M-17 taken with an AP 140 F7.5 Starfire EDF Astrograph Refractor with 4" focuser.
The instrument was working at F5.7 with the 155TCC Telecompressor Corrector.
STL11000 camera with Baader 50.8 mm Unmounted Narrow Band CCD Imaging Filters for STL Cameras.
Exposure: 2 x 20 minutes H-alpha and 2 x 20 minute O3. Red = H-a, green = 1/2(Ha + O3), blue = O3.
Although reduced to a manageable file size, this image is the full frame of the large STL11000 CCD chip.
Note the round, pinpoint stars at all four corners!
Image by Roland Christen.