NGC 6905 (Delphinus)

The planetary nebula NGC 6905 ("Blue Flash Nebula") in the constellation Delphinus. In Herschel 400 Observing Guide, Steve O'Meara calls NGC 6905 the "Caged Spirit Nebula": When looking through a telescope, the nebula seems to bounce between a triangle of 11th and 12th magnitude stars. When viewed directly, the small and bright spherical center of the nebula can be seen. When viewed using averted vision (by not looking at the object directly, but looking a little off to the side of it, while continuing to concentrate on the object), the outer parts of the nebula become visible. When switching between direct and averted vision, the nebula seems to bounce off the adjacent stars. NGC 6905 is 7,500 light-years from Earth, has a 14.0 mag bright central star and was discovered by William Herschel in 1784 (source: Wikipedia).

Twenty-two 3-minute exposures (66 minutes total exposure) at ISO 800, taken on September 15, 2018, were added for this shot with the DeepSkyStacker software and the final image processing was done in Photoshop.

Equipment: Canon EOS 450D Baader modified camera, TeleVue Paracorr Type II coma corrector, 16" f/4.5 "Ninja" dobsonian telescope riding on a dual-axis Tom Osypowski equatorial platform, Lacerta MGEN autoguider, Lacerta off axis system (field of view comparison: image of the moon with the same equipment).