SharpCap Forums

Hi!
I've got some troubles photographing Deepsky objects. I am using feature tracking with surface features at 10s exposures because otherwise after approximately an hour, the stars are out of the field of view. I'm shooting with a ZWO ASI 715MC (planetary camera) and a Skywatcher Explorer 150P (750mm focal length), so my field of view is only about a half degree and one pixel is equal to 0,4 arc seconds. Nevertheless, the camera is able to take 30s exposures and the stars are perfectly round. I don't have a guide scope and a guide camera but I'm convinced that Sharp cap is able to track the stars well and that worked with feature tracking. More than 5 hours, feature tracking tracked the mount down to the pixel and the result: Walking noise. Because of that I have to dither. But I don't have a guiding system, so next time I'd like to try it with the advanced sequence editor where you can dither. But I'm not sure if feature tracking will work while the advanced sequence editor is running because there is no block "start feature tracking". Thanks for helping!

Hi,

you are kind of fighting against the way that things are designed to work in SharpCap...

The real starting point here is that the feature tracking is not really designed to do the sort of tracking that you are using it for - it's designed for keeping a view of the sun, moon or a planet roughly steady, rather than keeping a star field in view over long periods. Because of this, it's not designed for interaction with dithering, and if you did persuade SharpCap to try to dither while it was active, it would happily try to put the image back to the original position, cancelling out the dither...

There are alternative approaches in SharpCap that might work better - for instance, if you use live stacking then you can configure it to dither periodically (including a dither based on random, small, mount movements that doesn't need a guide camera). You can also configure live stacking to recenter the view using plate solving if the image drifts by more than a set number of pixels. A combination of those would probably achieve the same sort of result of keeping the same area in view over longer periods, but the dithering should help with the walking noise. You can set up live stacking to save the unprocessed frames fromt he camera for later manual processing if you want, just treating live stacking as a convenient way to handle the dithering/re-centering while capturing.

It's also worth considering dark frames, or at the very least hot/cold pixel correction , as the most prominent walking noise comes from hot/cold (warm/cool) pixels, so it can help to reduce that variability in the source images.

cheers,

Robin

Hi Robin,
thanks for your answer. I think I'll try to photograph these objects using the advanced sequence editor (platesolving and move to target).

Kind regards,
SternwarteOrion.

Hi,
I tried keeping the image centered using the advanced sequence editor (plate solve, sync and re-goto) but that didn't work.
Platesolving failed and the sequence was aborted. Instead of 5 hours exposure time, I got 1 hour. Are there any alternatives for platesolving?
Kind regards,
SternwarteOrion.

Hi,

SharpCap has the ability to work with a number of plate solving programs, including an inbuilt solver and tools like Astap, Astrotortilla, ASPS, Ansvr, PlateSolve3, etc.

It's worth checking out a typical star field with the plate solving program you intend to use as there may be settings that need to be adjusted. There are also field-of-view limitations on some plate solving tools (particularly if you only installer the smaller plate solving databases).

cheers,

Robin