How to know which lens will fit my nikon d3100?
I want a 50mm lens but not sure how to tell which will fit my camera. I'm happy to buy second hand.
ANY Nikkor AF-S lens will work on your camera
They are listed on page 167 of your user manual
You can find used lenses on B&H Photo, Adorama and KEF websites
Nikkor 50mm f1.8 AF-S will fit & autofocus.
Nikkor 50mm f1.8 AF will fit but is manual focus only (cheaper lens than AF-S version).
Your D3100 will mount and meter with any Nikon AF or AF-D lens.
With any Nikon AF-S lens (and comprable Tamron, Tokina, & Sigma optics) you'll have full compatibility, including autofocus.
Here's a current list of lenses what are perfect matches for your D3100.
http://en.wikipedia.org/...cus_motors