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Gain x Offset for EAA?

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#1 GazingOli

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Posted 20 September 2020 - 05:00 AM

I am still trying to figure out how go get best results for my equipment... in the beginning I tried to keep gain low but learnt that high gain is good and with propper darks no problem. Just forgot to adpt the offset. Now the question is which offset matches which gain?

 

DarkTable.jpg

 

That is what I thought might be a good setting. Top row is exposure time in sec, left column ist gain / offset. Camera ASI224. I tested gain 500 with offset 190 and it seemed to be good. From that on I estimated the lower settings. I prepared all the darks this morning and will test asap.

 

Any comments?

 

CS.Oli


Edited by GazingOli, 20 September 2020 - 05:08 AM.


#2 Noah4x4

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Posted 20 September 2020 - 09:06 AM

I use Sharpcap and its awesome Sensor Analysis/Smart Histogram Tool. Set the Gain to a point where the two Smart Histogram green bars are the same length ( in logarithmic mode). Set exposures to a point where the steep curve is just to the right of the left had end of the green bars. Easy. 



#3 Todd1561

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Posted 20 September 2020 - 09:11 AM

I’d be interested in hearing what the experts have to say on this. Correct me if I’m wrong but ‘offset’ is the equivalent of the ‘brightness’ control in SharpCap (at least with ZWO cameras) correct? I’ve always been confused on how to use this control. I’ve found that placing it too high wreaks havoc with flat frames.

I’m certainly not trying to hijack this thread, so if this isn’t inline with what Oli is asking just let me know and I can make another thread.
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#4 GazingOli

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Posted 20 September 2020 - 09:54 AM

Thanks Noah for the tip where to dig on - just do not understand anything at the moment an on spontaneous trial ther was only one green bar moving at all. I will go through the manual and maybe I find some kind of video howto, where I can see how things should happen. Sure something that help me on!

 

As far as I read I will have to do a sensor analysis first - correct?

 

Todd: as far as I know brightness and offset are the same

 

CS.Oli



#5 GazingOli

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Posted 20 September 2020 - 10:58 AM

so... I tried sensor analysis. Sent an even grey image to my smartphone and put the camera on it... first image too bright. Ok. Made it darker. Now it is too dark, SharpCap recommends to consider a brighter. Ok... again. Now it seems to work but then at the end another error message: could not determine exposure time. Use a brighter surface.

 

So what can I do? Either I am too bright or too dark.

 

CS.Oli



#6 GazingOli

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Posted 20 September 2020 - 11:33 AM

ok ... it worked. Maybe I missed part where I had to cover the nosepiece of the camera.

 

Next step is using the smart histogramm which I need to have the scope and filter on, as far as I understood. Does Sharpcap know where to find the analysis data?

 

I guess I have to capture a darkframe when everything is set before I can start capturing images.

 

CS.Oli



#7 garyhawkins

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Posted 20 September 2020 - 11:46 AM

I need to do a sensor analysis - so far I've just been winging it!  Another great feature in SharpCap.

 

Thanks Noah for the tip where to dig on - just do not understand anything at the moment an on spontaneous trial ther was only one green bar moving at all. I will go through the manual and maybe I find some kind of video howto, where I can see how things should happen. Sure something that help me on!

 

As far as I read I will have to do a sensor analysis first - correct?

 

Todd: as far as I know brightness and offset are the same

 

CS.Oli



#8 donstim

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Posted 20 September 2020 - 03:11 PM

I am still trying to figure out how go get best results for my equipment... in the beginning I tried to keep gain low but learnt that high gain is good and with propper darks no problem. Just forgot to adpt the offset. Now the question is which offset matches which gain?

 

attachicon.gifDarkTable.jpg

 

That is what I thought might be a good setting. Top row is exposure time in sec, left column ist gain / offset. Camera ASI224. I tested gain 500 with offset 190 and it seemed to be good. From that on I estimated the lower settings. I prepared all the darks this morning and will test asap.

 

Any comments?

 

CS.Oli

To match the gain and offset, I use this method suggested by Robin Glover, the creator of Sharpcap:  https://forums.sharp...&start=50#p6863

Others recommend a gain a bit higher to make sure the bottom end isn't clipped, but his method should do that plus allow maximum headroom for the high end dynamic range. Use the same offset (or brightness if you want to call it that) for your darks, flats, and light frames.

 

Then use either the Smart Histogram as Noah suggested, SharpCap's Brain tool, or your own experience/needs to choose a gain and exposure setting.

 

I need to do a sensor analysis - so far I've just been winging it!  Another great feature in SharpCap.

Shouldn't need to do that Sharpcap already has a sensor analysis for your cameras built into it. You can see the cameras for which sensor analyses are included in the SensorLibrary folder oh whatever directory you installed Sharpcap in (e.g, mine is C:\Program Files\Sharpcap 3.2 (64bit)).


Edited by donstim, 20 September 2020 - 03:16 PM.

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#9 GazingOli

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Posted 20 September 2020 - 03:45 PM

at the moment nothing works anymore as it should be! I really regret to have started all this. so be careful everybody! it is not that easy!!!

 

As soon as I try to use darks it does not work anymore. does anybody know how to reset sharpcap?

 

 

CS.Oli


Edited by GazingOli, 20 September 2020 - 03:48 PM.


#10 GazingOli

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Posted 20 September 2020 - 04:22 PM

main problem is obviously the darks... then all the other settings are mixed up... at least I can work again...

 

desperately Oli



#11 selfo

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Posted 21 September 2020 - 09:46 AM

I’d be interested in hearing what the experts have to say on this. Correct me if I’m wrong but ‘offset’ is the equivalent of the ‘brightness’ control in SharpCap (at least with ZWO cameras) correct? I’ve always been confused on how to use this control. I’ve found that placing it too high wreaks havoc with flat frames.

I’m certainly not trying to hijack this thread, so if this isn’t inline with what Oli is asking just let me know and I can make another thread.

 

See if this helps..

 

https://forums.sharp...opic.php?t=1925


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#12 Todd1561

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Posted 21 September 2020 - 09:46 AM

at the moment nothing works anymore as it should be! I really regret to have started all this. so be careful everybody! it is not that easy!!!
 
As soon as I try to use darks it does not work anymore. does anybody know how to reset sharpcap?


It sounds like you got it mostly sorted but for future reference you can reset your camera settings to default in SharpCap by holding the Ctrl key when connecting to the camera.
 
Link to docs it's under the 'Automatically restore camera settings' heading.

Edited by Todd1561, 21 September 2020 - 09:54 AM.

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#13 GazingOli

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Posted 27 September 2020 - 03:08 PM

so I finally reset everything... (thanks Todd!)

 

Anybody who wants to try sensor analysis, make shure that you

- note or screenshot all your settings

- save your darks in a separate folder

- be aware that this is not a simple business and will take some time

 

CS.Oli


Edited by GazingOli, 27 September 2020 - 04:15 PM.


#14 Noah4x4

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Posted 27 September 2020 - 06:20 PM

so I finally reset everything... (thanks Todd!)

 

Anybody who wants to try sensor analysis, make shure that you

- note or screenshot all your settings

- save your darks in a separate folder

- be aware that this is not a simple business and will take some time

 

CS.Oli

You need to get the light balance perfect. Not easy. Took me ages with my Atik Horizon camera.

 

However (and I might be wrong) I thought Robin Glover had already completed Sensor Analysis for most ZWO cameras and such data is inherent in Sharpcap,  so all you then need to is select camera, open the Smart Histogram, select logarithmic mode, line up the two green bars using Gain, put the Steep part of the curve to the right of their left edge to fund exposure. I also created and saved series of named Capture profiles so I can be close to where I need to be in one push of a button. 


Edited by Noah4x4, 27 September 2020 - 06:20 PM.

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