It has an "F" lens mount. source:
http://www.dpreview.com/reviews/nikond50/page5.asp
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It's A-mount.
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It depends on the make of the lens and the mount type. Newer
Canon lenses have an EF mount while Nikon lenses have a Nikkor
mount. Though you can purchase conversion kits to put a Canon lens
on a Nikon and vice versa.
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No, this is a point & shoot camera and there is no lens
mount. The lens is fixed on the camera and cannot be removed.