7DMII AF Microadjustment Variation

[Marc13579]

Hello All,

I was wondering if there is a listed tollerance for variation in AF after applying microadjustment as I'm finding that after I apply micro adjustment, there still seems to be some inconsistencies. In this example I am using my Canon 50mm f1.8. I have set my 7DMII up on a sturdy tripod and have put my Lensalign target with the ruler on another tripod. I measured out the correct distance between the camera body and the target, calibrated the height as the instructions said to do, used the middle AF point, set the camera to "mirror lockup", set the AF drive to One Shot, and using the timer function I took a three test photos to use as a base line at f1.8.  Viewing the images on my computer, I discovered that my 50mm f1.8 front focuses a little bit, but not really all that much so I apply a +3  microadjustment, and I go back to my computer to examine the results. Now it back focuses, so I decide to try a +1. I take once picture and examine it on my computer and now the adjustment is right on. That's great, but when I then take a series of test pictures with the +1 adjustment the focal plane varies, and sometimes it varies quite a bit. See these examples:

+1 Correction:

Now front focusing a little bit:

Now back focusing quite a bit:

Now front focusing:

Now front focusing more:

Now back focusing again:

I've had the camera for about a year and in general I shoot a lot of youth and high school sports and mostly at f4.0 so up to now it hasn't made much of difference. But about a month ago a did a short portrait session for a friend, and that's where I discovered the inconsistancy. So ultimatley my question is if there is a "normal" variation in AF or do I need to send my 7DMII in for repair. Thanks for your opinions.

Marc

[Waddizzle]

I assume you are using Dot-Tune.  I think you could be seeing the performance limitations of that particular lens.

While it is true, that there can be some variations in the AFMA test results, it usually shows up when performing the same tests under differing lighting conditions, not the same lighting conditions back-to-back.  Lighting conditions can significantly affect the test results, which is why Dot-Tune recommends you perform the tests at the shooting location.

[Marc13579]

"I assume you are using Dot-Tune.  I think you could be seeing the performance limitations of that particular lens.

While it is true, that there can be some variations in the AFMA test results, it usually shows up when performing the same tests under differing lighting conditions, not the same lighting conditions back-to-back.  Lighting conditions can significantly affect the test results, which is why Dot-Tune recommends you perform the tests at the shooting location."

Hi Waddizzle and thanks for the reply.

While I'm not an expert in these things, I was pretty meticulous with my test. Yes, I was using Dot-Tune. I shot all of my calibration images under the same lighting which was under ambient light with a Speedlight set up off camera diffused with a shoot through umbrella to fill out the shadows as best I could. While I thougth it might be a lens issue (these images were shot with the 50mm, f1.8 STM), I actually got similar results calibrating my 24-70 f2.8 II USM and my 70-200 f2.8 II USM. I suppose I should have included those details in the original post. 

In the end I've been happy with my 7DMII, but if there is a problem with it naturally I want to have it corrected.

Thanks again...Marc

[TTMartin]

Are you using the EF 50mm f/1.8 II or the new EF 50mm f/1.8 STM?

The EF 50mm f/1.8 II is a 30 year old lens design and most copies have inconsistent focus. If you are using the EF 50mm f/1.8 II give it to someone you don't like and buy the EF 50mm f/1.8 STM.

[Marc13579]

"Are you using the EF 50mm f/1.8 II or the new EF 50mm f/1.8 STM?"

Hi TT....the STM version. I bought it nine months ago.

Thanks...Marc

[Waddizzle]

What focus mode and shooting mode are you using?  When I have made AFMA adjustments, I do them several times under different lighting conditions, and take the average result.

[EDIT]  I get the most inconsistent results under artificial lighting, BTW, and the best results in outdoor sunlight.

[Marc13579]

"What focus mode and shooting mode are you using?  When I have made AFMA adjustments, I do them several times under different lighting conditions, and take the average result."

I shot with the drive in One Shot, using single point AF using the center point, mirror lock up, and using a two second timer to make sure that I wasn't inducing any camera shake with my hands. 

When you say "...under different lighting conditions, and take the average result", I will admit that I did not consider that. However as you can see I had quite a bit of varying under one lighting condition, so how would one take an average under different conditions?

Or...and this could certainly be a possibility...am I over thinking this?

Marc

[TTMartin · Accepted solution]

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@Marc13579 wrote:

"What focus mode and shooting mode are you using?  When I have made AFMA adjustments, I do them several times under different lighting conditions, and take the average result."

I shot with the drive in One Shot, using single point AF using the center point, mirror lock up, and using a two second timer to make sure that I wasn't inducing any camera shake with my hands. 

When you say "...under different lighting conditions, and take the average result", I will admit that I did not consider that. However as you can see I had quite a bit of varying under one lighting condition, so how would one take an average under different conditions?

Or...and this could certainly be a possibility...am I over thinking this?

Marc

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First off +1 MFA would not make a noticeably change in the focus.

Of your 6 photos there was only one were the plane of focus wasn't within the depth of field for the lens. 

I don't think there is anything wrong with your camera.

I PM'd you a link to an article done by lensrentals.com. They are a great resource, they have many copies of lenses and cameras to work with and Roger Cicala has a good understanding of how the gear works. The link I sent is just one of many articles Roger has done on AF. They are all worth reading.

[Marc13579]

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@TTMartin wrote:

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@Marc13579 wrote:

"What focus mode and shooting mode are you using?  When I have made AFMA adjustments, I do them several times under different lighting conditions, and take the average result."

I shot with the drive in One Shot, using single point AF using the center point, mirror lock up, and using a two second timer to make sure that I wasn't inducing any camera shake with my hands. 

When you say "...under different lighting conditions, and take the average result", I will admit that I did not consider that. However as you can see I had quite a bit of varying under one lighting condition, so how would one take an average under different conditions?

Or...and this could certainly be a possibility...am I over thinking this?

Marc

---

First off +1 MFA would not make a noticeably change in the focus.

Of your 6 photos there was only one were the plane of focus wasn't within the depth of field for the lens. 

I don't think there is anything wrong with your camera.

I PM'd you a link to an article done by lensrentals.com. They are a great resource, they have many copies of lenses and cameras to work with and Roger Cicala has a good understanding of how the gear works. The link I sent is just one of many articles Roger has done on AF. They are all worth reading.

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TT,

Firstly I would have thought the MFA of +1 really would not matter. But to the degree that the focus plane was shifting it was puzzling to me how or if I needed to apply more or less.

Secondly the Roger articles are clearing the above up for me. There seems to be a natural variation in focus. He uses the term "pixel peeping"; I would use the term "over thinking". 🙂  The practical position appears to be that regardless of lens/camera combination there will be a small varying of focal plane. If this is the case, then perhaps I will go back to take a few more MFA test shots and see exactly where I am at on an average. Of course this will have to be after the current soccer season (or football, depending on your location). 

Thanks much for the guidance!

Marc

[kvbarkley]

I don't know how much engineering you know, but an AF system is a very complicated control loop system involving the camera and the lens. Like all engineered systems it involves tradeoffs in speed and accuracy. Some residual error is not unheard of.

I just had something wierd happen with my T6S. I was just goofing around - I had just shot a close-up of a molting mantis - and when I pointed the camera to a concrete wall very much further away the camera indicated that it had focus when it was obvious *not* in focus. I half pressed several times and got the same indication each time. I finally pointed the camera at something else, achieved focus, and then pointed back to the wall. It focussed just fine. AF is complicated!