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AF switching on the 7D2

Rising Star

This would apply to anhy camera that has case numbers or the 3 parameter settings. I have owned all the crop bodies from the 20D to 7D2. Also all 3 5D and currently have the 5D3.


I am not stuggling in any way. I went out birding (in flght) a few weeks weeks ago and tried all 6 case numbers and all AF modes, single, expanded and zone. Since they were steady and non erractic I had very good succes and found zone to work quite well on this body.              


I have been curious about Canon's explanation about AF switching when it comes to expansion AF mode.


From the 7D2 manual 





The key phrase the camera switches it's focus to neighbouring AF points. My understanding is the surrounding AF points around the centre point in expanded are assist AF points. In AI Servo I never see anything switch. Ever. All I see is the centre point illuminated. Perhaps they just assist faster. If so I wish Canon would have worded it that way.


Personally I decided it does not make much sense so if I'm in Cases 5 or 6 I use zone where the AF points are actually switching. If you are tracking an erratic subject it just makes sense the more AF points involved the better. Especially in 65 AF for those really small fast birds that change directions quickly. Very difficult to track in expansion - even in 8 point.   


Of course this is just my opinion. This is the only part of that entire manual that I have always questioned. Even the Canon PDF AF guide. I keep asking in case someone has found the answer on other forums but no answer yet. 



You will never see surrounding iluminated squares on AF point expansion modes because these are not AF tracking modes as Zone AF are, even if the AF system does switch to one of the surrounding points in case it cannot focus on the central point in first term.


In AI Servo AF, the difference between AF point expansion and zone AF is that in the first case the central point is constantly used in first term whilst in the second case, the AF system continuously tracks on one or more points of the AF point inside the zone AF and these points are indicated to the user.


I hope this makes sense to you.





If I understand your issue, you need to watch this Canon Learning Center vid.  AI-Servo on 7D

EOS 1DX and 1D Mk IV and less lenses then before!

Thanks for replying. I'm not having any issues. I know this camera inside out. That is a very good video which I often post to help people when they are struggling.     


I went out birding one day - in flight. These were steady non-erratic birds. I shot in Case 1, 2, 5 and 6 and used single, expansion and zone AF modes in all the cases. All were like shooting fish in barrel and it proved Case 1 is a good solid base to start and work with if you are unfamiliar with the system.        


I'm having an issue with the instructions for case 5 and 6. First the Canon AF Setting Guidebook PDF states on page 21 that the expansion points are assist points.  


Cases 5 and 6 say that single AF is disabled and expansion modes are enabled. The only difference between case 1 and 5 is the AF switching goes from 0 to 1.


Switching to me means one thing turns on and the other off. You can clearly see this when in zone AF. I have never seen anything switch in either expansion modes. In one shot you can see an outer assist point illuminate when it assists the centre point both in the camera and DPP later but the centre point is always illuminated as well. You never see any assist point activate when in AI Servo. The centre point only is always illuminated.


I'm convinced the AF assist points are doing their job but I just question the explanation. To me they are not switching in both expansion modes, they are assisting. I can only assume that when I'm in AI Servo and using expansion AF the outer points "assist" faster or more aggressively when I switch from case 1 to 5.   


I'm just questioning how the manual, etc explains this. To me some information is missing or Canon made a mistake including the expansion modes, which are just an extension of the centre point. The key word being "switching".  


It is not a big deal as this does not affect my shooting. I always use zone when in Cases 5 and 6 anyway because it just seems to make the most sense. For faster erratic moving objects more AF points that will actually track and "switch" from one side of the viewfinder to the other helps with the keeper rate.          


To me, the " switching" term is appropiately used by Canon, because there is no combination of AF points used at the same time in point expansion AF types; it is or the central AF point in first term or any of the surrounding expansion AF points in second term.


However, I do agree that it is a little strange that the square icons on screen don't eventually turn on with point expansion AF types, this only works with AF tracking in AF zone types and I guess that for some reason, that is the just the way it works.


Maybe a Canon engineer specialist and an user of this forum can tell more on this 🙂 ?





Thanks everyone. Some good replies I have not been able to get on other sites. People are trying to tell me that in expanded the centre point will switch off when an assist point activates. How would anyone even know this. You can't see it.

Good way to explain assist as borrowing. The centre point is still active to me so it is not technically switching. When in full 65 zone and you select the farthest outer point and it a starts tracking you can see the points activate and deactivate as the subject moves across the viewfinder. The orginal AF point thrat acquired AF eventually deactivates.

When in expanded the centre point has to be on the subject at all times. The outer points assist or are borrowed when needed. Canon claims AF tracking is active in expanded so that has been my question. Do they assist or get borrowed faster?
We would nor know because you can't see this happening. When you think about that purpose of AF tracking it really does not make sense that expansion should be included but I could be wrong.

Sorry for any typos. I'm not in my element. In a remote area with poor with service using my wife's iPad.



I looked for the exact sequence of how AF point expansion works in both Canon and also external documentation.


Unfortunately every explanation I found (manual, books and web sites) only indicates that if the central AF point cannot focus, then it will use the surrounding AF points. That is what makes me think that it is like a sequence, it is not that the surrounding points works together with the central AF point at the same time.


There is no clear indication if more than one surrounding AF point works exactly at the same time.


If the AF switching term is used, then we are facing a synchronous process, not an asynchronous one, at least between the central and surrounding AF points.


In AI Servo mode, it may happen that if the central point cannot focus, it is not considered (equivalent to "desactivated" or "desabled") for a fraction of second, then the expansion AF points are analyzed with eventual focus success, and once they are processed, it will return back to the central AF point and so forth.


That is my supposition.


It would be really great if Canon can clearify us on this subject, even that the process is so fast, it really doesn't matter.





So far this is the best conversation I have had on this subject. That is intersting. When in One Shot you can see one or more expansion point that activated so I guess it can be one or more depending on how many the system needs. Also the centre point is always illuminated if an expansion point or more are required.

You can't see this in AI Servo. You can only see the centre point.. I'm convinced it is working. Why Canon chose not to show them another question but not the primary. I assume AI Servvo works the same way as One Shot.

The interesting part. I read the center point has to acquire focus first. Then if the object moves or it can't maintain focus due to poor contrast, etc one of the outer points kick in to assist. I'm out of my element. No manual or AF PDF to refer to but when I get back I'll check and we can compare notes.

Thanks for getting into this. Hopefully Canon will respond.

7D2 manual. PG 95 - AF Expansion. With AI Servo the initial manually selected AF point must focus track the subject first. Then if goes on to say when in One Shot both the centre point and expansion points will light up. No sure about exact words about One Shot. I'm in a remote loaction and it took 45 minutes to downlaod the manual and then I lost the connection before I could write it down.

Until Canon replies and considering the AF PDF states the outer points are assist points we can only assume they assist faster when AF switching is set to 1 or 2. Since I always see the centre point illuminated in both One Shot and AI Servo they never technically switch off but are active in trying to reacquire AF because they are the primary manually selected AF points.

It is not a big deal as it is not going to effect my photography. Canon could have explained that better because as you try to get the most out of a system understanding these small things can help. Using switching as a general statement was probably easier because not too many people would question this.

Of course I'm assuming they assist faster in Cases 5 anf 6 or whenever you adjust the AF switching iusing any case. That was always the primary question.

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