Will a 35mm f1.8d lens fit on a nikon d3100?
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Will a 35mm f1.8d lens fit on a nikon d3100?
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Of course if it has the correct Nikon mount.
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Yes, it will fit.No, it won't autofocus on a D3100 since the D3100 doesn't have a built-in focus motor required for autofocusing on Nikon's AF-D type lenses.
You'll either have to manually focus a D-type lens on a D3100, or you can buy the newer G-type equivalent that doesn't rely on a focus motor in the camera body itself.
Nikon's 35mm f/1.8G DX (DX means the lens is optimized for so-called APS-C sized sensors, like the one in your D3100) will give you auto-everything on your camera.
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AF-S DX NIKKOR 35mm f/1.8G
http://www.nikonusa.com/...s-Overview
And yes, it does autofocus with your D3100
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Yes, if it is a Nikkor (Nikon) lens or any of the third party lenses (Sigma, Tamron, etc.) with a Nikon mount.
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Yes, it will fit.No, it will not autofocus on a D3100.