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INDI Library v2.0.6 is Released (02 Feb 2024)

Bi-monthly release with minor bug fixes and improvements

ASI Camera - Gain/Offset/x-Bit

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I would suggest that anything you see below 30 seconds of exposure is not really representative of the sensor for long exposure. Spend an evening testing your rig on a variety of objects with Unity exposures up to 120-240sec. A dozen of each to give you some SNR to play with. Diligently acquire bias, flats and darks (even if you dont advocate using all types of calibration frames, it will expose a better understanding of how the camera works).

Then process your images like you mean it.
Skywatcher 190MN - EQ6 Pro (with Belt Mod) - ASI1600MM-Cooled - ASI EFW7 - ASI120MM - WO f4 Guide Scope - Rigel nStep - KStars/Ekos - KDE - PixInsight
6 years 7 months ago #18823

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Quick question on the scale applied by the ASI ZWO indi driver for the gain and offset. In EKOS ASI071 Control settings I can shift the slider for the gain between 0 and 600. If I wanted to set the gain to 90, as suggested for the unity gain, is this 1:1 the same parameter value on EKOS?
6 years 3 weeks ago #23918

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If I may come back to this one, last night I got completely stuck. I am using an Apo with 500mm focal length (f/6.25), the ASI071MC as primary cam and attached the ASI120 to the OAG prism.

For the ASI071 let‘s assume I am using the unity gain setting, with gain = 90 and offset = 20. When running the solver and the focuser, what could be the ideal gain setting versus exposure (how about 1 sec)? I assume I would not change the offset.

For the ASI120, based on advise in another thread, I will set gain to 50% and set the offset to zero. For guiding (internal guider and phd2) based on these gain/offset settings, which exposure time (seconds?) is generally recommended - am I right that settings will somehow be different when using an OAG compared to a guide scope (e.g. higher gain)?

I am fully aware that „it all depends“ on specific situation, but I could just do with a good „starting point“...

Thanks a lot!!!
5 years 10 months ago #25879

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For guiding I think the camera settings all come down to matching a gain with the guide image interval. 1 sec is probably a good choice. I use the ASI 120 for guiding on a little 50mm f4 guide scope and keep it at its Unity setting. If you're struggling then maybe Bin the capture image and or create a master dark for subtraction.
For focusing with the ASI 071, as Jasem mentioned earlier in the thread, avoid saturating/saturated stars. At F6.25 you shouldn't have too many focus problems. The odd super bright one won't be selected for focusing so pay attention to the median brightest stars as focus candidates. The auto process works very nicely. You can always check with a Bahtinov mask as a confidence booster.
Skywatcher 190MN - EQ6 Pro (with Belt Mod) - ASI1600MM-Cooled - ASI EFW7 - ASI120MM - WO f4 Guide Scope - Rigel nStep - KStars/Ekos - KDE - PixInsight
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5 years 10 months ago #25889

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I wonder if the community can come up with a short guide for ASI users on INDI? It seems there is lots of information out there scattered all over the place which can be confusing and frustrating for new users. A short concise guide with the settings..etc would be really great! What do you guys think?
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5 years 10 months ago #25899

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on another forum I asked about suggested ASI071 Pro gain/offset settings. Reply was:
"The offset for the Pro is now fixed in firmware and cannot be changed. I have heard that it has been fixed at 50.
When I first started using my original ASI071MC I used the unity gain, but I had to use very long exposures to get histograms like I was accustomed to seeing with my DSLR using an ISO of 800-1600. After researching the gain setting on the 071 I settled on gains of 200-300 as being roughly equivalent to ISO 800 on my DSLR. I eventually adopted a gain of 200 as being standard. "
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5 years 10 months ago #25906

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This is very helpful. Tonight I applied unit gain with 2 and 3 minute exposure but images turned out very dark. Also running the focuser with 4x4 binning and for instance 10 sec exposure were not satisfying. For the solver, 2x2 binning and 10 sec exposure worked ok with unity gain setting. Will use try next time higher gain values as suggested.

As regards the ASI120 cam, used as guide cam, the 50% gain and zero offset settings worked pretty well. In Internal Guider, 1.5 sec exposure seem to score good results.
Last edit: 5 years 10 months ago by Helge.
5 years 10 months ago #25908

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I ran unity gain@-10C on my newly acquired asi071 pro two nights ago on the leo triplet. 180s exposures worked out okay. I want to try the HDR setting (0 gain) next session. Helge, I was able to autofocus using a 3.0s exposure binned 2x2 and produced almost a dozen candidate stars to select upon. I used the same settings for solving at unity. I attached a screenshot....ekos gave my images a whacky iso value that I never asked to to assign to the filename. Im using a CLS filter and fitsviewer auto'd everything

On the asi120, mine gave me so many problems with dropped frames that it was almost torture to try to get 25 frames of Leo. I am a fan of the new SEP guiding mode. It seems to measure HFR of the fov to get a better guide star. I'm eyeing the asi290mini as a viable replacement to a camera that i've flashed and fought for a while.
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5 years 10 months ago #25910
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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.
5 years 10 months 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
5 years 10 months 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.
5 years 10 months 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
5 years 10 months ago #25922

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