Sky and Telescope - April 2016 - 61

Left: Due to the extremely low-noise characteristics of the Sony ICX814 CCD
detector, dark-frame calibration is virtually unnecessary. This image of M20
was captured with a 12½-inch f/4 Newtonian for a total exposure of 50 minutes, and was processed without dark-frame calibration. Only a few dozen hot
pixels can be seen in the ﬁnal result. Above: Included with the camera is the
manufacturer's control software SXV_HCOL_USB, which controls the primary
functions of the camera, autoguider, and ﬁlter wheel.

most straightforward and quickest setup time of any
deep-sky astrophotography conﬁguration I have used.
Even swapping the Trius-SX814C, Lodestar X2, and the
OAG between the small refractor and the Newtonian
meant little down time. I was into an imaging run in
record time. The sensitivity of the Lodestar X2 guider
was a big part of the quick setup, since the search for
suitable guide stars fast and easy.

Dark Calibration, or Not?
The low noise in the Trius-SX814C and the camera's
regulated, two-stage TEC cooling means that what
few hot pixels are produced in most exposures can be
removed using pixel-rejection algorithms when stacking
sub exposures. The hot pixels would also be mitigated
by dithering a number of exposures. (Dithering involves
moving the telescope slightly between exposures so that
spurious signal is averaged out when star images are
registered and combined into a single result.) Indeed,
the manual for the Trius-SX814C states that dark frames
subtracted from exposures of 10 minutes or less may in
fact increase noise in the ﬁnal image.
I shot a series of dark frames for my test exposures
with the camera, but I was still impressed by how little
noise was present in 5- and 10-minute exposures without
being processed with the dark frames. Furthermore, I
typically ran the camera temperature at -20°°C, though
the cooler can operate as much as 40°C below ambient
air temperature and further reduce thermal noise.

All in All
My takeaways from shooting with the Trius are an
appreciation for its ease of use and its smooth, low-noise
results. Veteran deep-sky astrophotographers know that
a single 5- or 10-minute exposure is only the beginning
of a picture; the "clean" look of each exposure taken with
the Trius-SX814C makes the ﬁnal result more rewarding. The camera was very sensitive for a chip with small
pixels and a Bayer ﬁlter matrix on the CCD array.
While the lack of a mechanical shutter in both the
Trius and Lodestar X2 cameras was never a problem for
me, it could be seen as a shortcoming for astrophotographers interested in remote imaging. Yet a partial solution is to put an opaque "ﬁ lter" one of the ﬁ lter wheel's
slots, which can then function as a mechanical shutter
for the main camera.
The trio comprising the Trius-SX814C, Mini Filter
Wheel with its OAG, and Lodestar X2 autoguider made
for an easy-to-use total package. The extremely low-noise
Sony detectors can eliminate a time-consuming process at the telescope, allowing you to record more light
images each night. Astrophotographers choosing any
one or a combination of these products will be rewarded
by a well-designed system that makes the road to highquality color deep-sky astrophotography much easier. ✦
North Carolina photojournalist Johnny Horne has taken
pictures for The Fayetteville Observer for 43 years and has
been imaging the night sky since age 12.
Sk yandTelescope.com April 2016

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Sky and Telescope - April 2016

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