identical to that of Nikon’s popular
D750, a favorite DSLR camera of mine
for astrophotography. Pixels in both
cameras are 5.9 microns square, provid-
ing a good balance of noise vs. resolu-
tion. However, the sensor in the Z6 is
a new back-illuminated CMOS design,
which, along with Nikon’s latest Expeed
6 fi rmware, promises to yield lower noise
than the four-year-old D750.
I selected the Z6 for testing over
Nikon’s more expensive Z7 mirrorless
because the latter model, while provid-
ing higher resolution with 46 megapix-
els, will inevitably exhibit higher noise
due to its smaller 4.3-micron pixels.
For my testing, I shot with the Nikon
Z6 alongside both the D750 and the
Sony α7 III, to compare noise levels,
live view modes, movie capability, and
battery life.
Noise Levels
Key to performance for astrophotogra-
phy is how well cameras perform at the
high ISO speeds we typically employ for
most nightscape and deep-sky images.
In side-by-side tests of a sample night-
scape scene (my rural backyard) on
both moonless and moonlit nights, the
Z6 exhibited nearly identical noise lev-
els at ISO 3200 to 12,800 as the veteran
D750, seen below.
Luminance (overall grittiness) and
chrominance (color speckling) noise
levels looked very similar, with Z6
images appearing a bit lower in noise,
especially at ISO 12,800, but certainly
not by as much as even a half-stop
improvement. Comparing it to the Sony
α7 III also revealed nearly identical
high-ISO noise performance. All three
cameras were excellent, with no clear
winner in still images.
The Z6 sensor employs a signal path
design that is “ISO invariant.” The ben-
efi t is that a nightscape image shot at a
low ISO speed and therefore underex-
posed, then boosted later in exposure at
the computer should look nearly identi-
cal to a properly exposed image shot at a
high ISO speed to begin with.
ISO invariant sensors allow you to
increase shadow details in nightscape
foregrounds during processing without
introducing ugly artifacts such as exces-
sive noise, fi xed-pattern banding, and
magenta casts. A test dark-sky nightscapeshot at ISO 100, and so underexposed by
a full fi ve stops, did exhibit more random
colored pixels when boosted later in
processing, but overall it looked similar
to a properly exposed image. I did not
see any of the banding artifacts reported
by other Z6 reviewers when shadows are
boosted by extreme amounts.
The Nikon Z6 provides as low a noise
level as you’ll fi nd in a 24-megapixel
camera, with larger pixels and good
ISO invariant performance. Both traits
make the Z6 excellent for nightscape
and time-lapse photography.skyandtelescope.com • AUGUST 2019 69pAt the ISO 3200 to 12,800 speeds commonly used for nightscape images, the Nikon Z6 showed similar noise levels as the Sony α7 III and Nikon
D750, with the latter older camera marginally worse for noise at the highest ISO setting.
pNightscape images underexposed by as much as 5 EV by shooting at slow ISO speeds then
boosted later in processing looked similar to well-exposed images shot at a high ISO at the cam-
era. This demonstrates the Z6’s good “ISO invariant” sensor design, which is similar in perfor-
mance to that of the D750 and Sony α7 III.uThe Z6 can provide a very bright Live View
image by switching to its Movie Mode using
the dedicated lever at top, with the ISO set to
Hi1 or Hi2. This is a scene lit only by moonlight.Nikon Z6
ISO 3200Sony α7 III
ISO 3200Sony α7 III
ISO 3200
0 EVSony α7 III
ISO 100
–5 EVNikon D750
ISO 3200Nikon D750
ISO 3200
0 EVNikon D750
ISO 100
–5 EVNikon Z6
ISO 6400Sony α7 III
ISO 6400Nikon D750
ISO 6400Nikon Z6
ISO 12,800Nikon Z6
ISO 3200
0 EVNikon Z6
ISO 100
–5 EVSony α7 III
ISO 12,800Nikon D750
ISO 12,800