Nikon D7200 key features
•24.2MP CMOS sensor with no optical low-pass filter
•Multi-CAM 3500DX II 51-point AF system, all sensitive to -3EV
•2,016-pixel RGB metering sensor, used for 3D subject tracking in AF-C
•ISO 100-25,600, with ISO 51,200 and 102,400 black and white modes
•6 fps continuous shooting (7 fps in 1.3x crop mode) with increased buffer depth
•1/8000 sec maximum shutter speed
•3.2", 1.2M dot RGBW LCD display
•1080/60p video (1.3x crop only) with clean output over HDMI and Flat Picture Control
•Dual SD card slots
•Wi-Fi with NFC
•Magnesium alloy weather-sealed body
One of the most important features on the D7200 is its improved AF system. Nikon has updated the D7200 to its Multi-CAM 3500DX II system, which still offers 51 AF points (the central 15 of which are cross-type), but now all of those points are sensitive to -3EV, while the D7100's were limited to -2EV.
The most obvious improvement in the D7200 compared to the D7100 will be noticed by anyone who shoots continuously. The buffer size on the D7100 was tiny and filled up almost instantly, which not only affected burst shooting but bracketing as well. You can now fire away with the D7200 for up to 18 14-bit lossless compressed, 27 12-bit compressed Raws, or 100+ JPEGs. The maximum burst rate remains the same: 6 fps at full size and 7 fps in 1.3x crop mode.
The D7200 can now extend its ISO higher than on its predecessor, but with a catch. Seeing how little color detail would be left at ISO 51,200 and 102,400, Nikon has chosen to make those two sensitivities black and white only.
Two other new features of note are 60p video (with Flat Picture Control, also available for stills) and Wi-Fi. While the addition of 60p video is nice, it's only available in 1.3x crop mode. The D7200 also has Wi-Fi with NFC, which Nikon has branded 'SnapBridge', which allows for remote camera control and image transfer.
As mentioned above, the D7200's new autofocus system is a big deal. You can focus in conditions a full stop dimmer, and the updated Multi-CAM 3500 II sensor in the D750 showed that it continued to focus in significantly darker conditions than the Multi-CAM 3500 sensor in the D810 (a DX variant of which was used in the D7100). What this means is that the camera will focus a whole lot better in low light conditions, across the entire frame. In other words, its non-central AF points will likely focus in dimmer conditions than any other DSLR out there, save for Nikon's own D750.
The refined autofocus system is a boon for photographers, particularly low-light ones. First of all, the AF area coverage is extremely wide, with AF points going out to the edge of the frame, no different from the D7100, in fact (which is a good thing). The real kicker with the D7200 is that all 51 points can focus down to -3EV just like the D750, which is the best of any DSLR in this class. By comparison, the D7100's points focused down to -2EV.
In tough lighting scenarios, when there's a lack of subject contrast (low light, or backlit situations), non-cross-type points can struggle. Under these situations, the more axes along which an AF point is 'looking' for detail, the more likely focus will be acquired. That's because it's much less likely that a subject lacks both vertical and horizontal contrast compared to lacking either or.
Something else we'd have loved to have seen in the D7200: a higher-resolution RGB metering sensor to enable more accurate subject tracking and face detection during through-the-viewfinder autofocus. The D750, D810, and D4S have remarkable subject (or '3D') tracking capabilities, where the camera uses its 91,000-pixel RGB metering sensor to 'see' and 'understand' the subject you're trying to focus on, and follow it by automatically selecting the appropriate AF point to stay on the (moving) subject.
The higher the resolution of the metering sensor, the more accurately the camera can do this, which is why Nikon's cameras with 91,000-pixel RGB sensors supersede the capabilities of their cameras with 2,016-pixel sensors. It's also why the D750 can find faces in OVF shooting, but the D7200 can't.
If you want to control your camera without laying a hand on it, then you'll appreciate the D7200's built-in Wi-Fi. Naturally, photos can be transferred and shared, which is extra-easy if you have a NFC-compatible smartphone.
Lastly, there's battery life. Perhaps its due to the more efficient EXPEED 4 processor, but whatever Nikon has done, it's managed to squeeze another 160 shots per charge out of the D7200 compared to the D7100.