We're bringing you information on lens compatibility in three parts, starting with understanding the two basic types of digital SLR sensor sizes and the appropriate lenses to use.

You either have a full frame sensor, or a digital sensor that is smaller in size referred to as a APS-C (Advanced Photo System type-C). Typically, the higher-end pro cameras have the full frame sensor and the mid-range to lower end digital SLRs have the APS-C sensor. Depending on which type of camera you own determines which types of lenses will work on your camera body.

Sensor size comparison chart

Canon: Their APS-C type lens mount is called EF-S. The lenses that are specifically designed for these cameras will be marked with EF-S on the lens, and have a small white square near the mount. Canons film lenses are EF, and have the typical red dot near the mount.

Canon digital SLR mount with mounting spots for EF-S and EF lenses
Canon EF-S lens mount (white dot)
Canon EF lens (red dot)

With Canon, both EF-S lenses and EF lenses will work on the APS-C cameras. On the full frame and film cameras, only the EF lenses will work (EF-S lenses won't even mount onto a full frame or film body). Canon manual focus lens mounts are not interchangeable between AF and digital either.

Nikon: Distinguishes its digital APS-C lenses with DX. All Nikon lenses (both DX and non-DX) will physically fit onto any other Nikon mount including both digital sizes and 35mm film.

Even though Nikon's APS-C lenses will mount onto film bodies, they will not cover the full image size. This can cause vignetting or soft focus around the edges of the image, especially at the widest of the lens zoom range.

Because of the design of the sensor of a digital camera, there are more light rays reflecting back through the lens than 35mm lenses. Digital-only lenses (or APS-C designated lenses) have specially designed coatings to absorb stray light and preserve image contrast and are also typically lighter in weight.

If you're using a full frame/film lens on a APS-C camera, another thing to keep in mind is that the focal length and crop factor changes. A 35mm lens that is mounted to a full frame camera will provide a slightly wide-angle view, while when mounted to an APS-C camera will provide a slightly telephoto view. (You can read more about crop factor here, or stay tuned for more info. and example photos on Friday).

Other APS-C lens designations:
* Pentax DA
* Sony DT
* Sigma DC
* Tamron Di II
* Tokina DX

Stay tuned for parts 2 and 3!