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Are there any guide lines for how much gain to use?

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#1 BobW55

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Posted 13 August 2019 - 09:14 PM

I am using a ASI294MC Pro into a ES ED102 FDC100.

I am also using Asiair.

 

So far I have been just trying to find the best preview image balancing gain with exposure time.

Is there a chart or other set guide lines what how much of each to use based on target?

I am already seeing that a nebula needs way different from a Galaxy.

Or do I just need to start taking notes and play around till I see what works.



#2 bobzeq25

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Posted 13 August 2019 - 09:27 PM

It's tradeoffs.  The more gain you use the shorter your subexposure time, which helps if your mount isn't great.  What you lose is dynamic range and some star color.

 

"Unity" gain, where 1 adu is 1 electron is a reasonable place, as a general rule.


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#3 RazvanUnderStars

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Posted 13 August 2019 - 09:56 PM

Further to Bob's message, you have a chart with dynamic range vs gain in the camera's manual (see pg 8).


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#4 BobW55

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Posted 13 August 2019 - 10:07 PM

Yes I have seen that, but ASIAIR does not give such settings.  I can adjust gain, temp, and exposure time.



#5 Pauls72

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Posted 13 August 2019 - 10:20 PM

As bonzeq25 said, Unity Gain. Which for your ASI294MC-Pro is 117.

Your images may show very little data. But after you stack them, give them a stretch and apply some curves they will pop.

 

This was taken with an ASI294MC-Pro at Gain=117, Offset=20, Temp=-10C, 13 x 300 seconds, plus calibration frames.

So here is what 1 RAW sub looks like and what the processed image looks like.

 

M51-RAWs.jpg

M51-ST-processed-S.jpg

 

 


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#6 RazvanUnderStars

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Posted 13 August 2019 - 10:41 PM

Also, if you can temporarily connect it to a computer with SharpCap, you can run the analysis described at https://www.sharpcap...smart-histogram, which also takes into account the sky brightness level. Even if you don't use, I think the page will be useful as it talks exactly about what you asked.


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#7 Midnight Dan

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Posted 14 August 2019 - 08:42 AM

DO NOT use unity gain on the 294 camera!  Go the the ZWO web page for the camera and scroll down to look at the graphs.  You'll see there is a step function in read noise and dynamic range.  Unity gain is on the wrong side of that step!

 

In one of the graphs, they have labelled a gain of 120 (slightly above Unity), as the point where you get a big drop in read noise, and you get maximum dynamic range.  For this camera, I can see no reason to ever shoot at any other gain for normal imaging.

 

In your note, you mention "preview" images.  If you're just trying to get a quick view of the target for framing, that's a different story.  Crank the gain up to whatever you want - doesn't matter much.  

 

-Dan


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#8 davidparks

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Posted 15 August 2019 - 09:13 AM

As Dan states, ZWO's 294 has a High Conversion Gain mode (HCG) which executes at 120 gain.  This significantly reduces noise without losing any dynamic range.  There is no reason to ever use less than 120 gain with the 294. 

 

The 294 is a wonderfully sensitive instrument, and with the HCG mode keeping the noise normally associated with higher gains extremely low, this camera is great for high gain, short exposure work ideal for EAA (losing a bit of dynamic range isn't too bad for observational stacking).  Keeping the gain @ 120 preserves the 13 full stops of dynamic range, and makes for great traditional long integration astrophoto work.


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#9 the Elf

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Posted 15 August 2019 - 12:32 PM

Here is Robin Glover's oppinion (the autor of sharpcap):

https://www.youtube....h?v=ub1HjvlCJ5Y

 

BTW: this is the talk he referes to, where he ran out of time:

https://www.youtube....h?v=3RH93UvP358

(I love the into, read this in one second: "howsitgoinev'ryb'dyRuzeenhereforastrofarsography". Challanging for non native speaker to say the least.)


Edited by the Elf, 15 August 2019 - 12:37 PM.

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#10 tsk1979

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Posted 17 August 2019 - 03:32 AM

Great info in the videos

Could find read noise on the forum itself.

Looks like 20s exposures in Dark skies is great on my F4 lens, for A7S I should use ISO 2000 instead of 4000 and for my A7 I should use ISO 1000



#11 bobzeq25

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Posted 17 August 2019 - 10:48 AM

For Canons/Nikons, it's recommended to use only the standard ISOs, 200/400/800/1600/3200...  The intermediate ones use a method which is not helpful.  Not sure if that applies to Sonys.


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#12 ericthemantis

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Posted 17 August 2019 - 11:29 AM

Yeah, "in-between" ISO values usually are applied with digital processing (ie the same thing as stretching post), so no benefit, only potential for more quantization/truncation error before writing to file. But I think I saw some cameras that actually apply these in between ISO steps in analog. You can check by seeing if the noise in your bias frames changes. If it changes, analog step. If it stays about the same, most likely digital step.
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#13 p3aul

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Posted 22 August 2019 - 09:54 PM

Wow! and that was just one image after processing? No stacking?

Paul



#14 Pauls72

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Posted 23 August 2019 - 12:42 PM

Wow! and that was just one image after processing? No stacking?

Paul

It was 13 light subs and 10 dark subs stacked and then processed.

 

This is a single stub with no calibration frames with some quick processing done.

 

Single-Sub-Processed.jpg


Edited by Pauls72, 23 August 2019 - 12:55 PM.


#15 BobW55

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Posted 23 August 2019 - 09:12 PM

Since they have updated the firmware on the ASIAIR,  I have found a gain of 120 to be just fine.  

It is the histogram you have to adjust around a bit, the Auto function of it does not always produce the best images.

I am slowly getting things dialed in.  

 

10 @ 60 second exposures.  Done in Nebulosity and very little post processing.

 

ProcM57.jpg

 



#16 p3aul

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Posted 26 August 2019 - 10:33 PM

It was 13 light subs and 10 dark subs stacked and then processed.

 

This is a single stub with no calibration frames with some quick processing done.

 

attachicon.gif Single-Sub-Processed.jpg

Still Wow! I just bought a used LX200 8" GPS like new. Cloudy and rainy here with no chance to look. I was thinking about getting that Celestron 5MP camera and see what it would do with a DSO. If I could get an image like that second one I would be satisfied! I have Adobe Creative Suite subscription and could process it in Photoshop.I believe I could do that.



#17 bobzeq25

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Posted 27 August 2019 - 12:41 AM

Still Wow! I just bought a used LX200 8" GPS like new. Cloudy and rainy here with no chance to look. I was thinking about getting that Celestron 5MP camera and see what it would do with a DSO. If I could get an image like that second one I would be satisfied! I have Adobe Creative Suite subscription and could process it in Photoshop.I believe I could do that.

You're headed for a difficult road.  The two chief beginner mistakes are an inadequate mount, and too big a scope.  The LX200 8 inch, unfortunately, qualifies on both points.

 

Look at Pauls72 icon image.  That's the "hot setup" a good equatorial mount and a small refractor.  If your goal is to take images like his, that's the path to go down.

 

A good solution is to forget the big scope, and start out with a camera and a lens.  This excellent book will guide you through the process.  It starts out with a camera and a lens on a tripod, then on a camera tracker (which can be DIY or store bought), and then to a small scope on a good mount.  Scroll down the webpage to the picture of the author.  That's a 70mm refractor (about $500) on a Sirius mount ($1200).  You spend more on the mount than the scope, it's more important.

 

http://www.astropix....bgda/index.html

 

That's a lot of money, so the camera/lens approach is my recommendation.  It will both be excellent learning, and a way to figure out just how far you want to go with this.

 

The mount is the key.  A bigger scope is not better for getting into this, it's (far) worse.  Long exposure imaging of DSOs is nothing at all like visual astronomy.


Edited by bobzeq25, 27 August 2019 - 12:46 AM.

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#18 BobW55

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Posted 27 August 2019 - 10:55 AM

After more reading and more playing around, I have found that a gain setting of 150 works best. (given my total imaging system set up)

I imaged M51  180 seconds 10 subs at a gain setting of 120, 130, 140, up to 200.  I could see a real difference at 150 vs 120  past 170 things did not look so great.

If I am reading the Sharpcap camera analyzer correctly (still not 100% clear on it more play time is needed) this also bears out.

 

M51Crop

 



#19 the Elf

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Posted 27 August 2019 - 11:13 AM

As always (almost always) I agree to Bob (bobzeq25) that the proverbial small refractor on a as-good-as-you-can-afford mount makes things easier, but I keep on telling people that a longer focal lenght is not neccessarily the end of your imaging career. Frustration comes when expectations are higher than the possible result. We do not know what the OP expects so there is no need to dicourage him.

 

Here is my favorite anti example of a far too long focal length on a poor mount:

http://www.elf-of-lo...rlpool2018.html

That's the bad, bad RC6 on the bad, bad AVX with an uncoold camera. The point is: it is much easier with better equippment. For now pick bright and large objects and learn processing and you'll have some decent images. As soon as the objects get smaller and dimmer you will find the setup's limits. It is common practice to upload the unprocessed stack and ask other to work on it to get an idea what is in the data. When beginning it is always difficult to know if the result is limited by the data itself or be one's own processing skills. I'd be pleased to do a quick processing of your M51.


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#20 bobzeq25

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Posted 27 August 2019 - 03:31 PM

I keep on telling people that a longer focal length is not necessarily the end of your imaging career.

And I never said it was.

 

Starting shorter is more fun.

 

It speeds up progress, people often are displeased by the time taken up in learning imaging.

 

People will be emailing images to their friends sooner.

 

I'm always going to recommend the best way to those goals.  One of my favorite quotes, from a talented beginner.  I agree with it, including the "possibly".

 

"Sure you can possibly <learn to> image as a beginner with something that is larger or that you may have but holy cow its hard enough with something small."

 

Holy cow, it is.  <smile>

 

By all means express an opposing opinion.  Just don't misrepresent mine, replacing the straightforward "going down a difficult road" with emotionally loaded statements like "end of your imaging career".


Edited by bobzeq25, 27 August 2019 - 03:39 PM.


#21 p3aul

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Posted 27 August 2019 - 05:43 PM

Yes excellent astrophotography takes expensive mounts and telescopes. My interest doesn't lie along that line. If that's your hobby and you can afford it fine. I was only interested in getting an image I could share on FB, not museum quality. I do the same with my microscope. 

 

Paul 


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