Sky & Telescope - April 2019 - 63

phy, Sony cameras are compatible with
many motion-control devices and bulbramping intervalometers. However, for
deep-sky imaging many imagers like to
use a laptop with specialized camera
control software to run their DSLRs.
Unfortunately, Sony users are out of
luck, as none of the popular control
programs (AstroPhotography Tool,
ImagesPlus, MaxIm DL, Nebulosity, or
PRISM) support Sony cameras.
To run the Sony at the telescope I
used a simple $50 Vello intervalometer
that connects to the α7 III through its
micro USB port to control the shutter.
It's what I also use to shoot simple timelapses with the Sony because, unlike all
current Canon and Nikon DSLRs, the
α7 III lacks a built-in intervalometer.

File Compatibility
For all testing I set the Sony to shoot
in uncompressed RAW mode, producing ﬁles 49 megabytes in size. However,
the issue with raw ﬁles from DSLRs and
mirrorless cameras is that no two cameras' ﬁles are alike. Software companies
update their raw developers several
times a year to open and decode ﬁles
from new cameras.
The mainstream raw developers all
opened and decoded the α7 III's ARW
raw ﬁles ﬁne, with one issue.

pu The Sony mirrorless cameras excel at
low-light videography and in formats up to
UltraHD or 4K, which the α7 III can shoot at
24 or 30 frames per second and at either 60 or
100 megabits per second. This is a still frame
from a 4K aurora movie captured at 24 fps/100
Mbps and at ISO 25,600 using the Venus Optics 15-mm lens at f/2.

Among specialized astronomy
programs I could test, Nebulosity 4.2
decoded Sony's raw ﬁ les, but DeepSkyStacker 4.1.1 could not, as it uses the
obsolete "dcraw" decoding module.
AstroPixelProcessor 1.07 can't open
Sony ARW ﬁ les at all. PixInsight 1.8.6
did open and decode the α7 III's ﬁ les
ﬁ ne using the new RAW support
module, which replaces the obsolete
DSLR_RAW module that shipped with
older versions of the program. Make
sure the module is replaced when you
update the program.

q Left: Control options for Sony cameras are limited. An external intervalometer such as this Vello
unit connects to the camera through its micro USB port (arrowed) to operate just the shutter for
time-lapses and deep-sky images with the camera on Bulb mode. Right: Due to a mirrorless camera's thinner body, attaching it to a telescope with a field flattener will usually require an additional
adapter to supply the correct lens-to-sensor distance. This is a Metabones adapter between the
Sony and a Hotech flattener equipped with a Canon T-ring.

Stars or Noise
Astrophotographers have criticized
Sony's mirrorless cameras for a ﬁrmware "improvement" the manufacturer
introduced in 2017 that eradicated faint
stars in raw ﬁles. This was an unwanted
side effect of noise smoothing applied
internally to exposures longer than 4
seconds. Such behavior would be unacceptable for serious astrophotography.
I found the Sony α7 III does not suffer from "star eating." In images taken
of the same targets with the Sony and
with the Canon 6D MkII and Nikon
D750, cameras that have never been
accused of eating stars, the Sony showed
stars to the same limiting magnitude
and just as sharply. The "star eater"
effect was simply not an issue. Other
artifacts were more serious.

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Sky & Telescope - April 2019

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