Triple APOD - April 22, 2025: M81 & M82 By Wayne Malkin – All-Star Telescope Canada

Triple APOD - April 22, 2025: M81 & M82 By Wayne Malkin

From Wayne:

Here are a couple of images from the last month or so. The first includes M81, M82, and other things in the neighbourhood. The second is a more detailed view of M81 alone. These were shot with very different imaging trains and represent really different approaches to imaging. I am including a few notes for each. Both were shot with an Astro-Physics Mach2GTO mount unguided, which has absolute encoders and is a pretty high end mount, but I imagine similar results could be obtained with any decent mount and a well tuned guiding setup.

The wide field version is an ASI2400MC on a Takahashi FSQ-106N scope (2000 vintage) at 530mm focal length. The large pixels on the ASI2400 yield 2.3 arcsec/pixel, which is a little under sampled for Edmonton skies. The ASI2400 is full frame (24x36mm) giving a 2.3 degree field of view at 530mm. The full frame sensor also requires a large flat field from the scope — the FSQ-106N is a perfect match in this respect. This scope also has the rear corrector elements mounted in front of the focus tube, so back focus is automatic. If you come to focus, you automatically have a large flat field. The image includes almost three hours of data at one minute subs.

The second version is an ASI585MC on a Takahashi MT-160 Newtonian (1988 vintage) at its native 1000mm focal length. The ASI585 has small 2.9 micron pixels, which at 1000mm focal length yields 0.6 arcsec/pixel. This is quite a bit over-sampled for our skies. This small sensor (1/1.2”) sees a 0.35 degree field of view, less than 1/6th of the wide field version. It also sees only the centre of the field, so it works well with a less corrected field.In this case, the absence of a flattener or reducer in the imaging train means backfocus is not an issue. The image includes only one hour of data at 30s subs and f/6.2. Considering the focal ratio and integration time differences, the wide field version has about 4.5x as much raw data.