Of course, there are pro jobs that require higher pixel counts. For those, rumor has it that both Canon and Nikon have higher-res (30+ MP) replacement models in the works for their "semipro" DSLRs. And, of course, there's always medium-format digital when really high pixel count matters. But for general pro DSLR needs, the new cameras' 16 to 18 megapixels seem to be the sweet spot where optimum resolution, speed and image quality intersect.
Canon and Nikon aren't the only manufacturers offering new DSLRs of interest to pro photographers, of course. The Sigma SD1 and Sony SLT-A77 are also pro-level tools. While Sony openly states that the A77 isn't a pro model, it features a 24.3-megapixel APS-C sensor, weatherproofing and 12 fps full-res shooting. The SD1 brings a pro build to Sigma's DSLR line, with triple the pixel count of its predecessors. Sigma DSLRs feature the unique Foveon image sensor, which, unlike conventional sensors, records color data for all three primary colors at every pixel site: the SD1 features 14.8 million pixel sites and, thus, 45 million pixels (in three stacked layers).
The D4 is Nikon's new flagship pro DSLR, replacing the 12.1-megapixel D3S low-light/action camera and possibly the 24.5-megapixel D3X.
Rugged, Sealed Body. Of course, the D4 is rugged and sealed against the elements like its predecessors. It features a 3.2-inch, 921K-dot LCD monitor that can automatically adjust to ambient light levels. More controls are provided for easier vertical-format shooting. Many buttons are illuminated, so you can find them in light levels requiring ISO 204,800.
HD Video. The D4 can do 1920x1080p full HD video at 30 and 24 fps, and 1280x720p HD at 60 fps. You can adjust the shutter speed, aperture and ISO independently. A built-in microphone provides mono sound; there are also jacks for an external stereo mic and headphones. B-frame compression makes for more detailed output with reasonable file size. The low-pass filter over the image sensor has been optimized to minimize video artifacts. You now can shoot video at three crop settings: FX (full-frame), DX (APS-C, 1.5x crop) and 2.7x crop. Since maximum video resolution is 1920x1080, there's no loss of resolution when you crop for movies as there is when you do it for stills. These modes provide lots of focal-length/framing flexibility with each of your lenses. If you have the 70-200mm ƒ/2.8, it effectively becomes a 105-300mm in DX mode and a 189-540mm in 2.7x mode—all at full HD resolution.
Shooting Speed. Featuring an all-new, Nikon-designed, 16.2-megapixel, full-frame CMOS sensor and EXPEED 3 image processing, the D4 can shoot full-resolution images, JPEG or NEF, at 10 fps with autofocusing and metering for each shot. It also can shoot full-res images at 11 fps with focus and exposure locked at the first frame. There's a new totally silent shutter release mode, in which the camera can shoot 2-megapixel images at 12 or 24 fps.
ISO 204,800. Normal ISO range is 100-12,800, expandable down to 50 and up to 204,800, with all settings available for both still and video shooting.
Dual Card Slots. There are two memory card slots, one for CompactFlash (UDMA 7-compliant) and one for the new XQD cards, which are 25% to 30% faster. The Virtual Horizon now covers roll, pitch and yaw axes.
All New Metering System. The D4's RGB 3D Color Matrix Metering III system also is all-new, with a 91,000-pixel RGB metering sensor (vs. 1005 pixels for the D3S).