NGC 2158: This cluster is more often observed as the fainter, much smaller cluster right next to the prominent M35 open cluster in Gemini. This cluster is estimated to be over 1 billion years old.
Right Ascension: 6 hrs 7.5 min
Declination: 24° 6'
Apparent Magnitude: 8.6
Date: April 2010
Telescope: Meade 16" Schmidt Cassegrain with f6.3 reducer
Camera: SBIG ST-10XE
Guiding: Meade 5" refractor/DSI Pro/PHD
Exposure: R:V:B: 10 minutes each in 2 minute subframes
The camera was at -30°C.
Processing Notes: Data acquisition with CCDSoft. Reduced and aligned in CCDStack. Subs combined in Sigma Beta. RVB combined in AstroArt with a ratio of ~1:2:4 as determined by the auto-white balance feature. Image saved as a TIFF for import into Photoshop. Adjusted curves and levels, and added a Gaussian blur on the dim areas. Sharpening on bright areas. Slight, faded, minimum filter to reduce star sizes.
Additional Comments: The R filter in the photometric set is significantly sensitive in IR, so many of the cooler stars show up in this image as very red stars, where they might not be seen at all with a "photographic" red filter. The other significant difference in color balance is that [OIII] is detected more in the V ("visible", or green) filter than the B, or "blue" filter.