Sky and Telescope - February 2016 - 58

S&T Test Report
the D810a turns oﬀ all exposure indicators and lights.
Though helpful, this can make it a bit tricky to see where
you stand during an exposure.
The camera includes a helpful built-in intervalometer. This feature allows you to program the length and
number of exposures you'll take in a sequence without
needing an external device, as is usually required with
other cameras. The secret to using it is to set the interval
to the length of the exposure plus the length of time you
want in between exposures. And while you can't stop an
exposure once it's started without powering oﬀ the camera, you can stop the intervalometer when it is between
exposures by pressing the OK button.
The D810a oﬀers long-exposure noise reduction.
This is a common feature in which the camera takes an
additional exposure of the same length as the previous
image with the shutter closed, then subtracts that image
from the last to remove dark current that adds electronic
noise to an image. It's best to disable this function, as it
doubles the time needed for exposures and really isn't
necessary unless you are shooting at extremely high

Left: This enlargement shows hot pixels and color noise from a 30-minute exposure at ISO 200 at 65°°F ambient temperature. Right: The noise and splotches
are completely removed with the special astro noise-reduction function in Nikon
NX-D v1.2.1 image-processing software.

ambient temperatures. An alternative is to shoot these
dark frames later and subtract them from your images
manually with image-processing software.
One issue I had with the D810a was its lack of an
articulated LCD screen that you can adjust for convenient viewing when the camera is attached to your telescope. Though not a deal-breaker, it is a neck strainer,
especially if you are using a refractor or catadioptric
telescope pointed anywhere higher than about 15° above
the horizon - in other words, for most every astrophoto.
Like Nikon's other DSLR cameras, the D810a Lv mode
image defaults to a correct brightness display, no matter
what exposure the camera is set to. Users can enable
an exposure simulation option in Lv mode in which the
brightness of the display changes as you change the
exposure. Press the OK button on the back of the camera
while in Lv mode to enable this feature.
While shooting, be sure to save RAW images in 14-bit
NEF lossless ﬁ le format. The camera oﬀers many other
options such as a RAW Small format with one quarter
the pixel count. This may seem attractive but should be
avoided as it is not a true RAW ﬁ le, and it is not actual
pixel binning like that done in an astronomical CCD
camera - this setting simply down-samples your image
after the fact, rather than grouping pixels to make them
act as a larger, more light-sensitive pixel unit.
Unlike some other DSLR models with Lv mode, the
D810a isn't useful for high-resolution planetary imaging,
because the Lv mode video stream is heavily compressed.

Color Balance
Nikon states that the D810a is not recommended for
general daylight photography. But in practice, the camera
produces very good color for normal daytime subjects,
such as family snapshots.
Like most DSLRs, the camera's automatic white-balance settings produce inconsistent results with astronomical subjects. Choose "Direct Sunlight" or, better
yet, program your own custom white-balance settings to
get the best results when shooting nighttime targets.
Once you start shooting with the Nikon D810a, the
camera's extended Hα sensitivity immediately becomes
apparent. Even short exposures of 15 seconds or so
reveal the large, red nebulous regions in Cygnus with
untracked shots using the AF-S Nikkor 14-24mm f/2.8G
ED lens supplied with our test camera for this review.

Nightscapes and Time-Lapse Imaging

The D810a reveals its great color performance on nebulae in this roughly 1½-hour
photo of the Veil Nebula in Cygnus. The author captured the shot through an
Astro-Physics 130EDFGT refractor working at f/4.7, and the individual images
were aligned and stacked using ImagesPlus.

Februar y 2016 sky & telescope

As mentioned earlier, the D810a has a number of features that are extremely useful for astrophotographers,
particularly those who specialize in "nightscape" photography. In addition to the built-in intervalometer, the
camera includes an electronic "virtual horizon" feature
that helps you quickly level your camera and the subject
in the picture frame. The intervalometer allows for ﬁ xed-

Sky and Telescope - February 2016

Table of Contents for the Digital Edition of Sky and Telescope - February 2016