Using a cheap B/W CCD camera for astronomy

By Jenny Bailey

Last updated 23/10/00 19:42:05

Overview

There are a number of astronomy CCDs on the market costing over £600, I thought that it would be nice to see what was possible using a cheap ex-security camera CCD ( costing about £30 ).

The same principle can be applied using a webcam with direct connection onto the PC parallel port or USB port.

Mounting on the telescope

I am not an expert on telescope optics, so I bought a book 'Telescopes and Techniques' and decided that the CCD should completely replace the eyepiece. The CCD camera is equipped with its own lens, and this needs to be removed before it is attached to the telescope.

In order to mount the CCD camera on the back of the telescope, I purchased a 'T' adaptor for my telescope from our local astronomy suppliers - Green-Witch.

I mounted the camera on the back of the T adapter using insulation tape because I could not find any gaffer tape :-)

CCD Camera Parts

I must have purchased the CCD camera in about 1997 and it probably has a sensitivity of 2 lux. Newer security CCD cameras are capable of 0.2 lux.

I connected the camera to a UHF video modulator ( for a later project - put the camera on a kite ) and connected the UHF output to a winTV USB module connected to my laptop. The winTV software allowed me to capture images.

Here is the assembled unit ready for the back of the telescope

Picture of assembled CCD

Results

The focus seems to be a long way from the optical focus, you would not want to go between the two regularly.

With no eyepiece, it is not possible to change the magnification

The CCD seems to cope very badly with bright objects, its AGC does not seem to have too much dynamic range

Here is a picture of Saturn, probably the best result so far

picture of saturn

Here is a very poor image of Jupiter, you can ( almost ) see the moons at about three o'clock. Note that the colours ( grey scale ) have bleached out

bad picute of jupiter

Here is another bad picture of Jupiter with less video gain, you can see some banding

dark picture of Jupiter

Conclusion

Well, this wasn't a total waste of time, I find looking at a laptop screen much easier on the eye than looking through an eyepiece. You could argue that I therefore can't be a proper astronomer. I'm not.

A CCD designed for astronomical observations will have the following enhancements :

Better sensitivity

More dynamic range because of more bits in the A/D converter

Longer exposure times - a security camera is designed to follow moving images and therefore has shutter speeds of 20ms.

There seem to be a couple of kits on the web for home assembled CCDs

This ready built CCD is available.