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How do camera body motors compare to in-lens motors for focusing?

I am planning to buy a Nikon D5100 camera. However, when I compare it with the Nikon D90, one difference I see is that the Nikon D90 has a in body integral AF motor while the D5100 lacks this and has to use the motor in the lens ? What are the main advantages/disadvantages of having an in body focus motor ? Does this really matter much in the quality of the photos to be clicked ?


2 Answers 2


Most significant difference is that lenses without built-in focusing motor (all except AF-S and AF-I) can only be used with manual focus when neither body or lens has motor for AF. While newer lenses tend to be AF-S and therefore auto-focusing, there are still many older ones around.

Other differences are already discussed in another question.


You must use lenses with internal focus engine to have auto-focus, which means the Nikkor lenses with letter G (like this one). If you use older Nikkor models with the letter D (like this this) you'll be stuck with manual focus.

Usually lenses with autofocus engine focus faster and quieter than those that use camera's focus engine, but are a bit more expensive and slightly bigger.

  • 1
    \$\begingroup\$ Information in first paragraph is incorrect. G means "gelded" - those lenses do not have aperture ring. D means the lens communicates distance information. Neither letter has anything to do with auto-focusing mechanism. For counterexample, AF 10.5mm f/2.8G will not auto-focus on a D5100, and AF-S 17-35mm f/2.8D will. \$\endgroup\$
    – Imre
    Commented Jun 28, 2011 at 18:36
  • \$\begingroup\$ You're right. What I meant was generally speaking G lenses usually have internal auto-focus engine. \$\endgroup\$
    – t3mujin
    Commented Jun 29, 2011 at 9:07
  • 1
    \$\begingroup\$ I'm extremely skeptical that Nikon actually means for the G to stand for "gelded". \$\endgroup\$
    – mattdm
    Commented Nov 10, 2011 at 12:45

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