NGC 6946 Using the
Astro-Physics 2 inch, 0.67x reducer
This is NGC 6946 imaged 2003-07-28 with my RCOS 12.5 inch RC scope and the new Astro-Physics 2 inch 0.67 reducer for SBIG 2 inch nosepieces.
The rack & pinion focuser of the RC was fixed at a position providing 8.9 inches spacing between the back plate of the scope and the chip in the
ST-10XME. Focus was achieved using the secondary focuser. Guiding was with the internal ST-10XME guide chip.
Other frames taken the night before suggest that this configuration yields a reduction of 0.71x.
Some radial elongation of stars is easily seen in the upper corners, less in the lower corners. Because the elongation is
not equal in all four corners, I'm inclined to ascribe it to non-square mounting of the camera rather than coma.
Details: 6 frames, 10 minutes each, dark-corrected and combined using median combine in MaxIm.
The image was then adjusted with levels and curves in Photoshop.