I wanted to get an idea of how big a patch of sky the Dwarf 3 can image when using the telephoto lens. Here is the unprocessed image of M31 I took on December 21st last year:-
It is a shame, in some ways, that this full frame is cropped so much by the post processing. This frame is 3856x2180 pixels. To get an idea of how big an area of the sky this is we can use the positions of the two attendant dwarf elliptical galaxies M32 (lower centre) and M110 (upper centre). M32 is at RA 00h 42m 41.8s and Dec. +40 51' 55''. M110 is at RA 00h 40m 22.1s and Dec. +41 41' 07''. Using my program to calculate the separation of these two objects I find that they are 0.929 degrees apart. Using Photoshop to view this image I find that M32 and M110 are 1204 pixels apart (based on an average 4 measurements of the separation). So this implies that 1 pixel is 0.929x60x60/1204 = 2.78 arc seconds. This is the plate scale. This agrees well with another observer's calculation of 2.75 arc seconds per pixel.
This means that the full frame is something like 2.98 x 1.68 degrees. This is somewhat larger than the field of view of my Celestron NexStar 102 SLT with my D90 camera at prime focus (this has a field of view of 2.07x1.38 degrees) but not excessively so.
All text and images © Duncan Hale-Sutton 2026
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