ZWO ASI130MM monochrome high frame rate camera

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ZWO ASI130MM monochrome high frame rate camera

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A quality camera for most purposes, but be careful with deep-sky imaging

The ASI130MM high frame rate camera from ZWO certainly looks striking thanks to its gold finish. Though primarily intended for Solar System imaging, it is also capable of taking pictures of brighter deep-sky objects.
Inside the camera is a monochrome 1.3 megapixel CMOS sensor; sensors of this type are easier to manufacture than true CCD sensors. Each pixel has a small active amplifier to boost the delicate signal it records, and for many years purist imagers steered away from CMOS, preferring the cleaner image quality of a pure CCD. However the technology has come on fast and CMOS cameras are now making good headway for low-cost astronomical imaging.
The ASI130MM is pretty quick to set up, a process that consists of downloading and installing the relevant drivers from the ZWO website. Links to various freeware control programs can also be found on this website. A single USB cable connects the camera to a computer.
Overcoming the seeing
The camera body natively fits into a 2-inch eyepiece holder, and a 1.25-inch adaptor is supplied. Being small and light, the camera certainly doesn’t strain the telescope or mount. We imaged the Sun, Moon, Jupiter and the wonderful Orion Nebula.
The big, bright Moon was perfectly suited for the ASI130MM: the capture quality was excellent, the camera recording some fantastic fine detail. The 30 frames per second (fps) limit at the largest frame size (1280x1024) was perfectly adequate to overcome the mediocre seeing conditions, producing some superb wide lunar vistas. Despite the seeing, we were especially impressed by a 640x480 capture of crater Petavius, with its large prominent rille running from its central mountain complex to the crater’s rim. The camera also recorded many fine cracks in Petavius’s floor.
The smaller pixel array settings allow capture rates to be bumped up, which is ideal for planets. Here we found the camera’s sensitivity to be a slight issue. With a peak quantum efficiency of 55 per cent at 560nm wavelength (yellow-green), we found ourselves reducing frame rates to get a decent signal. This was most evident comparing the ASI130MM with its predecessor, the ASI120MM, which has a peak quantum efficiency of 75 per cent (510nm/green) and is only slightly more expensive. 
Quantum efficiency expresses how good a chip is at converting incoming photons to a signal; the higher the value the better. At high gain, the ASI130MM’s noise levels also started to creep up resulting in some fixed pattern noise in processed images. Keep the gain off high though and the noise is acceptable. As long as you keep image scales to realistic values, the camera is fine for the brighter planets and we were able to get some decent results from Jupiter even with some quite wobbly seeing. 
Our final tests were on deep-sky objects. For bright and medium-bright objects such as the Orion Nebula, the ASI130MM provided adequate results. Noise was an issue, so creating matching dark frames proved to be essential. Through a 4-inch refractor, we were able to pull out some good detail in the nebula and the faint wisps of glowing gas that surround it. For someone starting out in deep-sky imaging, the camera will give a lot of enjoyment. The added advantage is that once you progress to a higher-end deep-sky camera, you can always use the ASI130MM for autoguiding.
This is a good all round camera. The level of detail achieved while imaging the Sun and Moon was excellent. The camera’s astonishing ability to capture full, 1280x1024 frames at 30fps really pays off for large extended objects and is arguably the ASI130MM’s biggest advantage. Keep the image scale modest and it’s also capable of delivering stunning planetary results too. It can even do deep-sky imaging, but being uncooled, noise levels do make careful calibration important.
A flexible friend

Whichever way you look at it, the ASI130MM is a very flexible camera able to satisfy many imaging needs. It’s great for Solar System imaging and the ability to select from 10 preset pixel array sizes – ranging from a full frame 1280x1024 down to 320x200 – gives you a lot of options. Larger frame sizes require the transfer of more data, so maximum frame rates are reduced, but 30fps for a 1280x1024 pixel array is still very respectable.

The larger sizes are great for covering big areas of the Sun or Moon in one go. Smaller sizes are better suited to planets, the reduced data overhead permitting an excellent 100fps in a typical planetary 640x480 mode. Longer, multi-second exposures permit deep-sky imaging. Using supporting software, the imaging chip can be binned to increase sensitivity at the expense of resolution. For example, four pixels can be ganged together to form a 2x2 ‘super-pixel’ (2x2 binning), with an array resolution of 640x512 pixels. Alternatively, 16 pixels (4x4 binning) produce an array size of 320x256. The binned modes are great for boosting sensitivity during autoguiding.

USB 2.0 - The ASI130MM connects to a computer via a decent length of supplied USB cable. The full size frame can be delivered to your computer at 30fps, pushing the USB 2.0 transfer rate to its limit. The camera also derives its power over this interface making it a great, high-quality, portable imaging solution.

ST-4 Guide Port - The ST-4 guide port on the side of the camera body allows the camera to be connected to a mount and – with appropriate software – used for autoguiding purposes. Various freeware packages can be used to control and monitor the autoguiding operation, including PHD Guiding.
Body - The ASI130MM is housed in a gold-coloured aluminium body. The front aperture is T2-threaded (M42x0.72) with an external diameter that fits a 2-inch eyepiece holder. A 1.25-inch adaptor is also provided. To the rear there is a standard ¼-20 tripod thread.
Sensor - The camera’s imaging magic happens courtesy of a MT9M001 CMOS sensor. This 0.5-inch chip (5:4 aspect ratio, 6.66x5.32mm) packs 1,310,720 active pixels into a 1280x1024 pixel imaging array. Smaller areas of the array can be defined to improve frame rates. The 5.2μm square pixels can also be binned for higher overall sensitivity.
Control Software and Drivers - ZWO provides drivers for all of its cameras on its website, but the job of controlling the camera is sensibly handed over to third-party programs such as SharpCap and FireCapture (pictured). ASCOM drivers for the camera and its ST-4 port can also be downloaded via the ZWO website.

This review originally appeared in the June 2014 issue of BBC Sky at Night Magazine. Prices correct at time of going to press.

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