AF Micro Adjust

[bob williams]

I know, This subject has been beat to death here on the forums, but.........Just a reminder to all, Don

[Richard Lane]

I have to do this too!


All of my lenses are on "0" no AFMA.


I wonder if I will get sharper shots?


I got a Lens Align Pro for X-Mas and I haven

[Jayson]

Bob, i would say if they are that off, you should send them into Canon service. I think by their standards, the lenses are only off around the +3 -3 range. All of my lenses either are right on or 1 or 2 either way, nothing more than that. My 50mm 1.4 was off way more than that, but Canon service fixed that pretty quickly. just a suggestion.

[HDNitehawk]

I wonder if I will get sharper shots?

Rich if they don't go back to setting them at "0" [:P]

[Pieter]

I second Jayson

[HDNitehawk]

I second Jayson's suggestion. You may/should expect more from a $7000 lens...

Provided it is the lens and not the camera. With my 5D II and 1D IV my 500mm is dead on with no adjustment, with my 7D it is off and had to be adjusted.

[Pieter]

Ah, yes, that

[tkerr]

Bob, i would say if they are that off, you should send them into Canon service. I think by their standards, the lenses are only off around the +3 -3 range. All of my lenses either are right on or 1 or 2 either way, nothing more than that. My 50mm 1.4 was off way more than that, but Canon service fixed that pretty quickly. just a suggestion.

I agree that it should have to be that much of an adjustment. However, the amount of micro adjustment needed for a lens isn't dependent on the lens only. What if his camera is off more than the lens?


For those who might not have read this article already.
http://www.canonrumors.com/tech-articles/this-lens-is-soft-and-other-myths/

[neuroanatomist]

I wonder if I will get sharper shots?

I'd have to say definitely maybe. [:P]


If you are shooting at narrower apertures, since the deeper DoFs mask a slight misfocus, you may not see a difference. The +5 adjustment on my 85mm f/1.2<span style="color: #ff0000;"]L II makes a substantial difference. The -1 adjustment on my 35mm f/1.4<span style="color: #ff0000;"]L, given that it's a wide angle lens, probably makes very little difference.


Also, as Rick has commented, AF is not perfect. For any shot, there is an 'ideal' or 'correct' focal plane.


The first hurdle is that what you think is correct is also what the camera 'thinks' is correct - remember that the actual AF point is larger than it's little representative box in the viewfinder, so if you've got your chosen element right under the box but there's a high-contrast feature at a different distancejust outside that little box, the AF system will likely lock onto the latter.


Assuming the camera is trying to lock onto the correct feature, it's then an issue of the AF system's precision and accuracy. I posted this diagram previously:





Each little black dot would represent one autofocus attempt (i.e. one shot). Obviously, what you want is case 'A' - precise and accurate. AF microadjustment corrects the accuracy - i.e. calibrates the camera/lens combination so that the focal plane the camera is trying to hit is actually the correct one. So, with a proper calibration, you have an accurate system, meaning you get either 'A' or 'B', because the average is close to 'true'.


The other thing to remember is that not every shot will be perfect. The actual focal plane after AF will be a normal (Gaussian) distribution around where the AF system was 'aiming'. So, any single shot may be off - and whether it's off by enough of a margin to notice will depend on the subject. Precision matters here. Assuming you have a correctly calibrated (microadjusted) lens+body combination, the system should be accurate, so we can represent the diagram above a little differently:





The center of the peaks ('0' on the x axis) is the 'true' focal plane. The lines are the distribution of actual focal planes over many, many shots. The blue line represents the results from the regular f/5.6-sensitive sensors, and the red line represents the results from the high-precision f/2.8-sensitive center point (or f/4 on a 1-series body).

[bob williams]

John, Great explanation. I have a job opening for a prison school teacher; are you interested[:#]. Anyway, after shooting yesterday, I am not so sure it was my AF perhaps my technique is more to blame. Let me explain.


I haven't coughed up the money for a lens align system, so I was using my own homemade contraption with some info and printsI got off the internet; And even though it did show that I was back focusing, I have to admit that the entire setup was less than "scientifically accurate". Anyway, I went out and shot some little birds yesterday and what do you know, I am still less than impressed. After carefully analyzing the shots, it seemed that the sharpness is in the middle of the little bird and not so much the head and eye. So, now I am seriously questioning my technique and not so much the calibration of the equipment. Anyway,I am going to try the settings with and without adjustments, but concentrate on focusing on the eye. Also, I ran the dof calculater for a 7d and a 500 @ f4 @ 20 ft and the DOF is only .07 ft or o little over 1/2 inch---not much room for error there.


here are some examples from yesterdays shoot---tell me what you think regarding focus.


all shot with a 7D, ef500L @ f4 and the targets were between 15 and 20 feet.


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