One major selling point of a DSLR is the ability to use a wide range of lenses. All of the cameras we cover in this article have full systems behind them, including extensive lens choices, accessory flash and other useful tools. The two full-frame cameras, the Canon EOS-1D X and the Nikon D4, meet this need extremely well. Both manufacturers produce lenses from superwide-angle and even full-frame fisheye to supertelephoto, including true 1:1 macro and tilt-shift lenses. Note that as full-frame cameras, the EOS-1D X and D4 are designed for full-frame lenses: If you mount a DX lens (designed for the APS-C format) on the D4, it automatically crops the image to DX format; you can't mount an EF-S (APS-C) lens on the EOS-1D X.
As APS-C-format cameras, the Sigma SD1 and Sony SLT-A77 can use any of their lenses, with a 1.5x "crop factor." Sigma has been known as a high-quality lens maker for decades and offers a wide range for the pro SD1—from circular fisheye through 800mm supertele, including true 1:1 macro lenses. The SLT-A77, like all Sony DSLRs, can use the full line of Sony A-mount lenses, plus legacy Konica Minolta Maxxum lenses, providing a wide range of focal lengths (albeit, as is the case with Sigma, no tilt-shift lenses).
Canon, Nikon and Sony offer a good selection of electronic flash units for their DSLRs, including macro units. Sigma offers fewer flash units, but certainly enough to do pro flash photography. All offer PC contacts to connect studio flash systems. Maximum flash-sync shutter speed for the EOS-1D X, D4 and SLT-A77 is 1⁄250 sec.; for the SD1, it's 1⁄180 sec. All offer high-speed sync with compatible accessory flash units. While pro DSLRs generally don't have built-in flash units, the SD1 and A77 do.
The SD1 and A77 offer accessory battery grips, which provide space for an extra battery to extend shooting capacity, as well as more comfortable operation in vertical-format shooting. The EOS-1D X and D4, in effect, have such grips built in.
Are EVFsSuitable For Pros?
Traditional SLR and DSLR cameras have eye-level pentaprism optical view-finders. A reflex mirror in the camera body reflects the light from the lens up to a focusing screen and onto the pentaprism (pentamirror in cheaper cameras), which provides a right-side-up and laterally correct image of the actual image formed by the lens. When you fully depress the shutter button to make an exposure, the reflex mirror flips up out of the light path so the light can reach the film or image sensor.
This system has a few drawbacks. First, the viewfinder image blacks out during exposure because the mirror is in the up position rather than the down viewing position. Second, the mirror's movement creates vibration, which can adversely affect image quality. Third, conventional phase-detection AF systems require the mirror to be in the down (viewing) position to function, so you have to use slower contrast-detection AF in Live View and video modes. Finally, SLR mirror assemblies are bulky, complex and costly.
Sony's SLT cameras look and function like DSLRs, but have a fixed, semitranslucent mirror that transmits most of the light to the image sensor while directing a small portion up to the phase-detection AF sensor in the top of the camera. Thus, you get full-time phase-detection AF in Live View and video modes. To provide an image for eye-level viewing, the SLT cameras employ an electronic viewfinder instead of an SLR's optical unit. This saves bulk, complexity and cost, and eliminates vibration due to mirror movement. An EVF also can display lots of useful shooting information and lets you zoom the image for easy manual focusing.
Early electronic viewfinders were pretty bad, providing low resolution and slow refresh rates, making them unsuitable for manual focusing and tracking action. The XGA OLED Tru-Finder electronic viewfinders in the Sony SLT-A77 and A65 (and the mirrorless NEX-7) pretty well resolve these problems. We were able to track birds in flight (and do video clips with full-time continuous phase-detection AF!) after a bit of practice with our A77 preproduction test camera.
These two examples of electronic viewfinders show some of the sophisticated electronics involved. EVFs are essentially tiny monitors. As their resolution and low-light performance improve, they will replace more and more optical viewfinders.