Why Does Sharpcap Take So Long to Stack an Image?

[RIAstronomer]

I have been having an occasional issue where I'm using Livestack and it will add a recently completed frame to the stack immediately upon completion of the exposure and then start the next exposure, but on the next frame Sharpcap can end up taking up to 2 minutes or more after the 20 second exposure to add the next frame to the stack before starting the next exposure. Does anyone know why this happens and if so, is there a fix for it? I have had nights where this doesn't happen, but the last three times I set up in the back yard, I ran into this problem on every object I imaged. I cannot find anything in the manual that seems to address this. Most of my imaging is done in Bortle 7/8 skies, and my most recent exposures were shooting galaxies at 20 seconds per frame with a QHY 290m camera. This problem has also happened under Bortle 4 skies (the darkest skies available to me), so I'm not entirely convinced that city observing is the problem. Further, I'm seeing plenty of stars in the images.

I have tried adjusting various controls, but nothing seems to address this. Last night was particularly troubling since my guests were wondering why it was taking up to 10 minutes or more to capture a 5 minute stack (I was using electronically assisted astronomy and trying to shoot galaxies using 20 second exposures for a total of 5 minutes). The one or two objects where this issue wasn't too bad were OK. They enjoyed watching the image gradually improve as the stack count increased, but many objects were requiring 10 minutes or more. I'd like to do this at one of my club's next public outings, but I know that the general public isn't going to have the patience to wait 3 minutes for even the first image to finally show up (this happened three times last night).

What was particularly perplexing is that this happened even when I tried to take a dark using 20 second frames. It frequently took anywhere from 30 to 200 seconds beyond the 20 second frame before a dark was actually captured. I finally gave up trying to use the dark frame tool because of this.

Thanks,

Ken

[admin]

Hi Ken,

it sounds like you are having issues where your camera is not consistently delivering frames to SharpCap - this would explain the fact that you are seeing the same sort of problem across various different features like capturing a dark and live stacking.

If you set up 20s exposures without any other features enabled, you can watch the frame count (bottom left) to see if it is incrementing regularly every 20s or so, or if there are long pauses without any increment (I'm suspecting the latter).

It's probably worth checking the 'troubleshooting USB issues' thread - viewtopic.php?f=18&t=349&p=1556#p1556 - to see if any of the suggestions there help. Intermittent problems in getting frames are often related to USB issues. Also you could try the 'Force Still Mode' option for your camera (in the camera settings) if available. This pushes QHY cameras into using their still capture mode, which can be more reliable for longer exposures.

cheers,

Robin