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.
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.
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.
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
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
AJSJones wrote:
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.
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) 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 ...Show more →
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.
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.
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.
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.
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).
I'd have it checked out.