What is the difference between a film lens and a digital lens?

specifically Canon. Are they made differently? Can some of them if not all of them be used on both camera types (film and digital)? Are there risks using a film lens on a digital camera?|||The lenses used on 35mm, full frame Nikon and Canon digials and the Canon's with a 1.3x magnification factor (29mm x 19mm), cover a larger area (36mm x 24mm) and the standard dgital SLR has a sensor that is smaller so the lenses don't have to cover as large an area (24mm x 16mm) .Film lenses are generally more expensive than digital only lenses for this reason.





You can used any film lens on a (Nikon on Nikon, Canon on Canon, etc) DSLR.|||The differences:


Film lenses have a larger "image circle", that is, they are designed to cover the larger image area used by 35mm film. When used on a digital SLR, only the center area of that image circle will be used, commonly called the "sweet spot" of the lens. That's because lenses tend to be sharper and have better contrast in their center image circle areas.





By comparison, a lens that's made for digital SLRs will have a few differences. First, their image circle will be smaller because digital SLR sensors are smaller. This makes them generally unsuitable for film use. Second, their coatings and lenses are adjusted to get light to hit the sensor more directly, to minimize color aberrations and vignetting.





Can they be used on both camera types?


In Canon parlance, lenses suitable for both film and digital are called "EF" lenses. Lenses which are designed only for the smaller digital sensor cameras (Digital Rebel, EOS 20D, EOS 30D, Digital Rebel XT and Digital Rebel XTi) are called "EF-S". So, yes, a film lens can be used on both camera types, while the digital EF-S lenses shouldn't be used on a film camera or a digital camera with a physically larger sensor (like the Canon 5D).





Risks?


There are no risks for using an EF lens on a digital camera. Using an EF-S (digital) lens on a film or 35mm-sized sensor camera will probably give you darker edges in your image, called "vignetting."|||There are really no differences in the physical lenses except for a few of the Canon wide angle lenses (the EF-S series lenses) which were designed for only the small sensor Canon digital SLR's. These lenses will not work on the film EOS series cameras and the full frame digital cameras (like the 5D) because they sit too far back in the camera body to clear the mirror and don't have a big enough circle of coverage to cover a full frame format, so the full frame format cameras will lock out the Canon S series lenses, which are not usable with the full frame image cameras.


Also note that a 50mm focal length lens which "sees" approximately like your eye sees things on a full frame film or digital camera, is a telephoto lens on the smaller image sensor digital cameras (like the digital Rebel series cameras).|||go to howstuffworks.com to find out