Live Stacking not seeing stars

Discussions of Electronically Assisted Astronomy using the Live Stacking feature.
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allen456
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Joined: Wed Nov 10, 2021 8:02 pm

Live Stacking not seeing stars

#1

Post by allen456 »

I've tried to research this but too confusing. I had everything ready to go but couldn't get Live Stacking to work. Basically, it was saying that it couldn't align because it couldn't find any stars. Yeah, I had lots of stars. I've been over and over all the settings and can't see why. I did see something in the log that said "Mean FWHM is NaH" but I have no idea what this means other than it obviously has to do with focus. My focus was not great, generally between 4.5 and 4.9 was as good as I could get. I also tried the Bahtinov mask, which looked a little strange. I got nice symmetry on the spikes but the center seemed to have bumps all over it. I was shooting 16RAW at full resolution. I'm going to try again tonight and maybe drop down to 8 if it's still not working. But I could sure use some help.
allen456
Posts: 9
Joined: Wed Nov 10, 2021 8:02 pm

Re: Live Stacking not seeing stars

#2

Post by allen456 »

OK, I have stacking. I did it by ignoring what the Brain of the smart histogram was suggesting and by going strictly by the colored lines at the top of the Histo panel. I'm live stacking with flats but no darks, 25 sec exposure and a gain of 200. I'm getting a message that "Cannot calculate AWB because less than 5 stars in the saturation range 15% -> 95%". Again I have no idea of what this means although I suspect it may have to do with white balance. AWB may be Automatic White Balance but just a guess.

I was unable to balance the colors with the histogram-too much blue. I adjusted the white balance setting in the Image Controls and was able to balance this that way but now I have pinkish stars. The FWHM panel in Live Stack shows nothing but question marks at the bottom. I set Max FWHM all the way down to 1 and most of the frames are kept. So far I've got 100 keepers and 15 dropped. Brightness seems to track pretty well with the FWHM. But hey at least I'm stacking-that's progress.

One problem with learning Sharpcap is that many of the videos are out of date with the current version and hard to follow. Hope someone can recommend something good. I'm using an ASI294MC Pro and mainly chase DSOs.
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admin
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Re: Live Stacking not seeing stars

#3

Post by admin »

Hi,

if you are having trouble, the best thing to do is to watch the information in the alignment tab under the Live Stacking area (https://docs.sharpcap.co.uk/4.0/#Alignment%20Tab) - ideally you want somewhere between 30 and maybe 200-300 stars detected. Plenty of stars helps alignment and also white balance (to do the white balance it needs stars that are not too bright or too dim - that was the cause of the error you are seeing). Sometimes adjustments in the alignment tab help get the right number of stars detected, sometimes turning up the exposure/gain.

The smart histogram calculations focus on the best exposure lengths to get detail in the faint stuff, but in areas with few bright stars they can sometimes recommend too short an exposure (especially if you have quite a lot of light pollution). There is no harm in picking an exposure *longer* than the smart histogram suggestion - providing your mount guiding/tracking can handle it.

hope this helps,

Robin
allen456
Posts: 9
Joined: Wed Nov 10, 2021 8:02 pm

Re: Live Stacking not seeing stars

#4

Post by allen456 »

I did read that section of the manual and tried to incorporate it. Part of my trouble may have been my target selection. I was using a Canon 200mm f2.8 lens rather than a scope and I was shooting the entire Veil in one frame. This is an area where the density of the stars is pretty extreme. I got it working but had trouble with the color balance. I'm also having trouble with the focus assist tools-the numbers say I'm focused but my eye assures me that I'm not. I stacked the Veil but wasn't happy with it. My stars were bloated and pinkish. After that I switched to M31 and had much better luck. I used a Bahtinov mask and just my eyes and definitely got better focus. I also dropped my exposure way down to 4 secs, gain 200. This put me in the favorable area of the colored lines at the top of the histo panel (even though it was far from what the Measure recommended) and my images were the best so far. I still needed a lot of adjustment for color balance. I was watching my screen as well as the histogram and accept a view where the red was a little to the left and the blue a little to the right of the center which had the green and luminance aligned. Is this an acceptable practice? If you're having trouble aligning your colors, is it ok to adjust the white balance with the Image Controls? Does AWB mean Auto White Balance in the error message that I previously got? What does Mean FWHM is NaN mean? My goal here has been to learn how to use lucky imaging in Live Stack.
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Re: Live Stacking not seeing stars

#5

Post by admin »

Hi,

so on the subject of the alignment issues, the best way forward is probably to send me a couple of unprocessed frames of the target so I can tinker with them and see what needs to be done.

On the white balance, you have two ways to adjust - one in the image controls on the right, which tends to cause the adjustments to be applied before the image data gets to SharpCap, and the other is in the live stacking section - in that case the adjustments are applied to the final stacked image before displaying it. Personally I prefer to leave the image controls alone and use the live stacking adjustments, as the changes are not 'locked in' to the image data that way - if you decide they are wrong you can tweak more. Others get great results from adjusting the white balance in the image controls though.

And yes, AWB does stand for Auto White Balance.

cheers,

Robin
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