07-10-2015 11:07 AM - edited 07-10-2015 11:30 AM
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.
07-12-2015 09:59 PM - edited 07-12-2015 10:03 PM
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.
07-13-2015 10:49 AM
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.
07-13-2015 10:55 AM
According to the 7D II docs... "tracking" only works in full 65-point AF selection mode and the Zone AF selection mode (and since the 7D II actually has two variations on zone mode, I'm guessing it works on both. My 5D III only has one zone mode so I can't test that.)
If you are in spot, single point, expanded, or surround modes, the tracking is not supposed to work.
Also, the iTR on the 7D II is better than the version in the 5D III. In the 1D X and on the 7D II you can link the iTR to metering and color and it can also do face detection. There's a sensitivity setting for this if you enable the linking. The 5D III doesn't have the ability to link the iTR to metering in the same way that the 7D II can do it.
Exanded and Surround modes are variations on single-point AF (the camera still wants to use the center point) except that it gets to borrow adjacent points to help it lock focus. Particularly useful if the subject has poor contrast because you enlarge the area in which it might find enough contrast to help it lock focus. Spot AF is the opposite... it reduces the size of the single point AF but requires that the subject used to lock focus have particularly good contrast -- not suitable for poor contrast targets.
But none of these modes (Spot, Expanded, or Surround modes) claim to do tracking according to Canon documentation.
I have only used full auto-select mode when doing tracking (even though the docs state it should also work in zone AF mode -- I just haven't used it that way. -- mostly because if it does do tracking, it's only within the zone (it wont follow a subject if they leave the zone.)
07-14-2015 08:11 AM - edited 07-14-2015 08:12 AM
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 ?
07-14-2015 09:16 AM - edited 07-14-2015 09:23 AM
07-14-2015 09:01 PM - edited 07-15-2015 09:44 AM
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.
07-15-2015 10:45 AM