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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.



#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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