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Archive 2012 · Canon 85mm 1.2L II - AF Inconsistency
  
 
thetaobear
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p.1 #1 · Canon 85mm 1.2L II - AF Inconsistency


I was wondering if anyone has the problem.

When I shoot subjects that are closer to me (10 feet or less), I realized MA +11 works the best. So I tuned it that way. However, when I shoot a subject that is greater than 10 feet- MA +11 will cause back-focus. At MA 0, the focus is perfect. Is this common? This is quite annoying that I have to change my AF MA at different scenarios.

My problem is that the MA difference is pretty significant, which causes the subject to be really out of focus when the MA is not set correctly.

Any fixes possible?

Thanks!


Feb 08, 2012 at 10:06 PM
Binh Ly
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p.1 #2 · Canon 85mm 1.2L II - AF Inconsistency


The 85L is one of the most accurate focusing lenses I have ever used. It is slow but once it acquires it is very accurate. I've never experienced your problem so you might want to send it in to Canon.


Feb 08, 2012 at 10:19 PM
panm
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p.1 #3 · Canon 85mm 1.2L II - AF Inconsistency


My 85LII is also one of my most consistent AF lenses at any distance.

Funny thing is that I am experiencing a similar problem with what you describe with my 50mm sigma.

http://www.fredmiranda.com/forum/topic/1084009

P.


Feb 08, 2012 at 10:40 PM
mttran
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p.1 #4 · Canon 85mm 1.2L II - AF Inconsistency


thetaobear wrote:
I was wondering if anyone has the problem.

When I shoot subjects that are closer to me (10 feet or less), I realized MA +11 works the best. So I tuned it that way. However, when I shoot a subject that is greater than 10 feet- MA +11 will cause back-focus. At MA 0, the focus is perfect. Is this common? This is quite annoying that I have to change my AF MA at different scenarios.

My problem is that the MA difference is pretty significant, which causes the subject to be really out of focus when the MA is not set correctly.

Any fixes possible?

Thanks!

Your final focal plan is (1/3 DOF +/-1/8*MA_Index*DOF) but your MA_Index is always a constant number regardless to active DOF (function of : aperture, subject distance, etc...).

MAF system does not work well if MA_Index is larger than (+/-) 5. Send camera and lens in for zero MA_Index calibration


Feb 08, 2012 at 10:52 PM
AJSJones
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p.1 #5 · Canon 85mm 1.2L II - AF Inconsistency


mttran wrote:
Your final focal plan is (1/3 DOF +/-1/8*MA_Index*DOF) but your MA_Index is always a constant number regardless to active DOF (function of : aperture, subject distance, etc...).

MAF system does not work well if MA_Index is larger than (+/-) 5. Send camera and lens in for zero MA_Index calibration

Could you elaborate on this - I'm confused by what you are explaining.
Thanks


Feb 08, 2012 at 10:56 PM
mttran
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p.1 #6 · Canon 85mm 1.2L II - AF Inconsistency


AJSJones wrote:
mttran wrote:
Your final focal plan is (1/3 DOF +/-1/8*MA_Index*DOF) but your MA_Index is always a constant number regardless to active DOF (function of : aperture, subject distance, etc...).

MAF system does not work well if MA_Index is larger than (+/-) 5. Send camera and lens in for zero MA_Index calibration

Could you elaborate on this - I'm confused by what you are explaining.
Thanks

Canon MAF requirement:

1) Focal plan will be within 1/3 DOF
2) Each unit of MA_Index = 1/8 DOF

Your desire MA_Index was set by you with certain DOF (constant len aperture and constant subject distance) and this MA_Index will be used by camera F/W to (+/-) offset the lens movement while focussing.

Final Focal Plan to be at ~ 1/3 DOF (+/-) MA_Index (1/8 DOF)

In realife, your subject DOF is changing but your MA_Index value is not since your last MA test set up.

Please, note MA_Index is a function of DOF and it should be re-calculated in realtime as well.

Hope this helps
Feb 08, 2012 at 11:22 PM
mttran
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p.1 #7 · Canon 85mm 1.2L II - AF Inconsistency


Binh Ly wrote:
The 85L is one of the most accurate focusing lenses I have ever used. It is slow but once it acquires it is very accurate. I've never experienced your problem so you might want to send it in to Canon.

+1


Feb 08, 2012 at 11:53 PM
Copypaste
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p.1 #8 · Canon 85mm 1.2L II - AF Inconsistency


Mine is overall excellent. No problems I'd have it checked out.


Feb 08, 2012 at 11:55 PM
 



AJSJones
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p.1 #9 · Canon 85mm 1.2L II - AF Inconsistency


mttran wrote:
AJSJones wrote:
mttran wrote:
Your final focal plan is (1/3 DOF +/-1/8*MA_Index*DOF) but your MA_Index is always a constant number regardless to active DOF (function of : aperture, subject distance, etc...).

MAF system does not work well if MA_Index is larger than (+/-) 5. Send camera and lens in for zero MA_Index calibration

Could you elaborate on this - I'm confused by what you are explaining.
Thanks

Canon MAF requirement:

1) Focal plan will be within 1/3 DOF
2) Each unit of MA_Index = 1/8 DOF

Your desire MA_Index was set by you with certain DOF (constant len aperture and constant subject distance) and this MA_Index will be used by camera F/W to (+/-) offset the lens movement while focussing.

Final Focal Plan to be at ~ 1/3 DOF (+/-) MA_Index (1/8 DOF)

In realife, your subject DOF is changing but your MA_Index value is not since your last MA test set up.

Please, note MA_Index is a function of DOF and it should be re-calculated in realtime as well.

Hope this helps

Thanks - although I'm still a little confused, but less so

This information on the MFA index etc must come from some Canon white paper or discussion somewhere. Could you find a link for me? I'd like to make sure I have all the info I can.


Feb 08, 2012 at 11:56 PM
mttran
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p.1 #10 · Canon 85mm 1.2L II - AF Inconsistency


AJSJones wrote:
This information on the MFA index etc must come from some Canon white paper or discussion somewhere. Could you find a link for me? I'd like to make sure I have all the info I can.

This might be a tough one Yeah, i have read this somewhere but can't remember. I will try to find them.


Feb 09, 2012 at 12:25 AM
rantonishak
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p.1 #11 · Canon 85mm 1.2L II - AF Inconsistency


thetaobear wrote:
I was wondering if anyone has the problem.

When I shoot subjects that are closer to me (10 feet or less), I realized MA +11 works the best. So I tuned it that way. However, when I shoot a subject that is greater than 10 feet- MA +11 will cause back-focus. At MA 0, the focus is perfect. Is this common? This is quite annoying that I have to change my AF MA at different scenarios.

My problem is that the MA difference is pretty significant, which causes the subject to be really out of focus when the MA is not set correctly.

Any fixes possible?

Thanks!


Just curious.... What camera body are you using when this problem occurs ?

Do you have the option of using a different camera body with the lens to test ?

Please let us know...
Feb 09, 2012 at 12:30 AM
twistedlim
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p.1 #12 · Canon 85mm 1.2L II - AF Inconsistency


Mine is snap on wide open. I am amazed at how accurate the focus is. More accurate than any lens I have owned. I would stop messing with the micro adjustment and send it in for calibration. This lens should need no adjustment.


Feb 09, 2012 at 02:39 AM
thetaobear
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p.1 #13 · Canon 85mm 1.2L II - AF Inconsistency


Thanks everybody for the inputs! I am using it with the 5D Mark II. I shot a wedding with the 1D Mark IV and had the same problem.

It is very strange because before it did not have this problem- the lens has never been dropped or damaged! I think I'll be sending it to Canon. The AF is just strange.

I really hate messing with the MFA with my lenses- because the more I use it the more frustration it gets especially when I start MFA quite a bit (e.g. +5 or above).


Feb 09, 2012 at 07:21 AM
thetaobear
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p.1 #14 · Canon 85mm 1.2L II - AF Inconsistency


Does anybody know how much calibration will cost (CPS gold)? This is out of warranty. Does the cleaning/check-up coupon cover it?


Feb 09, 2012 at 07:22 AM
twistedlim
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p.1 #15 · Canon 85mm 1.2L II - AF Inconsistency


$285 for those of us not CPS gold. Apply your discount from there.


Feb 09, 2012 at 12:28 PM
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