A-M vs M/A-M switch

[zoltan_varro]

<p >Can someone please explain the difference between the functionality these 2 switches? Is a lens with A-M only switch not supposed to have the focus ring turned when the lens is in A mode? i.e. no manual override? If that is the case, then how come I can do manual override on my 18-105 VR with no problem while the lens has the A-M switch set to A? thanks</p>

[Matt Laur]

<p>The 18-105 is an AF-S lens, meaning that it has the AF motor built into the lens. Nikon's AF lenses allow you to have the camera AF the lens, but still allow you (while you're in A mode) to then grab the focus ring and fine-tune the focus, or just plain change it at will, as you shoot. No need to switch either the lens or the camera body to "M" to do that. <br /><br />Older lenses (the non-AF-S flavor) which have the screw-driven AF mechanisms operated by a motor in the camera body require you to physically disengage that mechanical linkage in order to manually focus the lens (otherwise you're fighting with the motor and gearing in the camera). Hence the A/M switches on those screw-driven AF lenses. It's like putting the transmission in Neutral.</p>

[ilkka_nissila]

<p>Not all AF-S lenses allow one to override focus manually without flicking a switch. I'm quite sure the 18-55 does not allow this. I haven't tried the 18-105, but Thom Hogan writes "The 18-105mm has a hybrid AF-S system, you can sometimes override the focus manually, though the camera will fight you on this more than it does on those lenses with an <strong>A/M</strong> and <strong>M</strong> switch (the 18-105mm has only an <strong>A</strong> and <strong>M</strong> switch)."</p>

<p>All the AF-S lenses I own have A/M and/or M/A and then M.</p>

[Matt Laur]

<p>True, not all AF-S lenses let you do that. But every one I use, does. 18-200, 18-70, 17-55, 70-200 (from Nikon) and 10-20, 30, and 50 (HSMs from Sigma, which provide that same functionality). On my non-AF-S lenses, I actually miss that feature rather a lot. In particular, it makes me want to upgrade my 60mm Micro ... or would, but it's just so terrific, otherwise, that I can't bring myself to put it out to pasture.</p>

[senthil1]

<p>@Zoltan - Do u mean A/M vs. M/A modes on the newer AFS lenses? On mine, one is supposed to mean easy manual override from AF, whereas in the other mode a little more effort is needed - basically, one prevents manual take over when your hand hits the focus ring accidentally; don't exactly remember which one is what, but I think A/F needs actual/intentional rotation of the focus ring/more effort. In any case, I've read reports that they are pretty much the same with no practical difference but I haven't personally tested it on mine; just keep it at A/M.</p>

<p>BTW - there's a separate M mode on those lenses, which as it explains, is just manual. So the switch gives a choice of - A/M, M/A, M. Hope this helps. </p>

[zoltan_varro]

<p>OK, so if an A-M switch fitted lens allows you manual focus override, then wha't the point of having a M/A-M switch? What additional or different functionality does that allow? thanks</p>