Just Switched To Nikon, Why Auto Focus On Camera AND Lens?

Discussion in 'Digital Photography' started by 103734, Oct 20, 2008.

  1. 103734 Guest

    Apr 10, 2007
    Ok I just switched over from a Canon Rebel XT to a D90 and I got nearly everything down now and I am pretty comfortable with it now except the fact that the D90 has two auto focus switches :confused:

    Whats the point of having two? and if I want to manually focus do I need to change both of them to manual or can I just switch the one on the camera to manual?
  2. FX120 macrumors 65816


    May 18, 2007
    The D90 like it's predecessors has a built in AF motor for some of the older lenses that do not have built in AF, and the AF switch on the body controls the function of this motor.

    When useing a lens with built in AF, I believe the function of this switch is disabled.
  3. 103734 thread starter Guest

    Apr 10, 2007
    well the switch on the camera also disables the switch on the lens and vise-versa, im just worried if I just switch the lens to manual focus and not the camera if I could mess up the cameras auto focus motor.
  4. Westside guy macrumors 603

    Westside guy

    Oct 15, 2003
    The soggy side of the Pacific NW
    Could you tell us what lens(es) you have? If your lens is AF-S then you actually can manually override the focus without switching either the lens or the camera switch over to manual.

    The only exceptions to this are specifically the 18-55 AF-S and the 55-200 AF-S - Nikon used a lower-end motor in those two lenses that specifically does not allow full-time manual override.
  5. OreoCookie macrumors 68030

    Apr 14, 2001
    Sendai, Japan
    No, that can't happen. Before I explain why, here are the simple `rules':
    (1) If the lens has an MF-AF switch, use that one. Not that using the switch on the body will cause any damage, but it's easier and in one location.
    (2) If the lens does not have an MF-AF switch, use the one on the body.

    That's it ;)

    If your lens has an AF switch and you switch it off, autofocussing is disabled and nothing can happen to the focus motor. Furthermore, I assume you have an AF-S lens (Nikon's equivalent of USM) which means that the focus motor is in the lens. The kit lenses have AF-S, so if you bought a kit, you're safe. AF-S lenses allow `instant override' which you are probably used to with your Canon, i. e. after using the AF, you can engage the focus ring and the camera will stop using the AF until you release the shutter and press it half-way again.

    Second of all, even if you have another Nikon lens with an AF switch on it but with no built-in motor, the switch on the lens (which is then a mechanical switch) will decouple the focus screw in the lens (which connects to the focus motor in the camera body) from the focus mechanism. So again, once you engage MF on the lens, you're safe, nothing can happen.

    The only time you should be careful is when the lens does not have an AF switch: then you must not work against the AF. Here, you must use the MF-AF switch on the body! There are also some third-party lenses (e. g. those from Tokina) which have an MF-AF switch (you slide the focus ring back and forth) which also then couples the focus ring directly to the mechanism. This is only relevant for some third-party lenses (gets increasingly less relevant for newer lenses), older, used lenses and old lens designs.
  6. 103734 thread starter Guest

    Apr 10, 2007
    awesome answer!! all my questions have been answered! thanks!!!

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