I'm planning on getting a 20D this spring, and I'm investigating lenses I might like. I quite like the sounds of the 17-85mm IS USM lens that's available as a kit with the 20D, but I have one concern. It's an EF-S mount lens, so does that mean I would be unable to use it on a Canon film body? I'd like to get a film body (at some point) for backup, and I'm planning to start doing wedding photography. I would like to make sure all my lenses will work on both bodies.

The EF-S lenses cannot be used on film bodies, in fact they can only be used on some of the DSLRs like the 20D and the Digital Rebel.

Danielle

Mig is correct. The EF-S lenses are designed to work only with specific Canon digital SLRs. Currently, they're only compatible with the EOS 20D and the Digital Rebel. There are two compatibility issues. The first is that the image circle is smaller. Since they're made for use with the smaller digital sensors, you'd get some serious vignetting with your Canon 35mm film camera. The other problem is the rear element placement. This is also the reason the EF-S lenses aren't compatible with the EOS 10D. The rear element is closer to the sensor/film plane on the EF-S lenses. The rear element on an EF-S lens would actually make contact with your film camera's mirror - probably damaging the lens and your camera.