Bug 398198

Summary: Mount tracking while taking flats in "Wall" mode
Product: [Applications] kstars Reporter: TallFurryMan <eric.dejouhanet>
Component: generalAssignee: Jasem Mutlaq <mutlaqja>
Status: RESOLVED FIXED    
Severity: normal    
Priority: NOR    
Version First Reported In: 2.9.8   
Target Milestone: ---   
Platform: Other   
OS: Linux   
Latest Commit: Version Fixed/Implemented In:
Sentry Crash Report:

Description TallFurryMan 2018-09-03 12:15:05 UTC 
When capturing flats in "Wall" mode with AltAz coordinates, mount is left to track after slewing. Mount must not track while taking flats.

In the case of a real flat panel hanging on a wall, the mount may not have the time to drift away by the time flat frames are taken. In this (intended) use case, the problem is there but the symptom doesn't appear.

However while option "Dawn/Dusk" is not currently implemented in Ekos, it is nonetheless possible to take dawn/dusk flats in "Wall" mode and use a particular area of the sky as light source.

Because the mount is tracking while in this mode, stars that may appear during capture will remain at the same place on the frame, defeating the purpose of the flat.

Side note about the current implementation of exposure calibration in the "Wall" mode: at a certain point in the dawn/dusk transition interval, the ADU calculation is not able to follow the speed at which the sky luminosity changes. Exposure adjustment is indeed calibrated for a static light source.
Comment 1 Jasem Mutlaq 2018-09-03 17:16:15 UTC 
Dusk/Dawn flats are not enabled right now because there is no implementation for them in KStars. It was there just as a future TODO. IMO, having artificial light source is a lot more reliable.
Comment 2 TallFurryMan 2018-09-03 19:10:46 UTC 
Agreed, this ticket only applies to the "Wall" mode.

Thinking about it, I even wonder if tracking would actually improve the flat quality. But, well capturing something static is better done without moving I suppose.

About dawn/dusk frames, if the ADU calibration curve is added to a simple linear function with a customizable slope to cater for the decreasing or increasing luminosity, and tracking is stopped too, we get our dawn/dusk flat capture feature.