This image was obtained with a Canon 7D Mark II 20-megapixel digital camera and 300 mm f/2.8 L IS II lens at f/2.8 and ISO 1600. No dark frame subtraction, no flat fields. Tracking with an Astrotrac and no guiding. The 35 minutes total exposure (35 1-minute exposures).
This is a natural color image. The high dynamic range of astrophotos must be stretched to bring out the range of details the camera recorded. But the typical image stretch process loses color for brighter subjects (e.g. stars and the brighter parts of deep sky objects become whiter as they are made brighter). This image uses a new algorithm, rnc-color-stretch that does not lose color during the stretch. How do we know the colors are reasonable? The star colors can be checked against stellar photometry. The star color diversity is impressive in this region of the sky. Note the faint red stars, they have B-V > 2 (not the bright orange stars, which have B-V of 1 to about 2). The blue-white stars have B-V in the range of 0 to -0.5. The colors closely follow the color sequence in Table 1 at
Color of Stars. Solar-type stars have a B-V of 0.63 and appear close to white (daylight white balance).
More info at:
http://www.clarkvision.com/galleries/gallery.NEW/web/ic1848-soul-nebula.c08.13.2015.0J6A5447-91av35-t2-rs90,3.g-1300vs.htmlThe rnc-color-stretch is free open source and is described here:
http://www.clarkvision.com/articles/astrophotography-rnc-color-stretch/
Comments