Measuring CCD Camera Performance
At some point one needs to assess the performance of their CCD camera. Knowing certain information about your camera will allow you to take images that consistently meet the requirements of your image processing software and provide you with the highest possible image quality. Measuring the performance of a camera is not a trivial matter. It requires some understanding of the different camera characteristics and detailed planning for how to collect camera information. I recommend a book and software as aids to understand more about astronomical imaging and also about how to perform measurements and understand the meaning of them. The book is The Handbook of Astronomical Image Processing, by Richard Betty and James Burnell. The software is AIP4WIN. Both can be purchased as a package from WillBell, Inc, from their website: www.willbell.com.
Five characteristics determine the health of a CCD camera:
- Conversion factor or gain
- Readout noise
- CCD linearity
- CCD uniformity
- Dark current
Basic CCD testing covers the first two characteristics; advanced testing covers all five and also the user to see if radio frequency interference and/or charge skimming exists.
The AIP4WIN software includes functions needed to measure CCD camera performance using test images.
Purpose of CCD Camera Testing
A properly operating camera is highly desirable when performing astronomical imaging of any kind. A good time to check the camera performance is when you first start to use the camera. After that, it is a good idea to periodically (every 6 months or so) check it to see if any problems have started to occur as they are likely to affect image quality. Some problems can be corrected by the user during imaging or post-processing, but the important thing is knowing one or more problems exist so steps can be taken to minimize or eliminate their effects.