Sunday, March 6, 2011

Affordable CCD Cameras: Amateur Astronomy’s Weakest Link?

Given that quite a number of amateur astronomers now use “affordable” CCD cameras to capture what their telescope sees for posting on the web, does ultimate CCD camera performance still matters?


By: Ringo Bones


Once upon a time – or at least back in the 1970s and very early 1990s from my perspective – amateur astronomers used to rely on their handy film-based cameras with selectable exposure times to capture wonderful photos of what their home-based astronomy telescope set-up had seen. Then, digital Charged-Coupled Device cameras (CCD cameras) became low enough in retail price to pose serious competition to the humble film-based camera with selectable exposure times. As of late, given that CCD cameras capture what they “see” in digital form – as in format – quite a number of amateur astronomers had been busy posting / uploading what their astronomical telescope had seen on the web and / or their respective social network accounts – i.e. Facebook. But does the ultimate quality of your “affordable” CCD camera currently connected to you backyard telescope really matters?

The plain truth is, the quality of your imaging system – i.e. your backyard astronomical telescope and affordable CCD camera set-up – is fundamental to the quality of your results. Since the proliferation of back-illuminated grade one CCD cameras on the market aimed at amateur astronomers, the issue of quantum efficiency has more than ever became the selling point in the entry-level price point of CCD cameras for astronomical telescope use. But why is quantum efficiency so important by the way?

Quantum efficiency or QE is a measure of how much light gathered – typically by the front-end optics of your astronomical telescope – actually gets converted to charge in a typical CCD chip of a CCD camera. If your CCD camera has a rated peak QE of 85%, then it means that 85 out of every 100 photons striking the CCD get counted.

In practice, typical front-illuminated CCD cameras have a much lesser quantum efficiency than back-illuminated CCD cameras. Front-illuminated CCD cameras have a typical quantum efficiency of around 25% to 45%. And front-illuminated CCD cameras are also quite inefficient in the blue end of the visible spectrum where their quantum efficiency falls to a mere 5%, while a typical back-illuminated CCD camera only falls off to 70%.

During the latter half of the 1980s, mechanical sophistication – i.e. the expensive bits of your backyard astronomical telescope set up like optics and the related support systems – can already be replaced by relatively low-cost electronics, thus bringing enormous cost savings resulting in reduced exposure times brought about by a CCD camera with much higher quantum efficiency can be a boon for the amateur astronomer on a budget.

A shorter exposure time means lesser reliance on your astronomical telescope’s rather expensive mechanical systems – i.e. low-cost telescopes usually use low-cost mechanical systems. Better sensitivity via use of CCD cameras with higher QE means a smaller aperture can now accomplish what a larger – and pricier – telescope would before. Using a CCD camera with higher quantum efficiencies also allows you to image fainter objects in a shorter time, allowing you to image more objects per night using the backyard astronomy telescope set-up that you currently have. So buy the best-performing CCD camera for your astronomical telescope that you can comfortably afford to attain amateur astronomy bliss.

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