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INDI Library v1.9.5 Released (08 Mar 2022)

Bi-monthly INDI Library released with new drivers and bug fixes.

ASI Camera - Gain/Offset/x-Bit

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Thanks a lot for sharing! Maybe the observation spot I am using for testing is too light-polluted?

When you say, fitsviewer auto‘s everything, do you mean the autostretch function is enabled? In my case it is disabled.

Could you kindly share also a screenshot with the „control“ settings of the asi drivers? Just that I can cross-check if I messed up accidentally any other parameter.
4 years 1 week ago #25911

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It could be very useful to have a comprehensive ASI camera guide as Jasem suggested. Think I'm not good enough to write it but I can contribute with my personal experience on a specific camera (ASI071 pro).
- My setup is a 115/800 f/a 6.95 apo refractor on a HEQ5 mount.
- Added a field flattener and LP filter. No focal reducer.
- Cooling always at -10. It's a low noise camera, there's no real gain to cool it further (as to specs on ASI website, astronomy-imaging-camera.com/products/as...ameras/asi071mc-pro/).
- Tried unity gain at first, then settled on 240 gain with 300s exposures . It doesn't seem to saturate too much (see attachments for M101, M81. deepsky objects that you can easily compare with yours). Probably would change for M31 or M42.
- Ignored offset as another owner on Cloudynights says it's now fixed at 50. Not really sure about that.
- Beside gain I left all other controls to their default values.

Overall I'm satisfied with these settings but please give me your opinion, there's always a benefit in trying different approaches.
Ferrante

attachments:
- ASI071 'Control' tab from Ekos/INDI
- M81 single raw 300s exp @gain 240 + histogram
- M101 single raw 300s exp @gain 240 + histogram
- M101 single debayered 300s exp @gain 240
4 years 1 week ago #25915
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Replied by Greg on topic ASI Camera - Gain/Offset/x-Bit

I’m writing a guide on exposure and there are a couple of goals you can strive for in your settings. I won’t explain why for now as it will be in the guide.

One is to place the sky background peak at 2.2% of the full scale on a linear histogram like in fits viewer.

The second is to set your camera ISO/gain such that you have 11 stops/64 dB of SNR.

With regards to offset, I don’t see this as an important factor as any image will only have usable content above the background level, which is to be set at 2.2% as mentioned. So 0 offset is probably fine.
4 years 1 week ago #25921

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Are the sensors really that uniform, one could take the values from others? I took biases with the qhy168 I got from a mate for gain 0, 5, 9, 11, 12, 13 ,14. For each gain set, I watched the histogram of the bias and adjusted the offset value, so that nothing of the left "foot" of the histogram was clipped to black.
The higher gain came, the higher the offset was to be set not to clip anything on the left side. The resulting offset/gain table was not linear in this case. I think in principal this should work the same way with any cmos cam.
These offset values then should be applied to all light and calibration frames of course.
What I don't understand is: why do manufacturers not normalize their setting to 0-100%, so every cam has different max gain settings now?

Andreas
4 years 1 week ago #25922

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@ gbeaton:
I think this is a misconception. Calibration frames like bias or darks might be clipped on the left side of the histogram with offset 0. This could introduce artifacts during calibration.
jonrista.com/the-astrophotographers-guid...oise-and-histograms/
scroll down to "Anatomy of Signals in Histograms". The offset value prevents the "separation" of beeing negative.
Andreas
Last edit: 4 years 1 week ago by Andreas.
4 years 1 week ago #25924

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Replied by Greg on topic ASI Camera - Gain/Offset/x-Bit


Yes, you could be right. I forgot to mentioned that as far as offset goes, I haven't studied it.
4 years 1 week ago #25930

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Helge,

Yes, I set kstars fitsviewer settings to include autostretch and occasionally debayer as was in that image. I included my settings page for both cameras. I hope you have better luck with the camera.

WHERE is everyone getting this gain of 50 for HDR on the asi cooled cmos cameras? I keep seeing post with that value included but it's not what Sam at ZWO states as Highest Dynamic Range (widest range of signal that the sensor can record) Cooled ASI Camera Settings
The following user(s) said Thank You: Helge
4 years 5 days ago #25957
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Replied by Greg on topic ASI Camera - Gain/Offset/x-Bit


It’s not camera dynamic range you are trying to achieve. It’s star SNR. If you have high gain the bright stars with high SNR will be saturated. These are all trade offs of course so it’s also related to exposure time. Because you probably have to have longer exposures for guiding to smooth things out. You’ll have to turn down the gain. You can corroborate what I’m saying with PHD2 “best practices”
4 years 5 days ago #25958

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Gain does not make your camera more sensitive. It boosts the noise as well as the signal and does not help the signal to noise ratio (SNR) in and of itself. Gain trades off dynamic range and quantization error.

It is camera dynamic range I am trying to achieve when I want the faintest signal and also stars with strong signal to be recorded. I am referring to taking images of DSO's with my cooled ASI071mc-pro.

With your comments above, it looks like you are referring to guiding that has exposures less than 5s where noise is not as important to manage as it is in a main imaging camera. I want the sensor well on my main camera to fill up slowly with the stronger signals to give the fainter signals time to register on the histogram without oversampling. GAIN AND OFFSET EXPLAINED ....the statement about gain above is in bold on this article.
4 years 5 days ago #25960

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Replied by Greg on topic ASI Camera - Gain/Offset/x-Bit

Maybe I lost track of the thread but the 50% was a reference to a question Helge had about an ASI guide cam setting.
4 years 5 days ago #25962

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Replied by Matt on topic ASI Camera - Gain/Offset/x-Bit

Just curious if there ever was a guide created, as Jasem had proposed, for folks who have ASI cameras? To date I have always used my ASI071MC through USB3 direct to a USB3 enabled laptop. Now that I have a stellarmate any options that might help mitigate amp glo through USB2 using this camera would be good to know. To bad ZWO don't offer a trade in for the MC -> Pro version :)
3 years 3 weeks ago #38260

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Hi Kes74,

To my knowledge, there is no guide - but in case it is useful, this is, what I have been putting down some time ago. I could not find the electronic version, just a sheet of paper...sorry, it does not look very nice.

Best, Helge
3 years 3 weeks ago #38273
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