Nebulae in Orion
The right 85% of this image is an average of 6 images, taken shortly before transit. The focus in the first acquired image was very good, but the lens was still cooling and succeeding images became slightly defocussed, with blue haloes around stars. A second series, taken after transit, was in better focus but reversed - with red haloes. The second series was used to expand the field of view, adding 15% to the left-hand edge. During processing, the brightness of the nebulae was enhanced and the overexposed core of M42 was taken from the unenhanced version. There was slight elongation of stars in the vertical direction in some frames (and severe in one), almost certainly because the blocks my mount was on settled into the snow: RA tracking was excellent. Winter skies can be beautifully clear, but it's hard to find good ground.
The images were acquired on the weekend of a terrific snowstorm in the eastern US, and moderate winds were predicted at my location. But they did not materialize and the crystal-clear skies were very calm.