Sky & Telescope - June 2019 - 72

S&T Test Report

bytes for a 30-second clip made with
a small region of interest. The manual
does warn about this, but it was still an
eye opener to ﬁll more than 50 gigabytes of disk space recording about a
dozen video clips my ﬁrst night out.
These videos were later processed with
third-party software including RegiStax
and the freeware AutoStakkert!3.

On to the Deep Sky
Once the Moon was out of the evening sky it was time to try the DSI-IV
for deep-sky imaging. It's here where
I found room for improvement with
SkyCapture that I hadn't noticed when
shooting still images during my bench
testing in a relatively bright environment. For example, when framing faint
deep-sky targets, I usually make short
exposures of 20 to 60 seconds and
stretch them to extremes to see what's
in the ﬁeld. With SkyCapture, the image
that appears at the end of each exposure can't be stretched on screen as is.
You can examine a histogram of the
displayed image and make adjustments
to set the black and white points for
displaying a stretched image, but these
settings do not take effect until you
make the next exposure.
q During his testing, the author exclusively
used the SkyCapture software supplied with
the DSI-IV for his astronomical imaging. As
explained in the accompanying text, he feels
the software's long-exposure mode could
stand some improvement but was still effective
for capturing images. The screen grab seen
here displays one of the 10-minute exposures
used for the image above and was made while
the camera was in the process of running the
automated exposure sequence.

J U N E 2 019 * SK Y & TELESCOPE

p Switching the DSI-IV from shooting astronomical videos to making long exposures of deep-sky
objects involves only a few mouse clicks with the camera's included Meade SkyCapture software
and, for optimum results, connecting the 12-volt power supply for the cooling system. These
views of the Cone Nebula and Christmas Tree Cluster in Monoceros (left) and Horsehead Nebula
in Orion (right) were each assembled from fifteen 10-minute exposures through a hydrogen-alpha
filter with an 8-inch f/3 telescope.

The best workaround, apart from
making multiple exposures or guessing
at the correct histogram settings before
shooting the ﬁrst one (something that
is possible with experience), is to ﬁrst
save the image and then re-open it with
SkyCapture and use the Range function
in the Process menu to actively stretch
the image on screen. It's a bit clumsy,
not to mention time-consuming, especially if you're typing ﬁle names and the
like in the dark with gloves on.
There were also features of the
software that I couldn't get to work,
including the automatic functions for
dark-frame subtraction and ﬂat-ﬁeld
correction. These issues may be unique
to the DSI-IV update of the software,
since I noticed that the
ﬂat-ﬁeld function isn't
even discussed in the
older user's manual
that I mentioned earlier. Regardless, I don't
like using automatic
calibration routines
during image capture,
since I prefer having
unmodiﬁed raw data
that can be processed
later with various
calibration methods. As

such, I simply made standard dark and
ﬂat-ﬁeld exposures with the DSI-IV and
processed my light frames with thirdparty software.
Despite my nit-picks with SkyCapture, I did use the software exclusively
for all the imaging I did with the
DSI-IV, and I'm happy with my results.
Indeed, most astronomical cameras
come with only the most rudimentary
image-capture software (and some don't
come with any), so getting a package as
decent as SkyCapture included with the
purchase of the DSI-IV is really a plus.
In the end I found the DSI-IV to
be a very versatile camera that can
satisfy the needs of many of today's
astroimagers. It's a camera that can
shoot excellent astronomical video and
seamlessly transition to shooting decent
long-exposure deep-sky images. It can't
quite match the deep-sky performance
of a cooled, 16-bit, astronomical CCD
camera, but the DSI-IV is still a big step
up from the astrophotography that can
be done with DSLRs. And it comes with
a very attractive price tag, especially
given the software that's included.
■ DENNIS DI CICCO has been reviewing
astronomical equipment in the pages of
Sky & Telescope for more than 45 years.

Sky & Telescope - June 2019

Table of Contents for the Digital Edition of Sky & Telescope - June 2019