VideoInterestingly, video performance and capabilities seem to be more related to newness than to the level of a DSLR. Nikon's entry-level D5100 has better video capabilities than the pro D3S (the top-of-the-line D3X doesn't even have video), and Canon's entry-level EOS T3i has better video capability than the $2,600 EOS 5D Mark II—in both cases because the entry-level model has newer technology.
If you're buying a DSLR primarily to make videos, you're probably making a mistake; but if you just want the added capability, newer DSLRs are better pretty much across the spectrum.
ViewingYou'd expect pro DSLRs to have better LCD monitors than lower-end models, but the age of the design comes into play here, as well. For example, Canon's four-year-old, $6,999 EOS-1Ds Mark III has a 230,000-dot LCD monitor, while its top entry-level model, the much newer $799 EOS T3i, has a 1,040,000-dot monitor that even tilts and swivels. None of the $5,000-plus pro DSLRs offers a tilting LCD monitor. If you do a lot of high- or low-angle photography or video, a tilting monitor can make life easier and may steer you toward a lower-end DSLR that has one (the pro-spec, mid-level Olympus E-5 has a swiveling LCD monitor).
The pro DSLRs have better optical viewfinders than lower-end DSLRs, especially the entry-level models. Pro finders feature glass pentaprisms that are bigger and brighter than the pentamirror finders used in entry-level cameras, and the pro viewfinders show 100% of the actual image area for precise compositions. Some of the mid-range models also have glass pentaprism finders with 100% coverage.
FormatMost top-of-the-line DSLRs are full-frame models, with sensors measuring 36x24mm—the same as a full 35mm film-image frame. This provides some advantages; lenses frame just as they do on 35mm SLRs for photographers coming to digital from long experience shooting film.
The smaller-sensor mid- and lower-end cameras offer benefits, however. They're much smaller and lighter than full-frame models, and their smaller sensors crop into the full image produced by a full-frame lens, decreasing the angle of view and turning a 300mm lens into a 450-480mm equivalent. This lets the smaller-sensor camera user get those dramatic close-ups with much lighter, less costly gear. A 300mm ƒ/4 lens costs around $1,500; the 500mm ƒ/4 required to provide equivalent framing with a full-frame DSLR costs four to five times as much and is much bulkier.
In days gone by, the smaller-sensor user was at a disadvantage when it came to wide-angle work because that same crop factor effectively turns a 28mm wide-angle lens into a 42mm normal lens. But today, all the camera manufacturers and major independent lensmakers offer true wide-angle lenses designed specifically for the smaller sensors, including some pro-oriented ones.