Simeis 57 (The Propeller)

During the night of 25-26 August 2007, I used my TMB 115/800 APO refractor to image Simeis 57 with my ST-10XME + Astronomik H-alfa filter, the result is shown below. During the nights of 26-27 August and 29-30 August I also imaged the object with respectively an Astronomik O3 and S2 filter. Exposure for each filter was 2 hours, the narrow-band image is below the H-Alfa image (I used the CFHT palette: H-alfa = R, O3 = G and S2 = B). The O3 image didn't contain almost any nebulosity while the H-alfa image contributes most of it. Narrow-band imaging needs a lot more exposure time than this to obtain noise free images...