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FORUMS Canon Cameras, Lenses & Accessories Canon EOS Digital Cameras 
Thread started 03 Jul 2018 (Tuesday) 17:34
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Canon AF zone focus algorithm issue

 
digital ­ paradise
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Jul 11, 2018 09:38 |  #31

This is good read as well. This is probably where you got your AF point illustration Greg. I like the section “Precise” is not the same as “accurate!”

http://www.learn.usa.c​anon.com …ticles/2014/spo​t_AF.shtml (external link)


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Jul 11, 2018 10:15 |  #32

This shows the 7D2 AF sensor array as well which is always fun when talking about this topic. Also helps to describe why some sensors are sensitive to certain geometric "shapes" over the others, which complicates analysis if you are too general about AF point discussions.

https://www.imaging-resource.com …-mark-ii/Z-7d2-65ptAF.jpg (external link)


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digital ­ paradise
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Jul 11, 2018 10:15 |  #33

Since we are having a good discussion on this I have read that when in expansion the outer points flip around and some have referred to it as mini zone. I never bought into that. If I want my AF points flipping around without dedicated AF then I would just zone AF.

First I based that on my tests using One Shot where if an outer point was called upon the centre would always light up as well. This tells me that even if an outer point is kicks in to assist the centre is still working. While we can't see it AI Servo works Canon says AI Servo works the same way. As a user that is the way I"d want to work. In expansion I'm still working with the centre point. The outer points are even smaller in the viewfinder I think to help the user keep the centre point on the desired part of the target.

You can find this in the middle of page 2 with the link below.

With AF Point Expansion active, it's important to remember that the AF system still expects to perform most AF tasks using a single AF point – that is, the principal point the user has manually selected (again, it's indicated on-screen with the larger, central AF point visible, surrounded by smaller AF point icons). The remaining points in the expanded area are usually waiting to be called into action, but only if the principal point has trouble continuing to track or find the subject you're shooting.

http://www.learn.usa.c​anon.com …_multiple_af_po​ints.shtml (external link)

I think that of an outer point is called upon in AI Servo it just telling the centre point you are still OK. It still uses the centre point as primary. This is possibly why we never see what outer point kicked in to help the centre on the LCD or in DPP.

If it actually works like mini zone why didn't Canon just call it mini zone. So if I ever wind up sitting beside Rudy Winston on a plane I'll only have two questions. The actual effects in expansion and chaining AF switching speeds. Why did Art Morris say what he did on made for Canon birding video. Does expansion AF work like a mini zone or is the centre point always the primary and just getting help from the outer points. These two questions are not critical or a make or break situation I don't think but I have always found these topics interesting.


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Jul 11, 2018 11:47 |  #34

Sorry for going off topic. I said is always updating documentation the 1DX II AF guide being one example. Focus being a topic this is the latest and in my opinion the best MFA document to date. One of my early beefs was there was no consistency between the manual which warns about using it and earlier Canon instructions. Kinda wishy washy.

Page 5 of the PDF and the first time Canon comments about the light source. Figured this might help someone.

http://www.learn.usa.c​anon.com …oadjustment-landing.shtml (external link)


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Jul 11, 2018 13:50 |  #35

Great input from everyone on this thread. I want to be clear that I wasn't disagreeing with digital paradise on the functionality of the expansion points - I've done pretty much the same test and gotten consistent results. But it's apparent to me that trying to use them in a real world setting where your foreground and background are constantly changing leads to results which are sometimes maddeningly inconsistent. The result of user imprecision? Likely so, but still something to be aware of when trying to make full use of the AF.


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Jul 11, 2018 14:12 |  #36

GregDunn wrote in post #18660660 (external link)
Great input from everyone on this thread. I want to be clear that I wasn't disagreeing with digital paradise on the functionality of the expansion points - I've done pretty much the same test and gotten consistent results. But it's apparent to me that trying to use them in a real world setting where your foreground and background are constantly changing leads to results which are sometimes maddeningly inconsistent. The result of user imprecision? Likely so, but still something to be aware of when trying to make full use of the AF.

It is all good. It is not about disagreeing. It is about trying to interpret want Canon says and sometimes two articles can say something different. It is about reading, talking and deciding how it works best for you. it is good to ask questions.

Canon sometimes has two sets if instructions or should be brave and say they makes a mistake from time to time. My new lens is not inexpensive and the method they describe to mount the strap is unusual. I tried that with the Strap Keeper just slid around. I could have ran the end through again. However Canon has a separate document on how to attach to the body which makes more sense to me.

https://support.usa.ca​non.com …14697&cat=6558B​&actp=LIST (external link)


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Jul 11, 2018 14:15 |  #37

I also got a new UpStrap and they recommend the keeper to be placed in the same spot and I have seen this in other instructions.

http://www.upstrap-pro.com/attach_diagram​.html (external link)


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Jul 11, 2018 14:17 |  #38

I don't know. Maybe Canon likes it better with the keeper on the other side for a reason. The point was two similar mounting methods were described differently.


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Jul 12, 2018 04:42 |  #39

Two different authors, perhaps?

Although some of Canon's manuals are a bit confusing, there's no doubt about the difference between single point with expansion points, vs. a zone configuration.

  • With a single point with expansion, the camera will attempt to focus with the selected, single point. Only if that's not doable, it will extend its attempt to the expansion points. If that's successful, it will display the original points as well as the expansion point as active, to show that this operation came from the selected point and was expanded to the surrounding one.
  • With zone, even the initial attempt to focus may be with any point, which can see a good contrast. There may be a useful contrast in the center of the zone, but it can still pick another AF point in the zone to begin with.

At least this is the way it's supposed to work. Tests in real life may of course, due to variations in all setups, sometimes give a different result. But I've seen the system behave according to these principles.

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Jul 12, 2018 05:23 |  #40

You can see that using One Shot in the viewfinder in real time.

With a single point with expansion, the camera will attempt to focus with the selected, single point. Only if that's not doable, it will extend its attempt to the expansion points. If that's successful, it will display the original points as well as the expansion point as active, to show that this operation came from the selected point and was expanded to the surrounding one.


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Jul 12, 2018 18:47 as a reply to  @ apersson850's post |  #41

I only see the expansion points when I don't have the AF-ON pressed. I've tried all the options for "show focus points" without success. I do use AI Servo, though, and I think that's the way the 1D bodies behave...


Canon 1Dx | 5D3 | 7D2 | 6D | 70-200L f/2.8IS | 70-200L f/4 | 24-70L f/2.8 | 24-105L f/4IS | 100-400L f/4.5-5.6IS | 17-55 f/2.8IS | 50 f/1.8 | 28-105 f/3.5-4.5 | 4x Godox AD360

  
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Jul 12, 2018 21:42 |  #42

You won't see any expansion points illuminated with AI Servo in the viewfinder or later like in DPP.


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Canon AF zone focus algorithm issue
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