AF switching on the 7D2

[digital]

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. 

[Ricci]

Have you seen more than one expansion AF point light up in one shot drive mode?

I think that the central point is always light up and one eventual surrounding point may eventually light up, which would be the final chosen AF point.

I also believe that in all AF area modes except zones (point, point expansion 4, point expansion 8), the camera will finally focus on one point only, it is not an average or weighing of more than one AF point.

Please let us know if you find something that states otherwise.

Ricci.

[digital]

I have seen one light up for sure and while I was testing I'm pretty sure I did see more than one. I'll test that again and report. More than one point is active in zone.

That is very possible and makes sense. If the centre is lit and the outer takes over it is the active focus point until the centre can reacquire.
.
We'll see if Canon responds.

[digital]

I could not get 2 expanion points to light up today so perhaps I was wrong about that. I'm pretty sure I did see two once when viewing in DPP. Maybe I imagined it,

Today I noticed that in a poor contrast shots the adjacent AF assit point alyways lights up first followed by the centre point. On my LCD I could not see two active points and it appears only the adjacent is illuminated. I won't be able to access DPP for several days.

The manual states that the center point must acquire focus first. If it does and is not sure then it uses an adjacent point that has more contrast? If so it appears it is switching. I need to check this on DPP. I know I have seen two points but perhaps that was the center and an assist point. Perhaps DPP shows more detail than the LCD.

[Ricci]

Yes, I have never seen more than 2 AF points light up in any expansion mode, and always the center point plus an eventual adjacent one (up to 6 AF points in zone modes).

I will be looking forward to your new tests.

Ricci.

[digital]

That makes sense. It has been about 4 months since I last looked at this and I don't have DPP. Are you seeing both the center and outer point on DPP only or both it and the LCD?

When I was testing yesterday part of it was using my wifes purse that was not all a flat surface. I purposely put the centre point on a flast surface that had no contrast and made sure an outer point was on an area that had more contrast. It picked up the outer point first and then the centre point activated.

Since the manual states the centre point must achieve focus first it probably does and the algorithms have a percentage of AF accuracy and if it fails then it uses an outer point if it can. I guess the centre point actiavtes to show the intended point .

I'm going to try this in case 1 and 5 to see if anything is different. I doubt I'll ever see a difference in speed. Also some tests on angles with wide open DOF to see if it maintains the intended centre point fccus and does not shift to the outer point. Interesting to see if it just uses an outer point as a reference. Also a series of shots using the 8 expasnion points in AI Servo. View it on DPP and see if any did shfit off the centre point. I don't ever recall them doing that but I know I only see one.

It is going to be several days when I get back to civlization.

[digital]

Sorry for any typos. I'm on my wife's iPad and we have a weak and intermittent signal. It crashed on me several tiimes working on the previous post. 2 times doing thiis one. I can't take it anymore lol.

[TCampbell]

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.)