Colour CCD camera

A great CCD for DSLR users who want to upgrade but still keep it simple

WORDS: STEVE RICHARDS

The arrival of the Atik 4120EX CCD camera may raise an eyebrow from some deep-sky astrophotographers, as a little unusually only a colour version is available, with no monochrome alternative.

Mono CCDs require a set of three external colour filters and three different sets of exposures to produce a colour image. A luminance channel captured using a plain filter normally supplements these three colour ‘channels’. Colour CCDs, however, have a matrix of colour filters sublimated on the sensor’s surface, allowing them to capture all three colours in a single ‘shot’.

Mono CCD cameras are more popular as they produce slightly higher definition images and allow the use of narrowband filters to capture specific wavelengths of light without the impediment of the built-in filters. However, when clear skies are at a premium, colour CCD cameras have a big advantage of being able to capture a usable full colour image in a short period of time, making good use of short, cloud-free spells.

The appearance of the 4120EX follows Atik’s usual style, comprising a cleanly designed and beautifully executed electric red anodised aluminium cylinder with satin black trim. The accessories include a 1.25-inch nosepiece, 12V cigar lighter power cable, USB cable, a The new ATIK 4120EX is a bit of a departure from ATIK’s most popular cameras as it is equipped with a Sony ICX834AQG CCD sensor, which is only available as a colour variant. The sensor has a repeating matrix of red, green and blue filters on its surface, so light is filtered before it falls on the individual photosites that make up the sensor.

Downloaded images appear to be in mono, but the colour information is encoded into what is known as a Bayer Matrix that can be decoded later, using software, by a process known as de-Bayering. This process extracts the colour data from the mono image and uses a certain amount of interpolation to construct the final colour image. This method is exactly the same as that in a DSLR camera, although a DSLR has a built-in processor to carry out the de-Bayering.

The sensor is a very generous 13.2x8.8mm in size comprising 3.1µm pixels in an array measuring 4,242x2,830 pixels. This produces high-resolution images, making this camera a good choice for wide-field imaging. software CD, a multi-product user guide a small tool that allows you to remove the circular plug on the side of the sensor chamber for desiccant replenishment. The complete kit is supplied in a printed retail box.

The software CD includes drivers for AstroArt, CCDSoft, MaxIm DL and the universal standard ASCOM platform. Also included on it are Atik’s popular Artemis (image capture) and Dawn (image processing) programs, along with some short videos showing you how to use them. We elected to use the ASCOM driver as this allowed us to test the camera for general compatibility. Both the installation and software integration with our own MaxIm DL image capture software were quick and easy on our desktop computer running Windows XP.

Critical cooling

The camera has set-point cooling, which allows you to set a sensor cooling temperature (known as ‘delta T’) to as low as 25°C below the ambient temperature. Part of our testing took place in early September and on a couple of warm nights, we were unable to achieve cooling temperatures lower than –9°C (a delta T of –27°C). This could be an issue for some users during the summer months, but we were happy with the low-noise results