Would this lens for work?

Http://www.wolfcamera.com/product/CLR251666111.htm

I have a Nikon D40 and the ad says for Pentax. It seems obvious, but I want to make sure.

No, the lens mounts are different.

No. It says for Pentax…
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However… If you like this lens, ask if they have it in a - Nikon - mount…
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Most likely they do. Quantaray did when I was selling them.
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You may want to look at Amazon.com too. The price may be better.