Group AF.

Anyone find Canon group AF largely useless with lenses 2.8 or faster?
My camera always seems to pick the closest point which makes things look like I have a front focus issue.

I have been trying AF expansion both 5 and 9 points with very little success for things like birds and butterflies.

It is possible I'm just not much good with cameras and maybe should consider pottery as a pastime instead.

fordmondeo wrote in post #18902198
Anyone find Canon group AF largely useless with lenses 2.8 or faster?
My camera always seems to pick the closest point which makes things look like I have a front focus issue.

I have been trying AF expansion both 5 and 9 points with very little success for things like birds and butterflies.

It is possible I'm just not much good with cameras and maybe should consider pottery as a pastime instead.

I need to refine my reply:

With the single point expansion modes (1 point with 4 surrounding points, 1 point with 8 surrounding points), the AF is supposed to prioritize the center point, and if that fails to lock it then enlists the surrounding points in an attempt to lock focus. If your center point is placed over a spot on the subject that the AF can grab onto, you should be good because the outer points won't be necessary. Also, the AF point type still matters: for example, if that center point you've selected isn't a cross-type point, and it fails to focus on a poorly lit or low contrast subject, the surrounding points may engage and grab focus on something you did not intend.

The 5 point expansion mode is what I primarily use for my birding, when the center point could miss if the bird darts to the side or a part of the bird with low contrast gets moved under my selected point, and the surrounding points act as a safety net of sorts. For my large aperture primes (50/85/135), I definitley only use Spot AF, since DOF is so narrow and I want the plane of focus to be exactly where it needs to be. Can't let the camera decide to focus on the nose and blur the eyes, for example.


My previous reply, I had thought you meant Zone AF, which will always grab focus on whatever is closest. This works if you're shooting with ample DOF to cover the subject or you don't necessarily need exact focus placement. If I'm trying to hit a precisely focused shot, no way am I going to let the camera make that decision for me, so I use Spot or Single and place the point exactly where it needs to be.

Zone AF can work well, if you have problems keeping a single point on the subject, and the subject is actually the closest object. Like a runner quickly passing, with nothing but the background, further away, to compete for the camera's attention.

john crossley wrote in post #18902216

[ HOSTED PHOTO DISPLAY FAILED: ATTACH id 991094 has been deleted. ]

This is useful knowledge, yet pertains to using all of the AF points in auto; OP is asking about the single point expansion modes.

MatthewK wrote in post #18902203
I need to refine my reply:

With the single point expansion modes (1 point with 4 surrounding points, 1 point with 8 surrounding points), the AF is supposed to prioritize the center point, and if that fails to lock it then enlists the surrounding points in an attempt to lock focus. If your center point is placed over a spot on the subject that the AF can grab onto, you should be good because the outer points won't be necessary. Also, the AF point type still matters: for example, if that center point you've selected isn't a cross-type point, and it fails to focus on a poorly lit or low contrast subject, the surrounding points may engage and grab focus on something you did not intend.

The 5 point expansion mode is what I primarily use for my birding, when the center point could miss if the bird darts to the side or a part of the bird with low contrast gets moved under my selected point, and the surrounding points act as a safety net of sorts. For my large aperture primes (50/85/135), I definitley only use Spot AF, since DOF is so narrow and I want the plane of focus to be exactly where it needs to be. Can't let the camera decide to focus on the nose and blur the eyes, for example.

My previous reply, I had thought you meant Zone AF, which will always grab focus on whatever is closest. This works if you're shooting with ample DOF to cover the subject or you don't necessarily need exact focus placement. If I'm trying to hit a precisely focused shot, no way am I going to let the camera make that decision for me, so I use Spot or Single and place the point exactly where it needs to be.

You have grasped what my inane ramblings mean.
I use the centre spot double cross type AF point for large less dynamic subjects.
When birding for example, I often struggle to keep a single spot on a birds eye which is why I try AF point expansion to grab something in the frame.

Sadly it always appears to use the AF point where the subject is closest to me.

I have tried all of the pre-defined AF cases with, in truth, no real discernible difference.

For clarification, I'm using a 1dx2 with 300 2.8 mk2 and 1.4 extender mk3.

Oddly enough, things improve (slightly) with the 1.4 extender over the base optic.

Isn't the improvement when using the extender simply that you cover less of the target with the few points you use? So more of the relevant part of the target is covered by the AF points, and less of the not so relevant parts?

apersson850 wrote in post #18902280
Isn't the improvement when using the extender simply that you cover less of the target with the few points you use? So more of the relevant part of the target is covered by the AF points, and less of the not so relevant parts?

Quite possibly and maybe I'll look into that more.

fordmondeo wrote in post #18902265
You have grasped what my inane ramblings mean.
I use the centre spot double cross type AF point for large less dynamic subjects.
When birding for example, I often struggle to keep a single spot on a birds eye which is why I try AF point expansion to grab something in the frame.

Sadly it always appears to use the AF point where the subject is closest to me.

I have tried all of the pre-defined AF cases with, in truth, no real discernible difference.

For clarification, I'm using a 1dx2 with 300 2.8 mk2 and 1.4 extender mk3.

Oddly enough, things improve (slightly) with the 1.4 extender over the base optic.

Maybe you need to micro-adjust the focusing.
Uploading an image showing the problem would be useful, preferably a RAW so we can see the focus points.

Mr Crossley.

I'd really like to do that but, I am internet/computer illiterate.

I am happy to email an example to anyone (the limit of my computing ability) that's interested assuming they want to give out their mail address.

fordmondeo wrote in post #18902708
Mr Crossley.

I'd really like to do that but, I am internet/computer illiterate.

I am happy to email an example to anyone (the limit of my computing ability) that's interested assuming they want to give out their mail address.

Well, with all due respect, if you are internet/computer illiterate, how the hell did you manage to find and join this forum?
How the hell did you manage to make 1153 posts?
And how the hell did you manage to upload 5 images to your gallery?

john crossley wrote in post #18902717
Well, with all due respect, if you are internet/computer illiterate, how the hell did you manage to find and join this forum?
How the hell did you manage to make 1153 posts?
And how the hell did you manage to upload 5 images to your gallery?

I'm not sure I like passive aggressive comments like yours.

You are bold enough to presume I don't have family members, friends or others to guide me through these things.

I suggest, as we say in England, you wind your neck in.