MF and AF

ethan · 5 May 2010 at 23:25

Understandably some or all modern dslr's have AF & MF on the body of the camera, but why do they also have that function on the associated lense? Sorry if this is an idiotic question.

Mr Jones · 5 May 2010 at 23:32

Makes changing settings faster. At least that's what I felt back then when I used my Canon 20D. i.e. when shooting AF, and I suddenly want to MF, just push the tab and MF away.

ethan · 5 May 2010 at 23:34

Mr Jones said:
Makes changing settings faster. At least that's what I felt back then when I used my Canon 20D. i.e. when shooting AF, and I suddenly want to MF, just push the tab and MF away.

So does changing the focus from the lense overide the settings/button used on the camera body? Thank you.

Mr Jones · 5 May 2010 at 23:36

Aye. The hardware button overrides the settings on the camera body. At least that's what happens on the Canon and even on my Olympus when I used the Sigma 30mm.

ethan · 5 May 2010 at 23:45

Mr Jones said:
Aye. The hardware button overrides the settings on the camera body. At least that's what happens on the Canon and even on my Olympus when I used the Sigma 30mm.

Cool. I've only just received this (Alpha 550) and I couldn't recall there being AF and MF on the ealier models kit lense (A100, for example). Thank you for the answer.

asim18 · 5 May 2010 at 23:54

It's because the switch physically disengages the AF motor allowing you to twist the ring. On most cheaper/kit lenses you cant twist the focus ring while the switch is in "A" position. The in-camera setting just disables the AF through "software".

You can still manually focus on lenses which have a manual override focus though.

ChazHurst · 6 May 2010 at 12:09

That lens has a built in motor. As with any Sony lens with "SAM" in it's name... not sure what it stands for, but I think it's a small low power motor. Anyway, the AF/MF switch on the lens engages or disengages this motor. The AF/MF switch on the camera will have no effect on the lens operation.

PaulyD · 6 May 2010 at 12:42

Just to confuse matters even more you can get lenses with full time manual focus (or thats what its called for Canon - not sure if its a generic term!) which means that even when its in AF mode you can still turn the focus ring as if its in MF.

Mud · 6 May 2010 at 14:08

PaulyD said:
Just to confuse matters even more you can get lenses with full time manual focus (or thats what its called for Canon - not sure if its a generic term!) which means that even when its in AF mode you can still turn the focus ring as if its in MF.

Same on Nikon, it's M/A instead of just A.

ChazHurst · 6 May 2010 at 16:02

As do Sony, my 70-300G has a feature called "Direct Manual Focus (DMF)" which works when you are in AF-A or AF-S... not AF-C though...

Mr Jones · 6 May 2010 at 18:24

Olympus E-Systems have the 'Fly-by-Wire' setup for all of it's lenses, which only focus when the body is turned on, all AF/MF is selected in body. Only a handful of which actually has a mechanically-coupled manual focus ring, much like FTM focus.