M74: This nice, symmetric, face-on, "Grand Design" spiral galaxy is one of the dimmest galaxies in the Messier catalog. It is found in the constellation Pisces.
Right Ascension: 1h 36m
Declination: 15° 47'
Apparent Magnitude: 10
Date: October 2010
Telescope: Meade 16" Schmidt Cassegrain with f6.3 reducer (used at ~ f6.1)
Camera: SBIG ST-10XE
Luminance Guiding: AO-8
RGB Guiding: PHD, DSI Pro, Meade 5"
Exposure: L: 25x10 minutes, binned 1x1
RG: 10x5 minutes, B: 9x5 minutes, binned 2x2
The camera was at -35°
Processing Notes: Data acquisition with CCDSoft. Reduced and aligned in CCDStack and combined with Sigma combine. Arcsine stretch import of L into Photoshop. Adjusted curves and levels. Increased contrast via a highpass filter overlay layer. Slight blur on the dim areas and sharpening on non-star bright areas. Minimize filter on the stars. RGB combined in AstroArt at 1:1.05:1.65 ratio. Adjusted curves and levels, and reduced noise of RGB. L was combined with RGB using three layers: Luminance on the bottom; RGB as a multiply(30%) layer; and RGB as a color layer on top. Final color adjustment and tweak in Photoshop.
Scale: 0.52"/pixel on highest resolution
Links to images of this object on other sites:
Additional Comments: This is the first image after "loosening" the primary mirror. This allows the mirror to "flop" slightly, which is worse for guiding using PHD, but the through-the-lens guiding for the luminance channel using the AO-8 compensates for any image drift. As a result of the better primary mirror shape, the stars near the edges are smaller and rounder than other images. Half of the sub-frames were taken with one orientation, and after finding a better guide star, the camera was flipped 180° for subsequent exposures.
Previous versions can be found here:
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