Sensor Analysis Result vs PixInsight's Basic CCD Parameter Script

[dchavezjr]

Hello,

I just recently did a sensor analysis on my 26M and also did the Basic CCD Parameters Script in PI. Is there a particular reason why the results differ?

In SharpCap's Sensor Analysis I got these values:
Gain value 100
Read noise = 3.6 e-
e-/ADU = 0.74

while in PixInsight I got these:
Gain value 100
Read noise = 1.353 e-
e-/ADU = 0.257

Thanks and clear skies to all!

[admin]

Hi,

How did you get the image data that you fed into Pixinsight? The figures that you got in PI look roughly right for the sensor running in HCG (High Conversion Gain) mode, whereas the SharpCap figures for gain 100 are about right for LCG mode.

SharpCap implements an auto-switchover between LCG and HCG for Altair cameras. This seamlessly merges the gain and the LCG/HCG switch together to ensure that the camera is always running in the best mode depending on the total amount of gain requested. This is possible because the switch from LCG to HCG adds an extra amount of gain (3.0x brighter in the case of the sensor in the 26C/M).

So...

SharpCap Other Software Brightness increase over gain 100

Gain 100 Gain 100, LCG 1.0x
Gain 200 Gain 200, LCG 2.0x
Gain 299 Gain 299, LCG 2.99x
Gain 300 Gain 100, HCG 3.0x
Gain 600 Gain 200, HCG 6.0x

This is why you see a big drop in the read noise graph at gain=300 if you look at the sensor data produced by SharpCap - that's where the LCG/HCG changeover happens.

cheers,

Robin

[dchavezjr]

Hi Robin,

Thanks for the reply.

I followed the procedure in PI to obtain the images I fed to PI. That is, 2 Bias frames, 2 Flat frames and 2 Dark frames (5 sec and 50 sec). In NINA I used a Gain value of 100, an Offset of 50 and HCG is set to On. Ultra was also chosen.

I am thinking on what Read noise to use in calculating the correct subexposure length using the formula in Linda's Astronomy Adventure (YouTube).

Regards and clear skies!

[admin]

Hi,

OK, so that all makes sense with PixInsight analyzing HCG images created in NINA and therefore getting results typical of HCG mode. As noted, if you want HCG mode in SharpCap, set gain to 300 or above (correct for 26M/C cameras - the exact value where HCG kicks in depend on the sensor model in use).

The read noise will depend on which gain you pick and whether you go HCG or LCG. You could consider using SharpCap's 'Smart Histogram Brain' function which will do all the sub-exposure length calculation for you (including considering the effects of using different gains and working out which is best). See https://docs.sharpcap.co.uk/4.1/#The%20 ... n%20Window

cheers,

Robin