Nikon D810A DSLR is is a modified version of the D810 optimized for astrophotography and other scientific applications.
The infrared (IR) cut filter has been modified to allow transmission of the hydrogen alpha spectral line, resulting in four times greater sensitivity of the 656nm wavelength. This enables astrophotography with clear reproduction of the vivid reds emitted by nebulae and galaxies.
A new Long Exposure M Mode that giving users the ability to set shutter speeds from from 4 to 900 sec (15 minutes), as well as Bulb and Time settings.
A Virtual Exposure Preview Mode makes focusing and composing images easier, which displays an estimated preview image and is available when shooting at shutter speeds longer than 30 seconds when in Live View. The brightened preview image represents a 30 second exposure, simplifying focusing and composition.