http://www.skyandtelescope.com.au 71meant 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 is 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,Itypicallyranthecameratemperature
at -20°C,thoughthecoolercanoperateasmuchas
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 ‘filter’ in one of
the filter 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, enabling you to record more
light images each night. Astrophotographers choosing
any one or a combination of these products will be
rewarded with a well-designed system that makes the
road to high-quality, colour, deep sky astrophotography
much easier. ✦Photojournalist Johnny Horne has been taking pictures for
43 years and has been imaging the night sky since age 12.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 32-cm 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. Above: The manufacturer’s control software, SXV_HCOL_USB, controls the
primary functions of the camera, autoguider and filter wheel.