A full-frame, cooled camera that will appeal to dedicated astro imagers

WORDS: TIM JARDINE

VITAL STATS

• Price £3,850

• Sensor Sony IMX455, full-frame CMOS

• Resolution 61MP, 9,568 x 6,380

• Exposure range 0.1 milliseconds to 3,600 seconds

• Accessories 12V power supply, M54 nosepiece, M48 adaptor ring

• Size 102mm x 91mm

• Weight 710g

• Supplier Altair Astro

• Tel 01263 731505

• www.altairastro.com

The Hypercam AA61CFX is a full-frame, one-shot colour astronomy camera with 16-bit capability. Designed for serious astrophotography and dedicated enthusiasts, the AA61CFX represents a significant investment. Matching its high-end capabilities to the rest of an imaging setup is a crucial exercise, as this camera will quickly reveal any shortcomings in the equipment it’s used with. For our tests we selected a high-grade mount on a permanent pier and a 150mm apochromatic telescope, which provided a large enough colour-corrected, flat imaging field.

Accommodating the large sensor at the heart of the AA61CFX requires a stocky camera body, which is the familiar barrel-shape design. The front of the camera comes with an M54 x 0.75mm female thread, which gives plenty of unobstructed room around the edge of the sensor. Being a one-shot colour camera there is no need for additional filters, as the sensor’s optical window has built-in ultraviolet and infrared blocking, but additional specific band filters can be used if they are large enough for the sensor.

The camera is USB 3.0, which means that – with the size of the files being produced –a fast, reliable connection and computer are vital. This effectively restricts the length of the USB cable to 2m. Once we had installed the AltairCapture software, we attached the camera, using the supplied 1.5m USB cable, and it was recognised immediately. We then set about adjusting both the cooling system and the optical window heating settings. Although it is tempting to go as low as possible, we chose a sensible –10°C as a target that should be repeatable throughout much of the year in the UK. After a couple of minutes, the camera reached the desired temperature, and held it pretty steadily.

Keeping moisture down

While the sensor itself is being cooled, the front window can be heated as desired, which helps keep the outer face of it clear from dew or frost on humid nights. The sensor chamber itself is sealed and guaranteed to stay frost-free for two years, and we certainly had no issues with dew or frost while using the camera. Our review camera did have an issue with a dust mote, seemingly behind the optical window, which couldn’t be wiped off. It was invisible to the eye, however, and the flat frames removed the shadow from the images.

When comparing astronomy cameras it can be useful to compare the technical specifications, and these are listed as >90 per cent quantum efficiency, which is a measurement related to the sensitivity of the sensor to light, while a full well-depth of 110.4Ke is available in ‘LCG’ (low conversion gain) mode, and 50.8Ke using ‘HCG’ (high conversion gain).

The longest individual exposures we took were 15 minutes long, and the resulting images contained no traces of any unwanted electronic artefacts, sometimes called amp glow. Indeed, the quality of each exposure was exceptional and low in noise (unwanted artefacts), and once stacked together the integrated images were very high quality. We used the ‘HCG’ mode as recommended by the vendor, but there is also an ‘Ultra Low Read Noise’ option, and an 8-bit mode if desired.

Taking the vendor’s advice, we chose the ‘HCG’ (high conversion gain) setting in AltairCapture, using a gain setting of ‘1’ for the majority of our images. This gives the 16-bit camera the opportunity to make the most of its huge dynamic range, and brought to mind all the good things from imaging with older CCD cameras, including high sensitivity, high dynamic range and low noise (unwanted artefacts). In fact, the noise is so well controlled in this camera that even single exposures produced quite acceptable images. But, as is usual with CMOS cameras, we found that carefully selected calibration files improved our captures even further.

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Deep-sky testing

For targets we selected demanding objects like the Pleiades, M45, and the Orion Nebula, M42, which both contain some of the brightest and faintest elements in close proximity to each other; along with wider views of galaxy groups like the M81 and M82 pair, and the Rosette Nebula. The images revealed that the AA61CFX can handle bright stars and nebulosity admirably, and it allows the smaller stars and very faint, distant galaxies to shine too. We wish we could have tested the camera for longer, to attempt a really deep-sky capture of a galaxy chain or cluster. This would give the camera’s low-noise performance a chance to come into its own and reveal a wealth of small galaxies and objects that are normally obscured in the background.

We were able, however, to try turning up the gain and taking shorter images, for comparison. Here the AA61CFX showed that sacrificing a little range can still produce excellent images in a fraction of the time.

Overall, with its huge image area, low noise and high range performance, the Hypercam AA61CFX should satisfy the needs of even the most demanding astrophotographer.

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Software

AltairCapture software is included with the camera. It allows full control of all the camera settings – including heating and cooling, ‘HCG’ (High Conversion Gain), ‘LCG’ (Low Conversion Gain) and ‘Ultra Low Read Noise’ modes, region of interest imaging and real-time live focusing – all in a simple-to-learn, intuitive interface that keeps any distracting complications to a minimum.

KIT TO ADD

1. Altair Dual-Band 7nm Nebula Filter

2. Altair 150EDF APO Refractor

3. Altair PlanoStar 0.8x Reducer

VERDICT

THESHED/PHOTOSTUDIO , TIM JARDINE,