Object Data: The Pleiades, M45, or 'Seven Sisters' has been revered since remote antiquity. It is the most famous of the galactic star clusters and well known to all observers through easy naked eye visibility of the seven brightest stars. The sparkling beauty of this jewel-like cluster remains the earliest celestial memory for many lovers of the night sky. Even more remarkable is the extent and structure of the beautiful reflection nebulosity which is shown to envelop the entire cluster in long exposure photographs.
Location: Southern France
Conditions: Calm, moderate dew, transparency=8, seeing=7-8
Optics: Astro-Physics 155 EDF f/7 with 4" focuser and integral field flattener working at f/7
Mount: AP 900 GTO on Portable Pier
Camera: SBIG ST-11K, SBIG LRGBC filter set, -20°C
Guiding: Integral ST-11K autoguider
Exposure: Single LRGB Seq: 14x 10 minutes; 3x 10 : 8 : 12 minutes (binned 2x2)
Processing: Image acquisition and initial processing using Maxim DL, subsequent processing in RegiStar and Photoshop.
Notes: This was my first completed image taken with the STL-11K. At this stage I had nothing empirical on which to base the RGB ratios, thus I used ratios I had seen in common use of 1 : 0.8 : 1.2. This proved inaccurate for my STL-11K and I compensated by using RGB weights in Maxim Color Combine. Subsequently I looked carefully at the STL-11K QE curve and RGB filter responses and decided that the SBIG recommended RGB ratio of 1 : 0.65 : 1 should be the most accurate. The results of subsequent image sets endorsed this.