10D AF System - can someone explain?

[ingenus]

I got my 10D about 9 months ago, and couldn't live with the 7 point metering system. I changed to using the centre point only, and have always been happy with the results.
The problem I had with the 7 point system was that it seemed to focus on objects in front or behind the main subject which was regularly out of focus.
Can someone explain what the advantages of this 7 point system are? Is there a correct and incorret way of using it?
I would like to use it, but can't seem to get the same quality of result as using the centre point only.
Thanks
Iain

[Cadwell]

Well, one advantage is explained here...

http://visual-vacations.com/Photography/focus-recompose_sucks.htm

[ingenus]

Thanks for that. I understand the points being made, but I'm not sure they answer my question. I'm not really talking about recomposing from a centre point measurement or manually selecting a different point, I'm talking about the automatic focus situation when the camera decides on which of the 7 points to focus on. Under these circumstances, I seem to get focus where I don't want it.
Am I missing something here?

[Cadwell]

the automatic focus situation when the camera decides on which of the 7 points to focus on. Under these circumstances, I seem to get focus where I don't want it.
Am I missing something here?

Nope... that's what it does more often than not. Basically it's not very useful. :lol:

[ingenus]

that seems a shame then! What would you recommend then as a GENERAL method of focusing on the 10D? I can see how manually selecting a point works for portraits or scenes that you can take as long as you like to set up, but what about candids or moving objects?

[Cadwell]

Well I normally leave it on centre focus point. Sometimes I select another one, but not often.

[dsze]

I leave mine on the center, but I have the assist button set to go to the point just right of center. I leave it like this all the time. The 7-point auto-system is very unreliable IMO.. For moving subjects you can used the AI Servo mode.... Or, have good light and a fast lens and focus/release all in one motion. This is typically the method I use for wakeboarding shots. I think most would agree that you get the most accurate results from the center-point.

http://home.insightbb.com/~photographs/wakeboarding/index.htm

-daniel

[ingenus]

Well, this is kind of what I thought as I get much better results from the centre spot.
So, why is there such a fuss over the 9 point system in the 20D? If the 7 is not much good, then why should 9 be any better?

[dsze]

Well, to be honest I am quite happy with my 10D and it suits my needs well, so I haven't even looked closely at the 20D. But I suspect that rather than just adding 2 extra AF points, the 20D uses a different method for auto-focusing which is supposed to be more accurate/faster. I'm sure that there are others here who can give you a much more accurate description though.

-daniel

[CyberDyneSystems]

It does not matte which point you select.. there are definatley times i use points other than the center.. what deos matter is that YOU slelect it so you know where the camera is focusing.

The issue you see is not whether the camera has 7 points or 1.. it is WHO selects which point to use :) If the camera decides.. it may not "agree" with what you would like to see in focus :wink:

[dsze]

...nice clarification...Its not that the auto system is wrong, it just may not be what you had in mind.

-daniel

[SWPhotoImaging]

I have my 10D in 7-point focus mode, but I keep the middle button by my right thumb set to shift to center point only on demand. This works very well for me when there are foreground objects in a scene that are not the intended focal point (shooting an animal through the grass or reeds, etc). I like it this way, and probably use the center-only override 40-50% of the time.

[Mark Kemp]

Its quite handy if you have a group of people to shoot and nobody in the centre. Multi point AF can usually sort that one out quite well.

Similarly, say you are shooting something big and not very flat like a building in 3/4 view. You can try to get the AF points to mostly cover the target and the AF will usually pick a pretty good focus point to try to get as many points as possible as sharp as possible. Obviously its better if you have plenty of DOF, which means a sunny day.

If you have one small target that must be really sharp and never mind anything else, then use a single AF point. Especially if you must also have a wide aperture.

If you must have multiple parts of the image sharp then use a tripod and a very small aperture, and/or do some hyperfocal distance calculations.

If you haven't time for a tripod or a lot of sums, then multi point AF can be very useful. The results may not be perfect, but if the moment would have passed otherwise they are still better than nothing.