* Back in the saddle! A series of mono images from 2022 *

I got some of the extended outer halo of the galaxy, which is nice, but most important was the resolution of the dust lanes in the center. This image is a mayor step-up in sharpness compared to my 2019 version, shot with the TS 80mm APO. Notice how the stars and galaxy details almost snap into better focus in the animation below.



Technical
I decided to face my nemesis: sensor tilt. The reason I have been so reluctant to tackle this, is that the working distance of my GPU coma corrector (53-55 mm, depends on telescope focal length) is too short for all my accessories. That meant I could have either OAG+EFW, Tilter+EFW, or OAG+Tilter, but not all 3 at once. I decided to ditch the filter wheel, and to troubleshoot everything with a single filter in the OAG+Tilter setup.



A 1.25″ luminance filter was screwed directly on top of the sensor window with the aid of a special adapter (ZWO shipped this with the camera). This allowed me to take proper images without a filter wheel, but also meant I was not going to shoot color pictures.



In the end I did not get the image perfectly flat, but the center looked acceptable. The body of the tilt unit was measured using precision calipers and the actual thickness was 11.2 / 11.4 / 11.7 mm on a diameter of 78mm. My sensor diagonal is 22 mm, indicating there was up to 0.14 mm tilt across the sensor plane. That’s very significant, given that the critical focus depth at f/4 is only 0.04 mm (40 microns).

The scope was performing much better after reducing the tilt, and luck was apparently on my side as we then got 5 consecutive nights of clear skies in Belgium. I decided to spend this time on several galaxies in the Northern part of the sky, where we have the best seeing. The images in this run had a FWHM between 2.1 – 2.3″, where objects in the lower Southern sky (like my recent HCG44 or M100 ) had resolution between 3 – 3.5″ FWHM. That’s a huge difference in sharpness. PhD2 was setup with multi-star guiding on 4 second exposures and the mount was tracking with PPEC.

Color data for revision D comes from my older image shot with the TS 80 mm Triplet Apo:


M63 HaLRGB - A tiny Sunflower