10D focus settings

[always_learning]

I'm a new 10D owner, and have learned a lot from this forum. I'd like to ask a basic focus question. Why would I ever use anything but the single center-square focus? I notice that if I use the "all squares" setting, the camera finds edges in the picture at seemingly random places and focuses on them . I usually want to focus at the center, and when I don't I just lock focus and recompose.

Put another way--when should I use the all-squares setting to focus?[/img]

[nosquare2003]

I use a D60 which has only 3 focus points and save this trouble 8)

Well, I seldom activate all the focus points. One thing to note for lock focus and recompose is certainly using flash. The ETTL is focus sensitive and it starts the flash exposure calculation when you press the shutter. Therefore it will be a problem for lock focus and recompose.

[rick barclay]

http://www.flashdaddee.com/forums/showthread.php?s=&threadid=9124

I'm certainly no expert on these things, but looking at the pictures
in the above link might give you one example of a situation where you
would want to use all your focus points. I took those pictures with a
Digital Rebel with kit lens on full auto using all seven focus points. I think
if I had taken the same photos using a high speed lens at full aperture
with just the center focus point activated there would have been some
resulting bokeh which I would not want in that type of situation. I'm
sure there are other pictuesque situations where a creative photographer
would try shooting with different focus points in order to achieve interesting results.

[PaulB]

always_learning

The 'all focus points active' setting can be valuable when you are in AI Servo (or AI Focus) focus mode, the camera is then able to calculate the movement of the subject within the frame and adjust the focus point accordingly if the subject moves away from the centre point.
I agree that in normal use on static subjects having all focus points active can lead to the camera selecting some strange areas to lock focus on - for this reason I rarely use it, prefering the centre point only even for fast moving subjects 9motor sport etc.). I have however used all points active with success on aerobatic aircraft, where the movement within the frame can be a little hard to predict and keep the centre point locked on at all times.

To Rick,

Huh?
You have bokeh whatever lens you use unless everything in the image is in focus. Bokeh just being an interesting way to describe the way a lens renders out of focus areas of an image.
Use of just the centre point, or the 'all points active' setting will not alter the bokeh of a lens at all, bokeh is fixed and depends upon the construction of the lens (especially the number of blades in the aperture diaphram), the aperture the lens is set at and the amount by which the (usually) background is outside the area of focus.

[Tom W]

I use a D60 which has only 3 focus points and save this trouble 8)

Well, I seldom activate all the focus points. One thing to note for lock focus and recompose is certainly using flash. The ETTL is focus sensitive and it starts the flash exposure calculation when you press the shutter. Therefore it will be a problem for lock focus and recompose.

I posted about that very subject here. I was lucky enough to have some photos to help illustrate how E-TTL follows the focus point at the time the shutter is fired.

See this:
http://www.photography-on-the.net/forum/showthread.php?t=26304

[nosquare2003]

Thanks Tom. Your explanation is much better. :P

[always_learning]

Thank you all for most informative replies. Tracking motion and flash seem to be the two reasons to use the 'all squares' focus. The links provided by several replies are very helpful.