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Topics - Stonius

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General / Averaging integration doesn't...uh, average
« on: 2018 December 02 02:27:55 »
Take 4 dark frames.

12 bit mean values as follows;

51.47
51.47
51.47
51.46

Average them and you get 51.4675, right?

But, if you take those frames and integrate them using averaging, no noise evaluation, no weighting and no pixel rejection, you get;

Average 51.4682 (and Median gives you 51.4353).

Which is 0.007 higher than a straight up mathematical averaging.

I wonder what's going on?

Is the 'statistics' proccess limited in it's reporting, or is something funky happening during integration?

Anyone know?

Cheers

Markus

2
General / Non-linear Dark current
« on: 2018 November 26 18:41:43 »
Hey all, I've been following Craig Stark's tutorial on defining your camera's noise characteristics.

According to him, Dark Current should show a linear regression.

I notice my dark current over time increases in a non-linear fashion, more inline with a power series (y=ax^b rather than y=ab^x).

I'm assuming that the dark current scaling algorithm in Pixinsight expects a linear regression (twice as much time = twice as much dark current), so for me the scaling won't work.

I guess I could just take dark flats, but I'd ultimately like to figure out why this is so.

Someone suggested amp-glow may account for this non-linearity.

It could also be an issue with my bias frames which are required for this calculation, but I can't think what. As far as I can tell, the bias and resultant integrated master are fine. Just to be sure, I took the bias series at the same settings as the darks (except for exposure length, of course!)

ASI1600MM Pro, Filterwheel plugged through cameras onboard hub.
Slowest download speed (40). Cable from 1600 going direct to computer
Set point -15 C
It seems a consistent curve shape at exposures ranging from 30 to 600 secs at all gain levels.

Many thanks for any help.

Markus

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