When comparing Nikon D5 vs Pentax K-1, the Slant community recommends Nikon D5 for most people. In the question“What are the best full frame DSLR cameras?” Nikon D5 is ranked 2nd while Pentax K-1 is ranked 3rd. The most important reason people chose Nikon D5 is:
D5 has 153 AF points of which you can select 55. 99 AF points are cross-type (of which 35 are selectable). 15 AF points work with f/8 lenses (of which 9 are selectable). The autofocus works down to LV -4. Autofocus is amazingly fast at 14 frames per second with top of the class accuracy (in tests performed by Tony Northrup it was only second to 1DX Mark II in terms of how many shots were in focus having just 6% fewer of shots be in focus).
Ranked in these QuestionsQuestion Ranking
Pro Advanced autofocus
D5 has 153 AF points of which you can select 55. 99 AF points are cross-type (of which 35 are selectable). 15 AF points work with f/8 lenses (of which 9 are selectable). The autofocus works down to LV -4.
Autofocus is amazingly fast at 14 frames per second with top of the class accuracy (in tests performed by Tony Northrup it was only second to 1DX Mark II in terms of how many shots were in focus having just 6% fewer of shots be in focus).
Pro Huge ISO range
D5 has a native ISO range of 100 to 102,400 which can be expanded from 50 to 3,280,000.
Pro Can automatically detect faces and focus on them
Pro Can shoot stills during video
Pro Great high ISO imaging capabilities
Pro Can take super low noise, high sharpness images with Pixel Shift Resolution enabled
K1 has an alternate shooting mode that can significantly reduce noise and increase sharpness. It's called Pixel Shift Resolution. Once enabled it will take 4 shots moving the sensor by 1 pixel each time in order to capture all color information for each pixel instead of distributing it over 4. A visualization can be found here.
Pixel Shift Resolution shooting mode takes longer as it's taking 4 shots instead of one and requires a couple of seconds after the shots have been taken to process the images into one so it won't work for sports or action, but it's great for landscape photography.
Pro In-body image stabilization allows stabilizing fast prime lenses
You can potentially do night photography without a tripod by using a fast prime lens wide open with in-body image stabilization.
Pro Great interface
Pro Good dynamic range
Pro LCD can be pulled out of the cradle
K-1 has a cross-tilt LCD.
Pro The K-1 + one of the Pentax Limited full-frame, all mechanical lenses is the dominant design in photography
It's not the camera alone; it's the camera and the lens together. Pentax's best lenses are the FA31/FA43/FA77 Limited series. There is no other camera + lens combination that can compete with the K-1 + one of the FA Limited lenses on a price/performance basis. It is not even a close competition.
Pro Built-in GPS
Great searching through picture libraries by location.
Pro Manual sensor shift allows taking tilt-shift photos with any lens
Pro Has LEDs that illuminate key parts of the camera
There's an LED that shines light on rear controls, there's another one that illuminates the lens mount, and an LED that highlights the card bay and remote release port. These can be really helpful in the dark.
Pro Automatically fixes horizontal level
Con Image quality is surpassed by much cheaper cameras
Nikon puts D5's AF capabilities above everything else to the point where cameras that cost less than half the price (like Nikon's own D810) have clearer, sharper images with higher dynamic range and higher resolution.
It's an extremely specialized camera. Unless you're doing photography that involves fast moving targets, the camera's capabilities will not justify the price.
Con Internal 4K video capture is limited to 3 minutes
Fortunately video can be sent over HDMI to an external recorder.
Con Dynamic range of base ISO could be better
According to tests performed by DxOMark, dynamic range of the D5 is at ~9.35 stops for base ISO (50 to 100). Lowest of any FF Nikon DSLR.
Con 4K video has a 1.3x crop
Con AF in video mode is lousy
Con Lacks built-in Wi-Fi
Con AF point coverage could be better
Con Low resolution for a flagship
The camera is 20MP, D810, for example is 36.3 MP.
Con Not all AF points can be manually selected
Out of the 153 AF points only 55 can be selected.
Con Autofocus could be better
Autofocus won't be able to consistently keep up with fast-moving subjects so it's not the best camera for action or sports. Additionally, it only has 33 AF points which by today's standards is on the lower side of things and they're not spread around as much as in other cameras.
Con Video capabilities could be better
It's reasonable to expect more than 1080p30 in a 2016 flagship camera.
Con Limited lineup of full-frame lenses
While Pentax has among the best selection of lenses created for APS-C sensors, this is their first full-frame camera and there aren't that many of them.