Canon EOS cameras have a user-selectable option (called custom functions or CF) that allows you to change the auto-focus operation to another button on the camera than the shutter release button. Basically instead of pressing the shutter release halfway and then have the camera focus you can press the other button for focussing and then just shoot the picture with the release. This is useful in situations where for example the distance to the subject doesn’t change.

I have struggled with CF4 lately, since trying my luck on the streets. I have had CF4 set ever since I got my 5. It’s brilliant, but in the last few weeks I was rethinking and trying out some combinations to find a new setup, because it was holding me up.

I suppose we can agree that on the street one has to be pretty quick with camera handling. Maybe just me, but when I am pressing the AE button on the back I find it difficult to press the shutter release soon afterwards (feels like changing grip a little), not to mention at the same time. So I lost a lot of time. Also using AI Servo operation, ie. AF tracking is impossible (I can’t recall whether the camera allows to do this actually), because you’d have to press both buttons at the same time, which is very unnatural.

Then I tried putting it back on the shutter release button, because after all I felt I wanted focussing most of the time. In One Shot AF mode the camera prevents you to release the shutter until focussing is completed. That can be frustrating when you think you have the moment and can’t shoot, even though you’d be willing to put up with the current focus. In AI Servo you can shoot anytime, but recomposing will also cause refocus.

Lastly I tried keeping it on the shutter release, but switching the lens between AF and MF as needed. This also didn’t really satisfy me. Sometimes I would forget what the setting was, or have to get used to switching back everything to a “base” setting. This didn’t feel ideal either and I was afraid I would be wearing out the tiny lens switch over time.

Of course one could stay permanently in MF and use the manual pre-focussing and hyper-focal techniques, but why am I running around with an AF SLR? On the other hand the 5 is an old camera and AF is probably a lot more inaccurate and slower than a recent body.