In the video world, lenses of many different brands are all compatible with a few mounts. A lot of different manufacturers make lenses in PL mount, for example, and lots of different manufacturers make cameras that accept them.
In the photo world, every brand of camera has a proprietary mount. And many brands have more than one mount. The problem gets compounded when you consider third party lenses made by Sigma, Tamron and Tokina. Each of those manufactures make lenses in Canon, Nikon, Sony and 4/3 mount, so you have to get the Sigma for Canon mount, for example.
Even within the correct mount, however, some lenses only cover crop-sensor cameras, the image circle won’t cover full-frame. The manufacturer’s often use cryptic terms to announce whether a lens covers full frame or only crop frame cameras. Canon EF lenses are full frame, for example, while Canon EF-S lenses are crop frame. Nikon FX lenses are full frame and DX crop frame. Sigma DG lenses cover full frame, DC cover crop frame. And on and on.
- Crop Frame (7D, 60D, T2i): all Canon mount lenses work
- Full Frame (5D Ml II): Canon EF lenses work, EF-S lenses do not. Most wide-angle Sigma, Tamron, Tokina lenses do not.
- Crop Frame (D300s, D90, D7000): All Nikon mount lenses work
- Full Frame (D3s): FX lenses work. DX lenses work badly. Most wide-angle Sigma, Tamron, Tokina lenses work badly.
- Alpha Full Frame (A850, A900): Not used for video that we’re aware of. Full-frame Alpha lenses work, of course.
- Alpha Crop Frame (A550, A580): All alpha mount lenses work. NEX lenses do not work.
- Sony NEX: All NEX lenses work, Alpha lenses do not.
The SLRs and cameras that are used for video are basically Micro 4/3 mount. Only Micro 4/3 lenses will mount. Other Olympus and Pansonic lenses do not work.
All those different mounts have different flange-to-sensor (or flange-to-focal) distances. A lens from a camera system with longer flange-to-sensor distances can be mounted on an adapter to a camera with a shorter flange-to-sensor distance, but not the other way. That’s why you can mount a Nikon lens with adapter to a Canon body without corrective glass elements, but not the other way around.
As you can see from the table above, Micro 4/3 and NEX cameras can use almost any other lens on the proper adapter. Nikon cameras can’t use other lenses with adapters -- except PL in theory, but we know of no adapter for that.
Most adapters do not transfer electronic controls to the lens, and many lenses have electronic aperture controls. So it may not be possible to shoot the lens other than wide open (the default). But most people shoot wide open aperture most of the time so its rarely a major problem.
The following adapters are readily available: