On Digital SLR cameras lens brand?

I have a Nikon can I buy a cannon lens, will it fit even though they aren't from the same brand?

This is the situation with today's digital cameras as opposed to their film counter part's. With film SLR's "off" brand lenses could be "adapted" to another manufacturer's camera with the use of a simple adapter. Today's DSLR's are not made that way. If your purchase a Tamron lens you of course must specify what lens mount you wish the lens in. I recently purchase a Tamron zoom lens for my Pentax Kx DSLR. But their is no way this lens can be used on say a Canon or Nikon camera as no "adapters are made for that use. This is do in part that today's cameras are really "small computers with a lens". This is my phrase. But it is true in that each manufacturers lens has electrical contacts built in to match the circuitry of that specific camera brand.

Sorry No - It's like trying to fit a Round Peg into a Square Hole. So they have to be the same Lens Mount.

You can't do that.

Flange focal distance on Canon lens is 44 mm, Nikon is 46.5 mm.

So the lens won't focus on infinity, and you can't control the aperture, because EF lenses are purely electronic.

If you want, you need special adapter to correct the focus and control the aperture.