With the 35mm-type DSLRs, things are fairly simple: There are a number of models, and each comes with a built-in sensor. The medium-format DSLRs vary. Some cameras are like the 35mm-type models, with built-in sensors, but others can accept a wide range of interchangeable digital backs (which hold the sensor). With the latter, you can choose a body that suits your needs, and a back, and then upgrade either as your needs or the technologies change. Obviously, be sure to check that the back and body are compatible before making purchases. These cameras are huge investments, so renting one before you buy is a good idea. Several medium-format manufacturers have pre-buy demo programs.
In this article, we’ve identified the current top-of-the-line DSLRs, both medium-format and 35mm-type models, and we’ve broken out their key strengths. We’ve also identified cameras that are one rung down, but still have many of the key attributes of the top-of-the-line models. Depending upon your needs, these "also consider" models can do what you need at considerable cost savings.
Each manufacturer incorporates its own design philosophy to create a camera that meets the priorities of its users. Depending on what you shoot, one manufacturer is probably more aligned with your needs than another. There’s no such thing as the perfect camera just like there’s no such thing as the perfect car. And when one attempts to make a car that can do it all, the results are more like a "Homer" (you can look up this somewhat obscure reference to The Simpsons) and less like a Porsche 911. Before making a big purchase of a top-level DSLR, evaluate your needs carefully to make the right decision.
CANON EOS-1D X
Quick Summary: The EOS-1D X is Canon’s flagship pro DSLR, with a full-frame (36x24mm), 18.1-megapixel CMOS sensor and the most rugged construction in the Canon line. The relatively low pixel count makes possible very rapid shooting and excellent high-ISO performance. The camera can use all EF (but not EF-S APS-C) lenses, which currently number around 60, from an 8-15mm fisheye zoom and a 14mm superwide to a 800mm supertelephoto, including many with built-in optical image stabilization, plus four manual-focus TS-E tilt-shift lenses and the MP-E 65mm ƒ/2.8 1-5x macro.
Special Strengths: The EOS-1D X is especially well suited to action, photojournalism and low-light shooting, but is a great all-around camera, too. It can shoot up to 38 RAW or 180 JPEG full-res images at 12 fps with AF for each frame. The AF system is Canon’s best, and can function in light levels as dim as EV -2 and with lens/teleconverter combos as slow as ƒ/8. It’s a great low-light camera; normal ISO range is 100-51,200, expandable to 204,800. The shutter is rated at 400,000 cycles. The EOS-1D X also has pro video capabilities, including All-I and IPB compression and Rec Run and Free Run timecoding (and, of course, the selective-focus depth-of-field control the big full-frame sensor provides). Estimated Street Price: $6,799 (body only).
Also Consider: Canon EOS 5D Mark III. The latest version of the camera that started the full-frame DSLR video craze, the EOS 5D Mark III has excellent video capabilities for a DSLR, along with the highest megapixel count among EOS cameras (22.3). It has the same basic AF system as the EOS-1D X, but with a top drive rate of 6 fps, and 63-zone metering rather than the EOS-1D X’s 252-zone metering. The 5D Mark III is also much smaller and lighter: 6.0×4.6×3.0 inches and 33.5 ounces vs. the 1D X’s 6.2×6.4×3.3 inches and 47.3 ounces. Estimated Street Price: $3,399 (body only).