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Old 27-04-2008, 08:23 AM
Alchemy (Clive)
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Alchemy is offline
Join Date: Jul 2007
Location: Yarra Junction
Posts: 3,044
How do you set the offset for CCD cameras

i have been looking at a new camera purchase QHY8 and am trying to sort out all the "issues" prior to purchase.

My question is this as per thread title , how do you set the offset..... i have done some reading and gathered the following.

Quote from WIN4AIP.

Although it is tempting to expect the signal to noise ratio to be (formula) that simply is not true. the reason is that although you have calculated the mean value of x in ADU (analog to digital ratio- amount of signal which includes noise) you dont actually know whether zero ADU means zero photons . in many types of measurement, and in all CD cameras , the zero point in ADUs is OFFSET from the true signal level. This zero offset is called the signal bias , or just plain bias. In other words when zero photons fall on the detector the camera reports a bias signal usually a small positive value such as 100

So do you simply shoot with the cap on and try different values til you get a clean frame , will it vary with exposure time, is it time dependant, or is this just being too simplistic?

Having only dealt with digital cameras till now its been point and shoot, the technical difficulty has ben ramped up anotch (not ready for the next level mono just yet)

im sure someone with CCD experience can make it simple to understand , and give a practical explanation of how to do it.
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