Question
I recently bought a Canon 550D, and I read it has an auto-focus motor, which not all cameras possess. I'd like to know what it is, and what I can do to keep it running smoothly; AFAIK the manual doesn't come with instructions on how to improve the life of the focus motor.
Answer
An auto-focus motor is just what it sounds like: a small electric or piezoelectric ("ultrasonic") motor which moves the lens elements to facilitate autofocus.
In some camera systems, this motor is in the camera body, and the lens moved by a physical coupling. However, you actually read some misinformation. Canon EOS cameras do not have a motor in the body, and instead, all lenses have a built-in focus motor.
With Pentax, all auto-focus camera bodies (to date) have a motor, and some lenses have their own. (In that case, the lens motor is used.) That used to be the case with Nikon too, but in the last few years (starting with the D40), the entry-level Nikons have dropped this. That's a big deal, because it means Nikon AF lenses without a motor don't autofocus. As Nikon refreshes the lens lineup, this will be less of an issue (except if you have or want to obtain older lenses and have them autofocus) — lenses like the AF-S DX NIKKOR 35mm f/1.8G didn't exist when the Nikon D40 came out, and that's part of why the Internet was all in furor about this.
So, you often see "no focus motor" as a disadvantage for entry-level Nikon cameras. This leads to the incorrect but somewhat widespread assumption that the natural opposite (for cameras for which this is not an issue) is "has focus motor". That's technically incorrect, but the practical point is that for your camera, the lack of a focus motor is a non-issue.
And also, since there isn't one, there's nothing to worry about for maintenance. Focus motor failure isn't one of the big, highly-reported problems of cameras which do have them, and I don't think there's any particular recommended maintenance.
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