Histogram sky brightness measurement

Discussion of using SharpCap for Deep Sky Imaging
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Topographic
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Histogram sky brightness measurement

#1

Post by Topographic »

Just a thought: if you are targeting one object for the night would there be any advantage to measuring whilst aiming at that part of the sky or am I missing something. By no means a rarity.

If not do you have a favourite location for measurement?
dbreit
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Re: Histogram sky brightness measurement

#2

Post by dbreit »

That's what I would do.. I am just a beginner though, so I could be wrong..

Derek
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admin
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Re: Histogram sky brightness measurement

#3

Post by admin »

Hi,

Yes, is usually best to measure the sky brightness in the vicinity of the object that you are going to be imaging. If you are imaging for a long time then the object may move enough that the sky brightness changes (for instance if you start imaging when the object is at an altitude of 45°, then it may move up towards the darker areas near the zenith as the night passes). If you think this is going to happen then consider measuring for the darkest area of the sky that the object will pass through.

Cheers, Robin
ausername
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Joined: Mon May 11, 2020 3:35 am

Re: Histogram sky brightness measurement

#4

Post by ausername »

I'm having trouble with the histogram exposure calculator. I'm using a ZWO ASI071MCPro which has been very reliable in SharpCap. I first set the selection 'box' on a dark sky area. When I press the 'measure sky' button, the gain and exposure time change, but then nothing happens even if I wait for ~15 minutes. I was able to get it to work in simulator mode. I'm wondering if there is a problem when the sky brightness is too high. I live in a Bortle 7 area and with this sky condition, perhaps there is no solution to the 5% noise constraint. Could that cause the program to hang? I do not get an error message.

The above is pure conjecture. Could I be doing something else wrong? I'm using the Pro version 3.2.6269.0 of SharpCap (March 16, 2020). Any suggestions would be welcome. Lastly, I think you have done a nice job on SharpCap and I like the fact that you are adding significant new features.
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Re: Histogram sky brightness measurement

#5

Post by admin »

Hi,

What should happen when you measure the sky background is that the gain should go pretty much to the maximum level (or close to it) and then the exposure should increase until the image becomes bright enough to measure. Some things that could potentially go wrong are that the exposure can become very long indeed (several minutes) or the camera could stop responding. Keeping an eye on the value of the exposure control and the frame progress and frame count in the status bar at the bottom should help you work out if either of these are happening.

Cheers, Robin
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