Measurements were performed in 1x1 bin mode. SharpCap was used to capture images, in native 12-bit mode (without 16-bit stretching!). Measurements were done using a central region of images.
A notebook screen covered by several sheets of paper (to reduce light) was used as a constant light source. A room was darkened.
*** UPDATE 2019-11-03 **** Measurements via SharpCap Sensor Analysis tool were made too.
Gain in e-/ADU
The gain was measured through Average ADU vs ADU Variance dependencies. Here is a plot for Gain29:
A slope of the line gives a gain in e-/ADU.
A dependency on the gain in e-/ADU on ZWO gain is shown in the next plot. Note that measured values are in excellent agreement with those reported by the manufacturer (https://astronomy-imaging-camera.com/product/asi120mm-s)
New results obtained via SharpCap Sensor Analysis tool are almost the same.
*** UPDATE 2019-11-03 **** SharpCap Sensor Analysis tool results
Full well
Using measured system gain, it is easy to get the full well:
Full well for ZWO Gain = 0 (3.5 e-/ADU) was measured as 14.3 ke-. ZWO reports 13000 in "Product description" or 14.5 ke- in the corresponding plot. New results obtained via SharpCap Sensor Analysis tool are almost the same.
*** UPDATE 2019-11-03 **** SharpCap Sensor Analysis tool results
Read-out noise (RON)
RON, measured from zero-exposure frames, was found smaller than reported by ZWO and almost equal for different gains: ~2e-. This is strange. See also new results obtained via SharpCap Sensor Analysis tool.*** UPDATE 2019-11-03 **** SharpCap Sensor Analysis tool results
Dark current
The AAVSO DSLR Observing Manual shows troubles while measuring the dark current of DSLR camera sensors. I have to admit that my results for ASI120MM-S are also quite uncertain. I've tried to estimate dark current from values of mean pixel intensity of dark images (1st way) and through standard deviation of mean pixel intensity. The camera has no cooler/temperature regulator which introduces additional uncertainty. The values of the dark current were estimated as ~1 .. 2 e-/s/pixel at room temperature. Additional measurements are needed!Linearity
The sensor was found to be very linear:
Strange behavior at low ADU for another CMOS sensors was mentioned by Mark Blackford for Canon EOS 600D (https://www.aavso.org/comment/47248#comment-47248) and by Christian Buil for cooled ZWO ASI1600MM camera (http://www.astrosurf.com/buil/CMOSvsCCD/index.html). Buil thinks that that behavior is caused by imperfect timing for very short exposures he used. I think it is not an exposure timing problem rather some features of the CMOS sensor itself (autotuning of dark level?). The next two plots were obtained using dimmer light and longer exposures, it is seen than "stranges" arose at the approximately the same ADU level:
*** UPDATE 2019-11-03 **** Table of results obtained via SharpCap Sensor Analysis tool
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