ASI2600MC-P Sensor Analysis - no HG mode?

[Cyendrey]

I just went through the Sensor Analysis of my ASI2600MC-P. It ran without problems, but I do have a question on the results. In the display of gain/ev/Well depth, the well depth steadily increments down.

The problem is, at least according to ZWO ASI documentaiton, is the ASI2600 switched to high gain mode at a gain setting of 100, recovering most but not quite all of the well depth it had a 0 gain. It then begins incrementing down again from that point.

So does Sharpcap just extrapolate the well depth mathmatically without 'knowing' about the HG mode? Or is this a 'real' measurement that is indicating that there is a problem with the Camera, the driver, or with ZWO's statements on HG mode?

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[admin]

Hi,

the full well depth is calculated by multiplying the number of ADU values that the camera has (in this case 65536 - 2 to the power 16) by the e/ADU value for a particular gain. e/ADU values are measured directly for minimum gain and then for other gains they are the e/ADU for the minimum gain divided by the relative brightness of the specified gain.

So, for instance SharpCap has measured that at gain 100, the image is 2.51 times brighter than at gain 0 (the same brightness is achieved with an exposure time that is 2.51 times shorter). That means that the e/ADU for gain 100 must be the e/ADU for gain 0 divided by 2.51 - that gets the 0.31 shown in the table. Then multiply the 0.31 by 65536 to get the ~20600 FWD.

These figures agree to within a reasonable margin of random error with those shown in the graphs on the ZWO website.

What does that mean in relation to HCG mode turning on at gain=100? Well, you certainly do not recover the FWD of minimum gain - that's not going to happen, but you *do* recover most of the dynamic range, since you can see that the read noise also drops by a factor of more than 2 when you switch into HCG mode, which compensates to a large degree for the loss of FWD (as long as you take shorter exposures to avoid excessive saturation).

cheers,

Robin