Supplier: 365 Astronomy
Telephone: 020 3384 5187
Having firmly established itself in the market for planetary cameras, Chinese firm ZWO has more recently turned its attention to the demanding area of deep-sky imaging.
The ASI071MC-Cool is a one-shot colour camera with electronic cooling capability, making it possible to capture long exposure photographs without unwanted noise artefacts.
This camera has a Sony IMX071 CMOS sensor that captures colour photographs, so we matched it with an apochromatic refractor with a large flat field that could test the entire chip.
Barrel shaped, the camera screws onto a telescope or an accessory via an M42 thread and attaches to a computer laptop via a USB 3.0 cable.
The supplied mini CD contains drivers and software to operate the camera, and most third-party astrophotography applications support ZWO cameras.
An easy-to-follow Quick Start Guide had our review camera set up and ready to go in just a few minutes.
To activate the cooling and to use the USB hub, you need a 12V DC, 3A power supply – not included with the camera.
The camera’s fan is virtually silent and quickly cooled the ASI071MC to –20°C, a good 35°C cooler than the ambient temperature.
However, we did note that quickly dropping the temperature resulted in a patchy image, caused by residual moisture within the sensor chamber freezing on the chip.
Eventually we settled on a working temperature of –5°C for all our photographs.
This efficiently eliminated any problems with electronic noise and amp glow, but maintained an easy-to-reproduce imaging temperature at any time of year for most climates.
We also added a 2-inch infrared/ultraviolet-cut filter as the camera window does not block these wavelengths.
Although eminently suited to deep-sky astrophotography, the ASI071MC-Cool also performs solidly as a planetary or lunar camera.
High frame rates are achievable by reducing the size of the captured image, and we easily achieved the maximum frame rate of 134 frames per second (fps) when imaging at 320×240 pixels.
Even in USB 2.0 mode we recorded frame rates of 56fps at 800×600 pixels, although the USB 3.0 connection is preferable as it enables faster downloads of larger images.
Debate continues over the relative merits of monochrome cameras versus their colour counterparts, but the fact remains that one-shot colour devices such as the ASI071MC-Cool allow true-colour photographs to be captured without the additional expense of a filter wheel and filters, and with considerably less time spent in processing the resulting images.
The images we captured were taken under average suburban skies, and calibrated and stacked in the freeware program DeepSkyStacker.
To finish, they were were each given basic adjustments – taking just a few minutes – using editing software.
This ability to efficiently make the most of the limited clear skies that many experience makes colour cameras very appealing, and as a substantial financial investment it is worth considering typical sky conditions and available free time for image capturing and processing.
We were impressed with the quality of the pictures the ASI071MC-Cool produced after calibration and stacking.
With an average exposure time of 10 minutes for each frame, we were able to capture images with natural star colours, and the excellent sensitivity of the sensor revealed faint objects without bloating brighter ones.
In our image of the beautiful edge-on galaxy NGC 891 in Andromeda, the ASI071MC-Cool also captured dozens of other galaxies at vast distances.
Subtle colour was revealed in NGC 7331, which was nicely drawn out, along with the nearby Stephan’s Quintet in the same field of view, while images of the Triangulum Galaxy, M33, revealed well-defined hydrogen emission areas.
The red and hydrogen-alpha wavelength sensitivity of the camera is very good.
We consider that the ASI071MC-Cool has to be a contender for anybody seeking a camera that will enable them to take print-quality photographs, with little other equipment and a minimum of image processing experience.
Outstanding feature: A sublime sensor
The heart of the camera is the renowned Sony IMX071 CMOS sensor, an APS-C chip used in some of the most popular DSLR cameras.
It boasts a 14-bit, 4,944×3,284-pixel array, yielding 16MB photographs with an excellent signal to noise ratio and high sensitivity.
This large chip, 28.4mm across the diagonal, allows you to capture large swathes of the sky and is perfect for imaging extensive nebulae and galaxies insofar as your own telescope allows.
Although unfavourably placed, we spent time imaging the Eagle Nebula, M16 in Serpens.
The resulting image demonstrated that the chip is able to bring home the deep-red hydrogen emission regions of a nebula, which is important for both revealing the extent of deep-sky objects and delivering a good overall colour balance.
Using a 6nm hydrogen-alpha filter with the camera resulted in a decent response to the faint hydrogen signal, and would allow the camera to be used for narrowband imaging too with a little persistence.
This capable sensor makes the ASI071MC-Cool a very attractive deep-sky camera.
Protecting the delicate CMOS sensor is a 2mm anti-reflection window.
Cooling the camera chip also cools this window, which could attract condensation, especially with open tube telescopes such as reflectors.
To alleviate this issue the window has a heating element that can be controlled in software such as SharpCap – which is included on the CD.
USB 2.0 hub
Cable management on an astrophotography rig can be a real problem.
The USB 2.0 hub included on the rear of the camera allows shorter cables to be directly attached to your other accessories instead of them all linking individually to your computer – cutting down on issues arising from a web of long, trailing cables.
Tilt-adjustable front plate
The front of the camera is a collimating plate with three push-pull screws for adjustment.
The idea is that any tilt in the image can be offset this way, improving star shapes in the corners of the picture, for those who find they have issues with alignment.
The CMOS sensor chamber is sealed against moisture and there are desiccant tablets inside it.
If these eventually become ineffective an additional tablet holder can be attached by removing a screw in the camera body and simply screwing the extra chamber into place.
A packet of spare tablets is supplied.
The camera is supplied with two spacing adaptors (21mm and 16.5mm) a 1.25-inch nosepiece, an M42 to M48 conversion ring, two short USB 2.0 cables, a long USB 3.0 cable and a CD of the necessary drivers and software.
A fully padded zip bag protects the camera when not in use.
This review originally appeared in the November 2017 issue of BBC Sky at Night Magazine