This is a continuing experiment in urban imaging taken from mag 3 skies. The ISO was reduced to extend the exposure of each sub-frame to three minutes. It is also a guiding test of a new Celestron Nexguide stand alone autoguider. The guider was locked on a 5'th to 6'th magnitude guide star using a 60 mm guide scope.

Object M3 Object RA 13:42.2 Dec +28:23
Exposure 42 minutes (14 X 3 minutes)
ISO 400 (This image was made from urban skies where third magnitude stars were barely visible. Lower ISO was used to increase the sub-exposure integration time)
Camera Canon 350D DSLR
Optics 8" f/4 Schmidt Newtonian Telescope
Location Bedford, Nova Scotia

Calibration, stacking, background noise reduction done with Images Plus . Two images created using the digital development function of Images Plus. One with a very slight stretch to preserve the core and another with a more aggressive stretch to make the dimmer outer cluster stars visible. The two images were combined using an LMS technique in Paint Shop Pro. The background was corrected in Paint Shop Pro using a subtractive layer background correction . A masked noise reduction was applied to reduce the background noise further. Finally a slight curve stretch was applied in Paint Shop Pro .