Focus Point Confusion

I get the following question rather  lot – so when another reader asked a few days ago, I thought “let’s answer for everyone”.

When shooting, I usually use the center focus point (Canon 40D) to select what I want to focus on, press halfway and then recompose. I have recently gone through some pictures I have taken with Aperture 3, and have clicked “show focus points” and it shows that my focus point was off. It appears as though my camera did not lock the focus. I have done some research on different forums to find out what the problem could be, and some people discussed the modes “AI Servo, AI Focus, One Shot”… Should this affect the focus lock? Would I be better off changing which of the 9 focus points I wish to use for each shot rather than locking and recomposing? (I would rather not since it’s more time consuming!)

A-ha.

You are fine. You are using “one shot”, or you would not see a focus point displayed. You see, the “display focus point” function is only useful if you do not recompose, since the computer doesn’t know you recomposed. So the computer shows which point you used, but not where it was when you shot.

I.e. There’s no problems. The image is sharp where you wanted, right?

Your other question: yes, although the centre point is more sensitive, and is sensitive to both vertical and horizontal lines, it is usually more accurate to move the focus point. You can make this easier on many cameras by custom functions. But unless you are shooting with very narrow depth of field, you can usually get away with using the centre point and recomposing.

 

5 thoughts on “Focus Point Confusion

  1. I’ve used the center point focus/recompose technique but ran into a problem yesterday while trying to spot meter on a flower in the sunlight/shade. I’ve configured my 1D4 to use the back * button to focus and the shutter release button to meter. (I’m a sports shooter and the back button focus with AI Servo increases my keeper rate by 50%)

    When I recompose off of the subject the metering was now set for the new area instead of the original focus point, so now I have to get back into the camera and set the shutter release button to start/lock metering. UGH! I’ll be looking at my camera tonight after work but was wondering if you knew if the metering lock was possible?

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