Like the Pentax, the Nikon D800E is features an excellent build quality and is fully weather-sealed. It is very well-balanced and it feels great in your hands. It is easy to hold steadily with most non-tele lenses, including the 24-70mm. Lenses bearing the "VR" designation are stabilized, offering up to 4 stops of compensation, meaning that you can shoot with these lenses in sub-optimal lighting conditions.
Although Nikon doesn't do much to advertise it, most of their full-frame lenses are also weather sealed. Below is a complete list of weather-sealed Nikon FX lenses (both lenses used in this review are included):
When non-full-frame lenses are mounted on the D800E, the camera automatically enables DX mode, which produces 15.3-megapixel (4,800 x 3,200) files.
On the back of the D800E you'll find the iconic Nikon screen protector, which can be replaced or removed if needed.
The D800E's button layout isn't quite is intuitive as that of Pentax DSLRs (and we're not saying this simply because we're more familiar with Pentax cameras). There is quite a bit of redundancy in the buttons (i.e. having an OK button in addition to a center button on the 8-way pad), and it is often the case that two buttons need to be pressed at the same time in order to accomplish something. For example, to switch shooting modes, you have to hold the mode button and turn an e-dial at the same time, and the same applies when you go to switch AF modes. The thing we found most annoying is that changing ISO basically forces you to take your eye away from the viewfinder, as the operation requires you to use both hands (one to press the ISO button, and the other to turn the e-dial). Also, in playback mode, the Nikon doesn't allow you to use the e-dials to zoom in on the photo, meaning that again you have to use both hands (one to operate the 8-way pad and the other to press either of the zoom buttons on the left) when reviewing your photos. The 645D makes things much easier by mapping one e-dial to zooming and the other one for cycling through photos.
Unlike the 645D, the D800E lacks an interactive status screen, and generally only the external buttons can be used to change shooting settings. Thus, the D800E has more of a learning curve than the Pentax.
Despite these quirks, the D800E also has some very nice features, including two customizable buttons to the right of the lens mount. There is also a drive mode ring and a flash compensation button (on the Pentax, you have to press the buttons and look at the LCD at the same to time when changing either of these settings). Lastly, we'd like to mention that the D800E's memory card door is quite a bit bigger than that of the 645D, making it easier to open.
One feature that the D800E has that the 645D lacks is a viewfinder blind, which is enabled using the switch to the left of the eyepiece. There is also quite a large number of helpful tooltips (accessible via the question mark button), though Nikon hasn't taken this as far as on intro-level cameras. Finally, don't forget that the D800E has a built-in flash, which isn't something you'll always find on high-end DSLRs!
For the most part, all other buttons behave very similarly between the two cameras. Overall, we find the D800E to have fairly good handling, and due to its relatively small size, it can easily be used hand-held (though the best image quality is obviously obtained when using a tripod). If the D800E had Hyper Program mode, it would be much closer to being a perfect camera! We would have also liked it if some of the buttons were easier to reach while shooting. The D800E scores higher than the 645D in our Handling rating because of its versatility and smaller size, while the 645D scores higher in the User Interface rating due to its better button layout and more intuitive interface.
The optional Nikon MB-D12 battery grip makes it easier to shoot verticals with the D800E, and it also doubles the camera's battery life. It accepts either one additional EN-EL15 battery or 8 AA's, and is priced at $389.
Furthermore, with the battery grip the D800E can shoot at up to 6FPS, rather than the standard 4FPS, in DX mode.
Now, let's compare the two cameras side-by-side.