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5d mark III front focus problem

mo
Apprentice

my 5d mark III has a problem with front focus. I use only crosstype focus points but even cental one can't focus correctly no matter what lens I use. the problem is more significant further the subjet focused on is. tried different light conditions with the same result. Camera always front focusing significantly, so the suject is out of DOF all the time. tested lenses 50/1.4 and 24-70/2.8 L. problem persist in all AI modes (focus/servo). please could you provide any solution? thanks in advance

18 REPLIES 18

TCampbell
Elite
Elite

See:  http://www.lensrentals.com/blog/2008/12/this-lens-is-soft-and-other-myths

 

Your 5D III will let you adjust some thing called "Autofocus Micro-adjustment" (AFMA).  You can either do this gloally (for all lenses) or you can do it on a per-lens basis.

 

Although... if EVERY lens needs it... and needs a LOT of it... I think you might prefer to send the camera to Canon for correction.

 

Tim Campbell
5D III, 5D IV, 60Da

thanks, I think that the problem is beyond AFMA capabilities, hope sending it back to Canon will solve this.

Also... before you go through the bother to send this to Canon, make sure you've carefully tested it.  

 

That means:

 

1)  Camera on tripod (never hand-hold a camera for a focus test because if you sway or lean after it locks focus then you just invalidated the test.)

 

2)  Pick a single AF point and make sure it's on your target.  Don't let it use just any AF point.  It'll gravitate to the AF point that can lock focus at the nearest focus distance (which could be mistaken for front-focus even though it's working exactly as intended).

 

3)  Use a real focus test target - not a typical subject.  You can use a commercial focus chart, or you can download one from the internet, print it out, follow the instructions, and do the test that way.  Here's one I like:  http://regex.info/blog/photo-tech/focus-chart

 

When testing, I like to run the focus all the way in (closest focus distance) so that the camera is forced to move the focus on the lens.  Repeat a half dozen times and take notes of which shots started with focus all the way "in".  THEN... manually run the focus all the way out (to infinity) and repeat that test a half-dozen times, while taking careful note of which frames were tested with the focus starting at infinity.

 

Import the images to your computer and analyze:  

(a) is it missing focus ALWAYS or just sometimes?

(b) does it always miss focus in the same direction (e.g. always front focus?  or random?)

(c) does it miss focus the same regardless of whether you started with focus "in" vs. with focus "out"?  If focus misses different in one direction than in the other it could indicate some mechanical gear backlash (loose gears) in your lens.

 

Tim Campbell
5D III, 5D IV, 60Da

If you do decide to do MFA, make sure you are not real close to 'close focus' of the lens.  Usually, 50 times the focal length of the lens is the rule.

EB
EOS 1DX and 1D Mk IV and less lenses then before!


@ebiggs1 wrote:

If you do decide to do MFA, make sure you are not real close to 'close focus' of the lens.  Usually, 50 times the focal length of the lens is the rule.


I'm not 100% sure what you're driving at; but it may be worth pointing out that the 5D3 allows two AFMA settings per lens, one at each end of the lens's range.

Bob
Philadelphia, Pennsylvania USA

Does it, Bob?

The 1Dx allows 2 settings but only on a zoom lens, at each end of the zoom range.

 

George.


@KingEyre wrote:

Does it, Bob?

The 1Dx allows 2 settings but only on a zoom lens, at each end of the zoom range.

 

George.


Yes, that's what I meant. I don't know for a fact that the 5D3 doesn't let you set two values for a prime (I don't have any FF-compatible primes to test it with), but I'd have to assume that it works the same way as the 1DX.

Bob
Philadelphia, Pennsylvania USA

Yes, I'm almost certain it's the same as the 1 Dx, ie a setting for each end of a zoom....and that's also available in the 7D2.

 

George.


@KingEyre wrote:

Yes, I'm almost certain it's the same as the 1 Dx, ie a setting for each end of a zoom....and that's also available in the 7D2.

 

George.


Then that's another added feature of the 7D2. The 7D has only one setting per lens.

Bob
Philadelphia, Pennsylvania USA
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