Smart histogram and Live stacking quiestions

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bluesilver
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Joined: Mon Oct 05, 2020 12:51 am

Smart histogram and Live stacking quiestions

#1

Post by bluesilver »

Hi, I have done quiet a bit of research and also been watching quiet a few youtube videos on the Live Stacking in SharpCap, but nothing has really answered the question i am trying to find out.

So what i have been doing so far for imaging, is i have been using a different program to take my images and then i latter go a stack them and then process them.

But i am now more leaning towards SharpCap, as it has some very nice features going for it, I have SharpCap pro and the latest version of 4.0
I have just worked out how to use the smart histogram and the brain function to get an idea on how long of an exposure and gain for a certain object i want to image. ( but since then it has been cloudy now for about a month )

I have just came across this Live Stacking option,
Now every where i watch and read, people are adjusting the gain and exposure to get that white line in the histogram so that the line just starts in the bottom left hand corner and finishes just after the center line( the one on the camera panel ) Below is a screen shot for a youtube video to explain what i am rambling on about.
sharpcap.JPG
sharpcap.JPG (19.86 KiB) Viewed 582 times
So my question is, wouldn't you basically use the information that the brain function just calculated out for you ( gain and exposure ) instead of trying to adjust the gain and exposure levels to get that white line as it is in the image above?
Or is this two separate things?

I hope all that made sense on what i am trying to ask?
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admin
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Re: Smart histogram and Live stacking quiestions

#2

Post by admin »

Hi,

The smart histogram/brain is a much more scientific way of getting to the camera settings that work. The histogram 'rule of thumb' approach will do a decent job of making sure the first peak is separated from the left hand side to avoid black level clipping, and also will stop you from overexpsing the sky background to the point that would make stacking hard, but it doesn't really consider the optimium exposure length based on the camera noise characteristics, and it doesn't help you choose the appropriate gain based on your sky conditions and mount tracking capability.

With the histogram approach you could end up taking longer exposures than necessary and therefore struggling with guiding/tracking, or you could end up taking at too low a gain and therefore not be able to take long enough exposures to get the optimum results from your camera due to mount limitations.

cheers,

Robin
bluesilver
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Joined: Mon Oct 05, 2020 12:51 am

Re: Smart histogram and Live stacking quiestions

#3

Post by bluesilver »

Appreciate that reply and that bit of advice.
So, going from that, would i be correct in saying that you are better off using the brain function in the smart histogram to get a recommended gain and exposure setting, then if you decide to go with live stacking, just set the gain and exposure settings to those settings you just got from the brain function?

Am i on the right track with this line of thinking?
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Re: Smart histogram and Live stacking quiestions

#4

Post by admin »

Hi,

yes, that should usually work nicely.

Remember that you can go for longer exposures than recommended without any ill effect (unless you end up hitting the tracking limits of your mount and lose frames due to poor tracking/guiding). Sometimes this can help make more stars available for stacking/aligning, etc.

cheers,


Robin
calan
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Re: Smart histogram and Live stacking quiestions

#5

Post by calan »

I'll add my .02 cents...

After you've used the software a while with your own equipment and conditions, you'll get a pretty good ballpark idea of what works best. In order to get on target as quickly as possible, you'll want to have a dark library set up and ready to go...so concentrate your darks around what seems to be the most common recommendations, at certain gain ranges. (Unless you want to make new darks every time you change the gain and exposure to match "exactly" what the brain tells you).

I'm in a windy, light poluted sky, and I usually can't go longer than 5s exposures and expect to get many good frames...so I center around that, at gain ranges that change by 25. I focus on stacking lots (hundreds) of short high-quality frames, using the filters to weed out the bad ones. My rejection rate is usually more than 50%, but with short exposures and good filtering, it works.

With that said, I have darks ready to go at 2s, 3s, 5s, and 10s, at gains of 100, 150, 175, 200, 225, 250, and 300 (for 2s). I then just pick which ever gain and exposure combination is closest to what the brain recommends, using the longest exposure I expect to be able to hit reliably.

I only use the high gain for settings that are made to locate dim objects or center the scope on something; short exposures and usually with a bright screen stretch applied. My ideal imaging setting usually ends up at 5s, gain @ 150, unless I get an extremely rare night with no wind.
bluesilver
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Re: Smart histogram and Live stacking quiestions

#6

Post by bluesilver »

Appreciate all the advice, anything is appreciated.
My mount is the iOptron CEM120 and i use PHd2 multi star guiding.
I can get 5 minute exposures without any noticeable star trailing using PHd2, probably can go for longer, but just haven't tried

My skies here are pretty good, around bortle 2-3 range according to what the brain tells me.
The only issue is that we don't get many clear nights, so just trying to learn as much as i can to limit the amount of trial and error so to speak.

I am more for producing a good stacked result rather than just a finished image if that makes sense.
So maybe live stacking might not be for me, but i think there is a option in there that you can save each individual image and latter stack them, either in SharpCap or another program like deep sky stacker.
I think there was also options in there to automatically delete bad frames as they came in?
I will have to go back over and re read the manual a few times again to get the understanding of this.
But if i am correct, this alone will save heaps of time going back over each image.
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Re: Smart histogram and Live stacking quiestions

#7

Post by admin »

Hi,

yes, what you want to look at is the 'Raw Frames' saving option - you can choose to save None, All, Stacked Frames or All except when paused/dithering. You probably want to choose the Stacked Frames option, which will save those frames that SharpCap considers of good enough quality to stack (that pass any FWHM or brightness filter you have set up).

cheers,

Robin
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