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ZWO294 MC Pro Regarding gain, do camera's have a "sweet spot?"

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#1 psy1280

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Posted 30 June 2020 - 02:08 PM

I'm new to EAA and recently purchased a ZWO294 MC Pro. Can anyone tell me the best gain setting for this camera using a LP filter with a Celestron 8" SCT alt/az mount.. I only image EAA and was told that every camera has a sort of "sweet spot" regarding gain. Not sure if this is true or whether it depends on exposure, etc., etc. 

 

Thank you,

Joe



#2 BobE102330

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Posted 30 June 2020 - 02:30 PM

I’m a newb, but my take on camera sweet spot is balancing read noise and full well depth to your target and focal ratio.  At low gain you have more full well depth but read noise is higher. So called unity gain is often considered an optimum, but I feel it varies by target.  Brighter targets will give you more signal so it’s easier to swamp the read noise and you’ll want all the dynamic range that you can get. That goes toward minimum gain. Dim targets, on the other hand are signal to noise challenges so go higher gain and give up some dynamic range to get a better image.  It seems like most  people on YouTube settle on unity gain for almost everything and adjust sub duration to get proper exposures. That works, but I suspect at the extreme bright and dim ends adjusting gain per target makes for more optimum exposures. If only I got enough opportunities to test various settings. 



#3 cmooney91

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Posted 30 June 2020 - 03:33 PM

Anything above the High conversion gain crossover point should be good. 

 

If you look at the charts on the ASI294 page you'll see a big step-wise change in read noise and dynamic range after 120 gain. (this is above unity gain 117)

 

The read noise (RN) plummets, and the dynamic range(DR) rebounds back up to its full value. 

 

From there, as you increase the gain, the RN slowly decreases with diminishing returns and the DR range drops linearly.

 

A lower RN is helpful for live stacking since we want short exposures(resulting in less signal).

 

so it's a trade off between RN and DR.  I usually shoot for something between 1/2 and 3/4 max. 



#4 Noah4x4

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Posted 30 June 2020 - 04:57 PM

I struggled with this question when I migrated from an Atik Horizon camera to ZWO ASI294. Initially, I understated Gain and over exposed, partly because Atik graduates its gain measurements in units of 1 dB and ZWO in units of 0.1dB so "20" with Atik is "200" with ZWO.

 

However, there is a wonderful tool in Sharpcap called Smart Histogram.

 

I simply line up its dual green bars, and voila! Gain is accurately set! Then slide exposures until the left edge of the Smart Histogram curve is just inside the left edge of these green bars. Exposure is set. This process delivers the desired ratio with 90% accuracy. Tweaking it from there is simple.

 

You can try this in daylight too using a distant chimney. Exposures there will be much shorter than at night, but you will get a feel for this valuable tool that people rarely seem to talk about. But it works great for me.


Edited by Noah4x4, 30 June 2020 - 04:59 PM.



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