Brain giving strange results

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cuivenion
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Brain giving strange results

Post by cuivenion » Fri Mar 29, 2019 4:22 pm

Hi, I'm using an ASI224 to image dso's. I've tried using the brain but the result sometimes don't make sense to me.

For example the brain often suggests 18 gain for unity gain and 61 gain for high dynamic range. Surely this should be the other way round.

I've done my best to make sure there are no stars or nebulousity in the roi box.

ippiu
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Re: Brain giving strange results

Post by ippiu » Fri Mar 29, 2019 7:02 pm

I'm interested too...

Asi294: my brain suggests gain 121 and 15 sec....but if you use those settings, almost nothing appears. And even if you do a strong strecthing to the histogram, very few signal comes out.
So i think something in the brain doesn't work properly...
I repeated the sensor analysis twice, also at -15 °C, but nothing in the brain changed...
W.O. RedCat 51 + Asi294 Pro + IOptron Cem25EC + Optolong L-Enhance 2" + Idas D1 2"

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admin
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Re: Brain giving strange results

Post by admin » Fri Mar 29, 2019 8:33 pm

Hi,

It be really helpful if you could post the sky brightness that the brain measures along with this sort of post as with that information there is enough info to work out exactly what is going on.

Cheers, Robin

ippiu
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Re: Brain giving strange results

Post by ippiu » Fri Mar 29, 2019 8:43 pm

In my situation bothr with lps idas filter mounted, and without it, the brain gives more or less the same result.

Sky brigthness measured with idas filter: 2-3
Without filter: 5-6

Brain suggest gain 120 and exposure 15-18 sec, with 10% read noise limit.
W.O. RedCat 51 + Asi294 Pro + IOptron Cem25EC + Optolong L-Enhance 2" + Idas D1 2"

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Re: Brain giving strange results

Post by admin » Fri Mar 29, 2019 8:55 pm

Hi,

The 294 sensor switches between 2 modes called low conversion gain and high conversion gain at a gain of about 120 if I remember correctly. When the gain is above 120, it goes into HCG mode, which has a much lower read noise. By taking advantage of the lower read noise, you can take shorter sub- exposures and more of them and get a higher signal-to-noise ratio in the final stack than by using a slightly lower gain which ends up in LCG mode with a much higher read noise. Have a look at the sensor read noise charts on the ZWO website and you will see what I mean.

A rough rule for what the brain will suggest is 10 times read noise squared divided by the sky brightness figure. This ties in pretty well with the suggestion that you are getting. Remember that the calculation that the brain is doing is not aiming to make any particular target visible in the individual sub- exposures – it's aiming for the minimum noise in the final stacked image over an hour of imaging without extending sub- exposure length for no additional benefit.

Hope this helps, Robin

cuivenion
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Re: Brain giving strange results

Post by cuivenion » Sat Mar 30, 2019 2:32 am

Cheers Robin hopefully I'll be next week when I can test it out.

ippiu
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Re: Brain giving strange results

Post by ippiu » Sun Mar 31, 2019 5:12 pm

Last night brain recommended me these settings...
brain.jpg
brain.jpg (174.06 KiB) Viewed 635 times
But after applied those settings that brain recommended, the image was so dark that live stacking wasn't able to stack each image (it was obvious with these settings)...
live stacking_con impostazioni brain.jpg
live stacking_con impostazioni brain.jpg (181.96 KiB) Viewed 635 times
W.O. RedCat 51 + Asi294 Pro + IOptron Cem25EC + Optolong L-Enhance 2" + Idas D1 2"

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Re: Brain giving strange results

Post by admin » Sun Mar 31, 2019 9:11 pm

Hi,

Okay, I think I see what is happening – although the brain calculation is giving you the correct gain and exposure to ensure that camera read noise will not degrade your final stacked image, there are not enough bright stars visible in the field of view for any stacking to happen at all!

In this case, you would be best using a longer exposure – just long enough to get consistent star detection working. If that pushes the exposure beyond the limits of your mounts tracking, then increase the gain instead. The brain calculations do not take into account this particular aspect of enough stars being visible for stacking to proceed as I have not seen this particular problem before.

If there were enough stars for stacking to proceed then you should find that you would achieve final stacked images of equivalent quality by using the suggestions made by the brain calculations or by using significantly longer sub exposure lengths – even if the target galaxy or nebula was only barely visible in the shorter subs.

Hope that makes sense, Robin

donboy
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Re: Brain giving strange results

Post by donboy » Tue Apr 09, 2019 6:50 pm

If you are using the ASI294 Sensor Library profile in ver 3.2 it is not correct.

You will need to over write it using the one in the Sensor Library from the ver 3.1.

Don

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Re: Brain giving strange results

Post by BlackWikkett » Tue Apr 09, 2019 7:43 pm

Also have a look at your alignment tab in Live Stacking. See how many stars are being detected. If not enough stars try increasing the digital gain. Normally Live Stack only needs 10 stars to align frames for stacking. I'd keep increasing the digital gain until enough stars are detected to align and stack. Alternatively while testing you can always uncheck align frames temporarily and you'll at least get an image to stretch.

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