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Old 02/16/2010, 07:14 PM   #12
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Join Date: Jan 2005
Location: Panorama City, CA
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Originally Posted by jhildebrand View Post
Looking at the Tamron 90 for my Nikon 5000 and I'm wondering what advantage is there to the one with the motor??? Some sites don't even list which version they're selling? I'm a DSLR newb and I'm stuck on this one. I thought the camera itself did the autofocus, so why would a lens need a motor?
Because entry-level cameras like the D40, D40x, D60, D5000 and D3000 don't have AF motors in the body. These cameras can only autofocus lenses that have their own built-in motor (BIM). Higher-end cameras such as D90, D70, D300, D3, etc have their own motors to drive the AF on (usually) older glasses.

To answer your question, you need the Tamron 90 with a BIM because your D5000 has no motor in the body and it will not AF the Tamron by itself.

Once upon a time, Nikon was SO BEHIND on technology that they only used (and still use to this day) the screwdriver AF, which is slow and noisy. They are now slowly catching up and has since introduced several lenses with BIM (called AF-S in Nikon speak) All newly-released Nikkors today have AF-S. The higher-end Nikon bodies still have screwdriver motors so that you can still use your OLD Nikkors. Eventually, everything in Nikon-land will have AF-S... maybe in 20 years.

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