Given that we just had to change a bent propeller that lost a battle with a rock, this seemed an appropriate summer target. Located in the constellation Cygnus, this emission nebula is properly known as Simeis 57, and is part of the Cygnus X complex. The propeller itself is described by the designation DWB 111 and 119. In this image orientation, the lower left propeller blade is DWB 119 (northern blade), and the upper right blade is DWB 111 (southern blade). A great reference for these different components can be found at
http://www.distant-lights.at/simeis57_hubble-2015_08_31.htm. Processing this target in narrowband was quite challenging given the strong and nearly symmetrical Ha and Sii signal and very faint OIII signal. After previewing a variety of possible narrowband combinations on Dylan O'Donnell's very useful Online Narrowband RGB Combination Preview Tool (
https://www.bintel.com.au/narrowband-preview-tool/), the starting point for this image was the classic Hubble palate of SHO. However, this resulted in an overtly green and washed out image, so great liberties were taken modifying the channels to try and bring out the blue a bit more. The false color space of narrowband imaging is a jarring change from the careful color calibration and fidelity to "reality" represented in LRGB imaging. However, this is a much more interesting target in Narrowband than the LRGB counterpart, at least in my two processing workflows.
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