Image of the day 01/06/2015

This is an 8-panel mosaic taken with a f=500mm optics. Each panel contains an exposure time ranging from 1 hr to almost 2 hr. The total of the 8 panels is 10 hr 42 min.

Two wide field versions (Rev.B and Rev.C) are also uploaded. One of them (Rev.B) is taken with Nikon AIS ED 180mm/F2.8 at F4 and the other (Rev.C) is taken with Sigma 50mm/F1.4 Art at F3.3. The 180mm image is also an 8-panel mosaic, taken at the same time as the main 500mm mosaic, so the 180mm panels have large overlap with each other. The 50mm image is a stack of 15 3-min exposures.

The 50mm image were processed in PixInsight with its ABE function, to remove sky gradient in the central part of the image. (Gradient and imperfect flat fielding in the corners were not carefully processed.) Then the panels of the 180mm mosaic were registered and calibrated against the 50mm image, to remove sky gradient and to correct for imperfect flat fielding for a flat sky background. Then the panels of the high resolution 500mm mosaic were registered and calibrated against this 180mm mosaic, also to remove sky gradient and to improve background flatness. This 3-stage registration and background removal ensures a seamless mosaic, and also minimizes any sky gradient that may prevent the detection of very faint nebulas.

Remember to look at the full resolution image of the 500mm mosaic. Enjoy!

--- added in 2015/10: version D is a newer version. It contains additional 1.3 hr of data taken in 2015/10 in the lower-right quadrant to enhance the S/N there. The resultant image can therefore undergo stronger contrast stretch and saturation boost. The noise reduction scheme is also improved in this version.