autofocus, quick mode vs live mode

[gil]

Hi. I'm having trouble using my Canon 1100d with some autofocus shots with my EFS 15-85mm lens.
I've noticed the two alternatives of quick mode and live mode within the AF mode. Up until now I've been set on quick mode and sometimes it refuses to find the focus, jigging back and forth until I give up, particularly within say 3 metres. Was wondering if switching to live mode would help or make any difference.
Appreciate any tips
Gil

[dje]

Hi Gil

I have a 600D which I suspect is much the same as the 1100D in regard to Autofocus. In Live View mode, you have two choices for AF - Live View AF which uses contrast detection on the main sensor and Quick mode which uses phase detection on the dedicated AF sensor (the same way AF works when using Viewfinder mode). In Live View mode, the live view dis-appears momentarily while Quick mode AF takes place.

Quick mode AF should be more effective (and quicker) than Live View AF.
(although I'm not sure how they compare in low light). You could try LV af and see how it compares.)

The only suggestion I have is to set the AF point to manual selection and select the centre point. This will ensure that you have a well defined focus point but you will have to make sure you align this centre point with the subject you want to focus on during the AF process. Hold the shutter half down to keep the focus locked and re-compose the shot if necessary before clicking the shutter fully.

Dave

[gil]

Thanks Dave, will experiment with those ideas