I have been building some mosaics using the Pier 14 widefield rig. This has a full-frame mono camera and an FSQ106 reduced to 387mm FL so a 5.41° x 3.51° FOV. The edges of the frame are a bit iffy in terms of coma and other defects, but it is great to have so wide a field to operate in.
I have just completed a three-pane mosaic of the regions from the Clamshell to the Pelican nebulas, narrowband in SHO palette. Most of my problems were struggling to balance up the three panels to avoid visible joins. But whilst pixel-peeping to see if I was having any success (always a dangerous game) I noticed some misalignment issues.
This is the edge of the frame where a couple of panels overlap:
Clearly poor alignment and/or distortion.
Take an image at the same scale and column position, but from the centre of the frame and you get this:
Not the same problem at all.
My process was:
- Get all the 9 frames calibrated and stacked[/*]DynamicBackgroundExtraction on each frame[/*]Combine the frames for each filter into a mono mosaic:[list=1]DNA LInear Fit two outer panels for each filter to the centre panel (strongest signal)[/*]Image solve each panel[/*]Run MosaicByCoordinates for the three panels using script defaults[/*]GradientMergeMosaic using Overlay combination method with increased shrink and feather radius to suppress seams.[/*]
- Calibrate and stack all 9 frames[/*]DynamicBackgroundExtraction on each frame[/*]StarAlign filters for each frame using Thin Plate Splines and Distortion Correction[list=1]DNA LInear Fit two outer panels for each filter to the centre panel (strongest signal)[/*]Image solve each panel[/*]Run MosaicByCoordinates for the three panels using script defaults[/*]Run TrimMosaicTile script to clean up edges (necessary for PhotometricMosaic script)[/*]Run PhotometricMosaic twice using script defaults (join two panels then add the third)[/*]