3. In Digital SLR Sensors Size Really Does Matter, Continued

While the magnification factor allows a lower focal length lens to masquerade as a telephoto lens, it also reduces the sweeping coverage of a wide angle lens. A 12mm lens becomes an 18mm lens with a 1.5x sensor. Though 18mm may seem wide, its images don't cut it when you need the kind of dramatic pictures you can take with a 12mm lens.

There's another advantage to smaller digital SLR sensors. As noted above, you don't need as large a circular image to cover the sensor as you do with a full size sensor. This allows manufacturers to produce lighter, smaller and potentially less expensive lenses with smaller image circles for small sensor SLRs, than the lenses required by full sensor SLRs. Though all of this sounds great, I have yet to see a lens designed for a small sensor that can produce the image quality of a lens designed for a full digital sensor and 35mm film. Part of this is because you're still fighting the lower resolution image produced by the smaller sensor. Though professional photographers are happy with what they get from small sensor SLRs, the best stuff still comes from larger sensor cameras.

What if you try to use a lens designed for a small sensor on a full frame camera? Here's the answer.

Taken with the Canon 5D and a Tamron small sensor XR DiII 18-200mm f3.5-6.3 lens at 18mm

While this is kind of funny, remember that all the less than full frame lenses you buy are going to act the same way. If there's a digital full frame camera in your future, I suggest you start buying full frame lenses. How? Just stay away from lenses with "Digital," DI," or some such terminology in their name. Lenses for Canon cameras designated "EF-S" are designed for cameras with smaller sensors. They won't work on a full frame camera except as novelty lenses.