Altair 290M sensor analysis has dramatically changed

Discussion of features and issues relating to Altair Astro Cameras
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oopfan
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Altair 290M sensor analysis has dramatically changed

Post by oopfan » Wed Apr 03, 2019 4:49 pm

Robin,

When SharpCap 3.1 Beta was released October 2017 I jumped on the bandwagon. I kept up with each minor revision and on January 9, 2018 I ran sensor analysis on my new Altair 290M (see attachment entitled "Altair GP290M Sensor Analysis MONO12 2018-01-09.png".) Afterwards I used The Brain a few times but after joining AAVSO I acquired sufficient confidence to make imaging decisions on my own.

Fast forward to present day. I visited the Altair website and discovered that sensor analysis dramatically changed (see attachment entitled "Altair GP290M Sensor Analysis MONO12 2019-04-03 Altair Website.jpg".)

Honestly this wouldn't have been a big deal if the definition of "Gain 100" and "Gain 200" remained the same but what's happened is that "Gain 100" now describes the characteristics of "Gain 200", and "Gain 200" now describes "Gain 400". The key point I want to make is that I continued to use that original sensor analysis to make decisions regarding gain and full well depth.

I just ran Craig Stark's method for measuring gain by using flats described here:

http://www.stark-labs.com/craig/article ... D_SNR3.pdf

Sure enough what I thought was "Gain 200" is actually "Gain 400". How and when did this happen?

Brian
Attachments
Altair GP290M Sensor Analysis MONO12 2019-04-03 Altair Website.jpg
Altair GP290M Sensor Analysis MONO12 2019-04-03 Altair Website.jpg (122.08 KiB) Viewed 1278 times
Altair GP290M Sensor Analysis MONO12 2018-01-09.png
Altair GP290M Sensor Analysis MONO12 2018-01-09.png (89.14 KiB) Viewed 1278 times

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Re: Altair 290M sensor analysis has dramatically changed

Post by admin » Thu Apr 04, 2019 3:21 pm

Hi,

The 290 series cameras have 2 separate gain modes behind-the-scenes called hCG and LCG. HCG basically has twice the gain of LCG and significantly lower read noise. In either mode you can apply a conventional gain anywhere between the value of 100 and 5000. SharpCap merges the 2 gain controls into a single gain value between 100 and 10,000 – for gains between 100 and 200, LCG mode is used and for gains above 200, HCG mode is used. This automatically provides the best settings for any particular image brightness without the user having to worry about which mode to choose.

While I explained all this? Because your read-out looks like the camera is only operating in HCG mode with a gain limit of about 5000 and as you noted double the expected brightness.

Can you confirm for me what version of SharpCap you are using and whether you using the native SharpCap camera driver for the Altair camera or the Ascom driver?

Cheers, Robin

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