How good is "good enough" in AF micro adjustment? 24-105 L F4 & EOS 6D MkII

[Skip70]

I'm calibrating my lenses (for the first time) on my 6D MII and am encountering an issue that I did not expect.

The 24-105 L F4 keeps showing a near or close focus point, even when I have the calibration dialed out to +15. Yes, I know I could go to +20 but I was surprised it would take that much. Can a lens be that far off?  

[rs-eos]

Did you check focus points with various focal lengths and distances?  I think this gets tricky with zoom lenses as you may have to average out the adjustments.

The only time I have ever had to apply micro adjustments so far was with my EOS 6D (1st gen) when using my EF 50mm f/1.2L.  This same exact lens needed no adjustments with my current EOS 5D IV.

[Skip70]

Thank you for the on-point reply. Yes, I do know where is a bit of averaging to do on a zoom, but it is consistently close focusing across all focal lengths. (By the way, you need to loan me that 1.2 to verify my results and then forget that you sent it to me! Nice glass.)

[deebatman316]

First you're calibrating the camera body's AF system to a lens. The lens doesn't know if its in focus or not that's the camera's AF system's job. But every lens will require a different amount of adjustment. Usually L lenses don't need or will need very little adjustment. Personally I would have Canon make AFMA adjustments.

[wq9nsc]

I don't own the 24-105 but my 70-200 f2.8 and 200-400 f4 have separate micro-focus calibrations for the wide and tele settings.

I have never seen anything needing more than 4 points of correction and most of my L series are dead on without calibration to multiple 1DX II and III bodies.  +15 is VERY unusual.

Rodger

[Waddizzle]

Performing AFMA is just as much a test of the photographer as it is the gear.  What instructions are you following?  I believe the “Dot-Tune Method” is fairly quick and accurate.

https://youtu.be/7zE50jCUPhM?si=xMDsHybhlE32NDtW 

Pay attention to your distances to your test subject.  Use 25-50x the focal length, which needs to be adjusted for any crop factor.  Calibrating under artificial lighting can produce different results compared to calibrating in outdoor sunlight.

My one fault with the Dot-Tune video is that they do not encourage you to take multiple test shots of your focus target, and then average the result.  Focus.  Take a test shot.  Defocus the lens.  Repeat several times.  If your test results are all over the map, then your technique is weak and flawed.  

The devil is in the details.  Almost no one gets it right the first time.  Do it once.  Recheck a week later.

[ebiggs1]

"... my L series are dead on without calibration to multiple 1DX II and III bodies.  +15 is VERY unusual."

Most lenses especially L level do not require it on 1 Series, xD or xxD series. None of my several L lenses have needed it or benefited from it. If +15 is a fact I would send that lens/camera to Canon and ask them to service it.

The biggest reason that people seem to think a lens is not focusing correctly is because of the user error and not the lens or camera. Another point that is often overlooked is with focus adjustment you are simply moving the critical focus point forward or backward from where the default setting that Canon originally set. Another misconception is people think, is focus adjustment makes a lens sharper, it does not.

The oddity here is the cameras and lens combos like a Rebel series with kit lens which are more in need of focus calibration do not have that ability

[Waddizzle]

“ The oddity here is the cameras and lens combos like a Rebel series with kit lens which are more in need of focus calibration do not have that ability “

There is nothing “odd” about it.  Most consumer lenses have AF motors with too much backlash.  The results are not very repeatable because the AF motors will cause focus to undershoot or overshoot the mark.  

The camera gives a STOP command, but the lens motor does not stop on a dime.  This is the problem with some non-L EF primes that have a reputation for not being sharp wide open, when the DOF is at its narrowest.  

[Skip70 · Accepted solution]

I appreciate many of he responses. I learned a lot, always do from the folks here. 

I tried all three "systems" - the tent card, shooting at an angle to a lined target on a table top, and Dot-Tune. I liked the latter the most because of the challenge it presented to be so methodical and exacting. 

Net out: Hah, all of my Canon lenses (all Ls) were just about spot-on with an average within a point or two of zero. All three methods, when properly and carful executed, came to essentially the same result. 

Now, back to my job in getting great focus!

[Waddizzle]

Congratulations, I think.  It sounds like you have it figured out.  As I indicated above, performing an AFMA is a much a test of the photographer as it is the gear.  You just have to take you time and be meticulous at every step along the way.