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Honored Contributor
Posts: 5,558
Registered: ‎06-25-2014

Re: Auto Focus Microadjustment - 5D III


@Waddizzle wrote:

@RobertTheFat wrote:

There's no reason you shouldn't give it a try. But I've yet to see an "L" lens that needed AFMA.


I don't know what to think of AFMA, anymore.  If it is not needed, then what about manufacturing tolerances?  Why would a company like Sigma come up with a specialized tool like Sigma Dock?  I don't know what to think of AFMA, anymore.


Believe me, there are times when you do need it. My EF-S 17-55mm f/2.8 IS would not be usable without it. OTOH, my wife's 17-55 doesn't need it, which is lucky because she used it for several years on her T2i before I got her a 7D Mark II. I could not have used my 17-55 on a Rebel.

Bob
Philadelphia, Pennsylvania USA
VIP
Posts: 11,415
Registered: ‎08-13-2015

Re: Auto Focus Microadjustment - 5D III

"Believe me, there are times when you do need it. My EF-S 17-55mm f/2.8 IS would not be usable without it. OTOH, my wife's 17-55 doesn't need it, which is lucky because she used it for several years on her T2i before I got her a 7D Mark II. I could not have used my 17-55 on a Rebel." 

 

Yes, some correction is most definitely needed in some cases.  I'm just not certain how to determine what might be needed, and then how to best determine and implement it. 

 

The posted link the article about light explains a lot about the discrepancies and lack of repeatabiity that I have observed.  I've repeated the data gathering phase of Dot-Tune under a variety of lighting conditions as it turns out, both indoors and out.  Light sensitivity may also explain why the manuals suggest performing AFMA at the venue where you will be shooting.

 

I'm pretty sure that no AFMA is applied when the camera is in MF mode, even though the AF system may beep and report that the camera is focused.  The only way for Dot-Tune to succeed would be for AFMA values to be ignored when the camera is in MF mode.  If not, then both AFMA values should be at zero when the focus range measurements are taken.  In fact, I seem to get better results when I don't enter AFMA values until I've completed focus range measurements at both wide and tele ends.

 

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"Doctor told me to get out and walk, so I bought a Canon."
Esteemed Contributor
Posts: 4,644
Registered: ‎02-17-2016

Re: Auto Focus Microadjustment - 5D III

If you know feedback theory, you know that residual errors like this are a camera *and* lens issue, not just a lens issue.

 

Which is why pre AFMA you sometimes had to send the lens and the camera back to Canon for adjustment.

Respected Contributor
Posts: 1,119
Registered: ‎02-06-2013

Re: Auto Focus Microadjustment - 5D III


@kvbarkley wrote:

If you know feedback theory, you know that residual errors like this are a camera *and* lens issue, not just a lens issue.

 

 


Yes...definitely a combination of camera and lens.  I have different AFMA values for different cameras for the same lens.

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Diverhank's photos on Flickr
VIP
Posts: 11,415
Registered: ‎08-13-2015

Re: Auto Focus Microadjustment - 5D III

[ Edited ]

"If you know feedback theory, you know that residual errors like this are a camera *and* lens issue, not just a lens issue." 

 

I am well aware of that.  That's half the source of my doubts.  The same is true for the adjustments.  Adjustments at one end of the focal length on a zoom have an impact across the entire focal length, not just at the endpoint.

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"Doctor told me to get out and walk, so I bought a Canon."
Occasional Contributor
Posts: 24
Registered: ‎03-07-2016

Re: Auto Focus Microadjustment - 5D III

Thank you all for various input, I will very likely take a basic approach as follows:

 

  1. Adjust in 5DIII using AF Microadjustment at recommended 50x FL for both 24-70 and 70-200 at f/2.8.
  2. Use USB Dock for Sigma 35mm 1.4 at recommended zones 0.2, 0.3, 0.6m and for the last zone I shall set at 3m. And turn off AF Microadjustment.

I shall see how this will turn out to be. Hopefully I do not have serious issues with front and back focus. Will report with another post once I have a chance to work on the above. I have also completed making a DIY GhettoCAL target which I will use to ascertian front/back focus error.

 

 

Edwin Ho - Perth, Western Australia
5D, 5D III, EF 24-70mm f/2.8L, EF 70-200mm f/2.8L IS II, EF 40mm f/2.8 STM, 580 EX II
Lightroom 6, Photoshop Elements 10
And others.
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