The two large open star clusters straddling the Serpens-Ophiuchus border and thus called the S-O Double Cluster. They are IC 4756 at left, a very large and scattered group, and NGC 6633 at right, a more concentrated group. Both are best seen with binoculars, and the field of the 200mm telephoto lens used here simulates a binocular field of view. This is a stack of 6 x 2-minute exposures with the 200mm lens at f/2.8 and Canon 6D MkII at ISO 800.
S-O Double Cluster consisting of: IC4756 in Serpens (at left) and NGC6633 in Ophiuchus (right), two good binocular objects. Thru Vixen 108DD astrograph at f/5 with Pentax 67 body and Fujichrome 400F slide film. 540mm focal length with about 7.5° wide field. Exposure about 20 minutes long taken in moonlight from rising waning Moon. Thus the blue sky which has been emphasized rather than neutralized. Taken July 2003 from home.
