USM/Full time manual focus... how?

[Phall82]

Hi

I have a query that I have always wondered about. I have a number of USM lenses and its always mentioned in reviews that they can full time manual focus with flicking the AF/MF switch.

I understand that you can turn the focus ring without flicking the switch but in reality, how is this useful? By this I mean, as soon as you have manually focussed and half pressed the shutter, it will automatically focus again before taking the photo.

I'm sure I'm missing something but please help.

Cheers

Colin

 

[DazJW]

You're supposed to hold the half press while manually focusing or use back button focus with the shutter half press AF disabled (better option).

 

[weybourne]

Back-button focus with no AF on the shutter button for me - it puts you in control

 

[Phall82]

I see. I knew there'd be some way of doing it with all the reviews raving about it.

Thanks for your help.

 

[poi2006]

Is the same！