of a ruler. In each shot, the number and lines behind the one I tried focusing on with spot AF were sharper and had better contrast. I'd really like to keep this lens and use it, but I am worried about such a glaring problem, so many people here are saying it should only happen at narrower apertures, but it's happening, and blatantly so, at 1.2 for me. Help!

AFMA.  It should be set to hit the target accurately wide open using the center point.  Some camera bodies don't have AFMA, at which point the lens and body should be sent in to be recalibrated.

Where and to whom at Canon do you send your camera and lenses in to be calibrated?
How much does it cost and how long does it take?

TIA,

cayenne

Canon.  I've never done it personally, although I came close.  I had a 24L II that wasn't focusing right, and they fixed it (under warranty).  If that didn't work, then I would have had to send in the body as well.  I'm guessing that the cost would be a couple hundred USD or more, which is one reason why I avoid bodies that don't have AFMA.  It also explained why my 20D + 17-55 f/2.8 IS never was quite right.  There was no AFMA on the 20D, so I took more shots to compensate for it.  Then I tried a friend's 7D with AFMA dialed in, and I suddenly, the 17-55 shots looked a lot better.

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Re: Can someone explain the Canon 50mmL f/1.2 "backfocus problem" ?
« Reply #39 on: January 09, 2017, 11:27:55 AM »