Will my old Sigma 70-300mm DL Macro lens work on a dslr camera?

Your wife's EOS Rebel uses the "EF" lens mount. Canon DSLR cameras use the "EF" lens mount. So as long as you buy a Canon DSLR you can use your wife's Sigma 70-300mm zoom lens.

In my opinion you'd be smart to learn to use her EOS Rebel before buying a DSLR. The transition will be much easier plus you'll learn good photography habits by starting with a film camera.

Have you tried it? Certainly it will fit your D5000, but whether it will auto-focus is the question. You can simply attach it to your camera and try shooting a few shots. Your D5000 requires lenses that have auto-focus motors in them. If the Sigma lens has that feature it will work, otherwise you will have to manually focus the lens using the electronic rangefinder in the cameras viewfinder - page 156 of your user manual

Technically, it should work with all Canon dSLR's. In reality, you may encounter problems especially with older camera models.

Hi

The lense will work on any camera digital or film, the only thing is that the connection to the camera body has to be the same.

You may be able to get an adaptor, if its not the same.

Regards

John