M33 galaxy (the Triangulum "pinwheel" galaxy) obtained through wideband LRGB filters and a narrowband H alpha filter, total exposure of 26,5 hours. Image shown at 66% of size

Equipment: Vixen VC200L scope. ASA DDM85 mount. SBIG STL11000 camera. Filters: Luminance, Blue, Red, Green and H alpha.

Location: Pozuelo (Madrid suburbs)

Date: September and October 2011

Exposures: 120x5 min Luminance, 7x15 minutes Blue, 7X15min Green, 8X15 min Red and 11x60 min Halpha

Each subexposure was guided with a home-made off-axis guider, with long (over 10 seconds) autoguider exposures and "pulse guiding".

The spider vanes of the VC200L scope have been thinned to diminish diffraction artifacts, avoiding a square stasr appearance.

The H alpha channel was employed to enhance the red channel (merged with the red channel) and the blue channel (multiplied by 0.15 and merged with the blue channel)

Strong color gradients were originally present in the images due to the very high light pollution in Madrid suburbs. To eliminate these gradients as possible, Pixinsight function DBE (dynamic background extraction) was employed.