Live Stacking Issues using New Image Train

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sandconp
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Joined: Thu May 31, 2018 7:48 pm

Live Stacking Issues using New Image Train

#1

Post by sandconp »

I have been using Live Stacking for a number of years generally without any issues. I usually use a Hyperstar which gives me a focal ratio of F/1.9. I decided to use a focal reducer and move the camera to the back of the telescope for galaxy season and I noticed that I had trouble getting enough star found for Sharpcap to perform a live stack. I normally set the gain at 120 for my ZWO camera and I had to increase the gain to 300+ for Sharpcap to find and align the stars.

Is this a problem when going from a F/1.9 to a F/6.3 where I have to increase the gain? I was using a ZWO OSC 183MC CMOS camera.
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admin
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Re: Live Stacking Issues using New Image Train

#2

Post by admin »

Hi,

going from f/1.9 to f/6.3 reduces the rate of light collection per pixel by a factor of about 11 - that means that you will have to do something to the camera controls to compensate for this - longer exposures or higher gain or a mixture of the two. You've done that by increasing the gain - approximately 18dB which is rougly 8x increase in brightness.

All sounds about right to me. If you find 300 gain too noisy then try doubling the exposure and dropping the gain back to about 240.

cheers,

Robin
sandconp
Posts: 81
Joined: Thu May 31, 2018 7:48 pm

Re: Live Stacking Issues using New Image Train

#3

Post by sandconp »

Robin,

I guess I should of used the Smart Histogram to figure out the gain, exposure length and number of exposures.

With my Hyperstar, I use a gain of 120 and it sound like I should of least doubled that.

That also explains why I had trouble using the Polar Alignment Tool using my new image train. I landed up using my guide scope to get a polar alignment and that worked fine.

Do you recommend using Smart Histogram in these situations and if so, do I need to run the sensor analysis on my camera first since I am running a newer Beta version since I last ran the Sensor Analysis on the non Beta Version?
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Re: Live Stacking Issues using New Image Train

#4

Post by admin »

Hi,

so there is no need to re-run the sensor analysis with the latest version - although I've made some changes to the analysis routines, they are all about making it more reliable and will not change the results.

You can certainly run the brain/smart histogram to get suggestions -they will involve longer exposures and/or higher gain because your sky background will be much darker due to the higher magnification.

cheers,

Robin
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