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Measuring the QSI 660

20/8/2014

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Receipt of a new CCD camera for me is accompanied by capturing bias, darks and flats for measuring the CCD camera's parameters such as Gain, Readout Noise, Dark Current Noise and Full Well Capacity. These are fairly critical things to know about your CCD camera if you wish to understand how to maximise its performance via such things as using the Optimum Exposures Calculator. QSI cameras are built to allow the user to set the Gain to either High or Low. The High setting is recommended for when imaging unbinned at 1x1 (e.g. for Luminance) as this maximises the ADU (image brightness) produced for a certain number of electrons. The Low setting is recommended for when imaging binned at 2x2 or more (e.g. for Red, Green and Blue). This setting assumes that because of binning, there will be a lot of electrons acquired at pixels to produce signal and so it increases the number of electrons needed to reach a certain ADU (image brightness). Customising these Gain settings when imaging guarantees you maximise your CCD camera's dynamic range. 
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QSI quote their 660 model camera as having a High Gain of 0.2 e/ADU and a Low Gain of 0.5 e/ADU. These values seemed very rounded to me so I thought it best to measure it myself, and for my particular camera. Following Craig Stark's method, I captured a series of flats with the High Gain and Low Gain settings. These were my final graphs:
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The gradients of the lines of best fit being the measured Gain, I found the High Gain setting to produce a Gain of 0.1818 e/ADU and the Low Gain setting to produce a Gain of 0.4255 e/ADU. These values are sensible according to QSI's specifications and are much more accurate. 

To make a long story short, these were my measured parameters overall for each Gain setting at -10°C:

High Gain Setting (for 1x1)
Gain: 0.1818 e/ADU
Readout Noise: 4.0 e
Dark Current: 0.1891 e/minute
Full Well Capacity: 11,635 e

Low Gain Setting (for 2x2)
Gain: 0.4255 e/ADU
Readout Noise: 5.1 e
Dark Current: 0.8510 e/minute
Full Well Capacity: 27,232 e

All perfectly viable values and with extremely low Readout Noise, as is expected for a Sony ICX694 CCD sensor. Dark Current is also extremely low at -10°C, which carves the idea that darks are not really a necessity when working with this CCD sensor. In fact, an insufficient number of darks used in calibration for a master dark would probably introduce more noise than it would remove and I am personally not keen on capturing, say, 50 darks for a good master dark. I assume therefore that bias and flats will be all I will bother with when using this CCD camera. 
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