Just completed the first two night of live stacking with SharpCap, using ZWO ASI294MC camera and Alt/Az ServoCAT driven 18" f/4 dobsonian telescope. Really liking the software and amazed a cheapish Windows 11 tablet from Amazon can deal with intensive imaging tasks. Having a separate side-mounted 11" monitor for "Two monitor" mode also works, nice to have a dedicated screen for the camera image..... Couple of questions:
1) For target finding, I used "Live View", set with short exposure eg 0.5s, high gain. The mini-histogram tool was the key thing to make this this work, clicking the lightening bolt to auto-stretch. This was used to center the target using the ServoCAT handpad slew arrow buttons, then click "Live Stack" on SharpCap. Instead of the mini-histogram tool, the equivalent of the live stacking histogram window, with its enhanced functionality/ usability would be better to facilitate target finding in "Live View" eg auto-colour lightening button, log and zoom buttons and easier to set the black and grey points with the larger display area offered by being on the "work area" panel (bearing in mind the size of a tablet screen). Suggestions ?
2) Push to Assistant. Seems to work nicely. One issue: the "Move Telescope (Alt/Az)" section at the bottom was blank. It was only showing movements for an equitorial mount. Couldn't find anywhere in the software to tell SharpCap my scope is Alt/Az. Ideally for a Alt/Az driven dob you need prompts from SharpCap to suggest which arrows to press on the ServoCAT handpad to slew the telescope (left/right and up/down)
Will need to address vignetting which was marked after live stacking. Pushing my non-imaging scope from f/4 to f/3 with the Starizona 0.75x reducer/ Newtonian corrector, clearly greatly curtails the fully illuminated image circle, as predicted by Mel Bartell's calculator. May need to dial back to f/4 and/or plan taking flats (maybe not trivial for 457mm of aperture). Wide FoV with f/3 really nice though and stars tack-sharp to the edge.
Beginner Questions
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Re: Beginner Questions
Hi,
glad to hear that you are enjoying using SharpCap and that it's helping you find and image targets.
The mini histogram is fairly limited largely because of the size - there's not really much space to add finer adjustments or more functionality there, and making it bigger would impact on the other controls for the camera that you want to be able to see as well. Even an auto colour balance button would be a bit of a problem, as there is no room to add manual adjustments to fine tune if the auto balance gets it wrong.
The 'lightning bolt' auto adjust is a key feature as you found out for helping find targets. The 'lock' is fairly handy too - that automatically re-stretches every second or so as if you were constantly hitting the lightning bolt, so it's good if the brightness changes as you move around, etc.
For the push-to calculations, the Alt/Az adjustments can only be calculated if SharpCap knows your latitude and longitude, which by default it doesn't. Since you aren't using an ASCOM driver for your mount you can't set the lat/long that way, but you can set it in the 'Polar Alignment' settings and those co-ordinates should also get used by the PushTo assistant to give you alt/az offset values.
cheers,
Robin
glad to hear that you are enjoying using SharpCap and that it's helping you find and image targets.
The mini histogram is fairly limited largely because of the size - there's not really much space to add finer adjustments or more functionality there, and making it bigger would impact on the other controls for the camera that you want to be able to see as well. Even an auto colour balance button would be a bit of a problem, as there is no room to add manual adjustments to fine tune if the auto balance gets it wrong.
The 'lightning bolt' auto adjust is a key feature as you found out for helping find targets. The 'lock' is fairly handy too - that automatically re-stretches every second or so as if you were constantly hitting the lightning bolt, so it's good if the brightness changes as you move around, etc.
For the push-to calculations, the Alt/Az adjustments can only be calculated if SharpCap knows your latitude and longitude, which by default it doesn't. Since you aren't using an ASCOM driver for your mount you can't set the lat/long that way, but you can set it in the 'Polar Alignment' settings and those co-ordinates should also get used by the PushTo assistant to give you alt/az offset values.
cheers,
Robin
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jonstarrysky
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Re: Beginner Questions
Thanks Robin,
Re the mini histogram I guess a work-around could be to go straight to Live Stack mode for target finding and select View_Individual Frames. When the target is centered switch to View_Stack, then click Clear under the Actions group. Sure its giving the PC an unnecessary workout (redundant alignments) but should work ?
Re the mini histogram I guess a work-around could be to go straight to Live Stack mode for target finding and select View_Individual Frames. When the target is centered switch to View_Stack, then click Clear under the Actions group. Sure its giving the PC an unnecessary workout (redundant alignments) but should work ?
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Re: Beginner Questions
Hi,
I don't think that the histogram/colour adjustments in the live stacking apply when you are viewing the raw frames, so I'm afraid I don't think it would work.
It's worth noting that you can use some of the tricks for fine adjustment of the live stacking histogram stretch on the mini histogram too - that is holding shift while dragging the black/mid/white level lines and also dragging them with the mouse above/below the control (see https://docs.sharpcap.co.uk/4.1/#Making ... 0Histogram)
cheers,
Robin
I don't think that the histogram/colour adjustments in the live stacking apply when you are viewing the raw frames, so I'm afraid I don't think it would work.
It's worth noting that you can use some of the tricks for fine adjustment of the live stacking histogram stretch on the mini histogram too - that is holding shift while dragging the black/mid/white level lines and also dragging them with the mouse above/below the control (see https://docs.sharpcap.co.uk/4.1/#Making ... 0Histogram)
cheers,
Robin
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jonstarrysky
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Re: Beginner Questions
Couple of questions following a few further nights of getting to grips with SharpCap & EAA with a big dob (FL 1833mm, f/4, Bortle ~5) & the ASI294MC..... Notably filtering-out bad frames with star trails
One of the main initial tasks is to learn (theoretical and empirical) optimal settings for stacking DSOs with this setup.
Tracking is not overly smooth with this scope, being a dob mount with ServoCAT. Am finding 8 second frames is touch-and-go. Sometimes is OK other times not, in which case stars look like short or squiggly lines, even after clearing the stack and starting over. In these cases switching to 4 second is much more reliable, as if some sort of threshold is being passed, kind of odd. The brain button was suggesting 15 seconds (the longest I let it choose) with minimum gain that triggers HGC (gain 120), so would be good to troubleshoot longer exposures of 8 seconds or more. I'm filtering with FWHM and brightness, somewhat stringently (discards at least half of the frames), perhaps being key to some of the nice results so far at 4s. Will FWHM be filtering frames where the tracking is bad, turning stars into lines ?? I assume its doing so at 4s at least, I've gone up to 10 min stacks (total integration time) with stars looking sharp. Maybe something in the FWHM settings is meaning at 8s the star-trail pixel count is too high to filter ?? Nb. the images are oversampled at 0.52' per pixel.
Playing about with gain (testing at 120, 200, 300) in terms of the smart histogram, the main peak is always in the green zone of the top bar, even at 4s. I am surprised at what's possible by stacking short 4s exposures TBH, and how increasing gain maybe doesn't add much to the end result, despite in absolute terms the signal being much brighter. Stacks of easy DSOs look impressive at 3 min total integration time, at which point field rotation black-edges sometimes creep in, so this may be a sweet-spot, and going up to 10 min total integration for feinter/ smaller DSOs and cropping later.
Perhaps will look at binning again, initial tests were confusing, and maybe binning as a possible source of issues eg the debayering etc. Hardware vs Software etc. Seems a lack of precedent on the web for binning on the ASI294MC colour camera. A lot of comments on what it *should* do.... not so much "I did bin-x and observed better/worse/same results vs un-binned".
One of the main initial tasks is to learn (theoretical and empirical) optimal settings for stacking DSOs with this setup.
Tracking is not overly smooth with this scope, being a dob mount with ServoCAT. Am finding 8 second frames is touch-and-go. Sometimes is OK other times not, in which case stars look like short or squiggly lines, even after clearing the stack and starting over. In these cases switching to 4 second is much more reliable, as if some sort of threshold is being passed, kind of odd. The brain button was suggesting 15 seconds (the longest I let it choose) with minimum gain that triggers HGC (gain 120), so would be good to troubleshoot longer exposures of 8 seconds or more. I'm filtering with FWHM and brightness, somewhat stringently (discards at least half of the frames), perhaps being key to some of the nice results so far at 4s. Will FWHM be filtering frames where the tracking is bad, turning stars into lines ?? I assume its doing so at 4s at least, I've gone up to 10 min stacks (total integration time) with stars looking sharp. Maybe something in the FWHM settings is meaning at 8s the star-trail pixel count is too high to filter ?? Nb. the images are oversampled at 0.52' per pixel.
Playing about with gain (testing at 120, 200, 300) in terms of the smart histogram, the main peak is always in the green zone of the top bar, even at 4s. I am surprised at what's possible by stacking short 4s exposures TBH, and how increasing gain maybe doesn't add much to the end result, despite in absolute terms the signal being much brighter. Stacks of easy DSOs look impressive at 3 min total integration time, at which point field rotation black-edges sometimes creep in, so this may be a sweet-spot, and going up to 10 min total integration for feinter/ smaller DSOs and cropping later.
Perhaps will look at binning again, initial tests were confusing, and maybe binning as a possible source of issues eg the debayering etc. Hardware vs Software etc. Seems a lack of precedent on the web for binning on the ASI294MC colour camera. A lot of comments on what it *should* do.... not so much "I did bin-x and observed better/worse/same results vs un-binned".
Last edited by jonstarrysky on Wed Aug 07, 2024 12:38 pm, edited 1 time in total.
Re: Beginner Questions
Jon,
Exposure length is primarily a function of sky brightness and sensor read noise. Therefore, unless you've got super dark skies and a noisy camera, there is no need for 10-minute exposures.
Just experiment! If the Brain says 15 seconds but your mount wants 4 seconds, just try it. Capture a 20-minute stack of 4-second exposures and see how that compares to a 20-minute stack of 8-second exposures. You may find that 4-second exposures work well enough. It's all a game of give-and-take.
Brian
Exposure length is primarily a function of sky brightness and sensor read noise. Therefore, unless you've got super dark skies and a noisy camera, there is no need for 10-minute exposures.
Just experiment! If the Brain says 15 seconds but your mount wants 4 seconds, just try it. Capture a 20-minute stack of 4-second exposures and see how that compares to a 20-minute stack of 8-second exposures. You may find that 4-second exposures work well enough. It's all a game of give-and-take.
Brian
Re: Beginner Questions
Jon,
Here is a good example of the power of experimentation:
viewtopic.php?t=2313
The Brain said I needed 80 seconds exposure with my green filter but I chose 8 seconds. Sure I had to capture A LOT of frames to achieve a relatively noise-free image. However, if I followed the Brain's recommendation I could have achieved the same quality in far less time but that wasn't my goal. I wanted to prove to myself that I do have flexibility.
Brian
Here is a good example of the power of experimentation:
viewtopic.php?t=2313
The Brain said I needed 80 seconds exposure with my green filter but I chose 8 seconds. Sure I had to capture A LOT of frames to achieve a relatively noise-free image. However, if I followed the Brain's recommendation I could have achieved the same quality in far less time but that wasn't my goal. I wanted to prove to myself that I do have flexibility.
Brian
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Re: Beginner Questions
Hi,
just to note that the filtering on FWHM can partly help deal with smeared frames due to tracking problems, but not entirely eliminate them. There are all sorts of possibilities of what you might get in the image from stars that are streaks if the tracking is gradually shifting during the frame to duplicated stars if the tracking shifts fairly rapidly part way through but is otherwise decent. Not all of those get picked up by the FWHM filter.
As oopfan says, there is a lot to be said for trying out the various options and seeing how they work. Being able to keep 75% of 4s frames might well do better than only keeping 50% of 8s frames, even if 4s is below the recommended exposure level, since the total exposure time will build up more quickly in the 4s case.
Higher gain only really helps by reducing the read noise, so it is important to get from LCG to HCG and some impact just beyond that point, but if you look at the read noise vs gain graph, it soon becomes fairly flat, so the further improvements due to increasing gain become pretty marginal.
thanks,
Robin
just to note that the filtering on FWHM can partly help deal with smeared frames due to tracking problems, but not entirely eliminate them. There are all sorts of possibilities of what you might get in the image from stars that are streaks if the tracking is gradually shifting during the frame to duplicated stars if the tracking shifts fairly rapidly part way through but is otherwise decent. Not all of those get picked up by the FWHM filter.
As oopfan says, there is a lot to be said for trying out the various options and seeing how they work. Being able to keep 75% of 4s frames might well do better than only keeping 50% of 8s frames, even if 4s is below the recommended exposure level, since the total exposure time will build up more quickly in the 4s case.
Higher gain only really helps by reducing the read noise, so it is important to get from LCG to HCG and some impact just beyond that point, but if you look at the read noise vs gain graph, it soon becomes fairly flat, so the further improvements due to increasing gain become pretty marginal.
thanks,
Robin
Re: Beginner Questions
Jon,
The object I imaged was a star cluster, therefore I was able to use 8-second exposures instead of the Brain-recommended 80 seconds. However, if I was imaging a faint nebula my choice of exposure would have been poor. The ratio of 80sec to 8sec is 10:1. In your case Jon, going from 15sec to 4sec is a 4:1 ratio, therefore my gut feeling is you've got a good chance of imaging galaxies. Give it a try! What have you got to lose? It's better than going out and buying a new rig for thousands of dollars. My advice is to begin with the large bright galaxies and nebulae, then work towards smaller and fainter galaxies. That way you'll be thrilled with your success from the start. Having several successes under your belt, then you can choose fainter targets. That's when you learn how to deal with disappointment. Don't forget to post your images on the forum!
Brian
The object I imaged was a star cluster, therefore I was able to use 8-second exposures instead of the Brain-recommended 80 seconds. However, if I was imaging a faint nebula my choice of exposure would have been poor. The ratio of 80sec to 8sec is 10:1. In your case Jon, going from 15sec to 4sec is a 4:1 ratio, therefore my gut feeling is you've got a good chance of imaging galaxies. Give it a try! What have you got to lose? It's better than going out and buying a new rig for thousands of dollars. My advice is to begin with the large bright galaxies and nebulae, then work towards smaller and fainter galaxies. That way you'll be thrilled with your success from the start. Having several successes under your belt, then you can choose fainter targets. That's when you learn how to deal with disappointment. Don't forget to post your images on the forum!
Brian
Re: Beginner Questions
Jon,
I do eaa with a 12” dob with nexus at 1250 fl. Because my scope is full manual I bought a equatorial platform. To find the longest sub exposure I could take I leave sc in live mode and using a high gain increase exposure looking at each individual frame,until stars elongate. This will give you a good idea of mounts tracking ability.
I do eaa with a 12” dob with nexus at 1250 fl. Because my scope is full manual I bought a equatorial platform. To find the longest sub exposure I could take I leave sc in live mode and using a high gain increase exposure looking at each individual frame,until stars elongate. This will give you a good idea of mounts tracking ability.