This may not be a question about CHDK as such, but rather about what happened when it interacted with a particular camera. With 60-second exposures, flare-like artifacts appear in the left corners but not in the right corners This can be seen both in the image and in the dark frame:
Subtracting the dark frame removes most of this artifact, but it is severe enough to be a major nuisance, as some degradation of image quality at the corners is noticeable, and it were better to solve the underlying problem.
-CHDK version was 1.4.0.
-The script used was meteor2.lua; thie frame was part of a series of 40.
-The ISO was 200 and the aperture was set to f/2.8 with the ND out.
-The scene was much dimmer than the top picture suggests; the foreground was almost invisible without a flashlight.
-The display backlight illuminated briefly between frames; otherwise, the only light on the camera was a flashing orange LED on the rear and a blue LED which illuminated briefly between frames.
-The effect does not appear when operating the camera in the usual single-shot mode, even at ISO 1600.
-What is this?