April 2022
I recently decided to upgrade my Orion ED80T CF Apochromatic Refractor into a true Astrograph. My internet researches suggested that the ED80T CF was a triplet capable of making really nice images (e.g. found good examples on Astrobin) , however, the stock focuser could not handle my SBIG camera without sagging under the weight of it. And, as most refractors, it needed a field flattener to get sharp stars across the image plane.

My intention was to ensure that the newly acquired focuser and flattener could be use with the 80EDT CF or any other premium refractor I might want to acquire in the future.

I then contacted Ron at Moonlite and ordered a focuser upgrade and online ordered a 2.5″ field flattener with the required extension rings to ensure correct back-focus.

The field flattener I opted for is the Sharpstar Optics 2.5″ Field Flattener – FF25L which I ordered from Telescopes Canada. The unit I received is different from the on that can be seen on all the websites you can buy it from. The two differences are:

1. The extension tube is not tapered but cylindrical
2. The extension tube’s length is 33mm instead of the advertised 36.5mm

Major Modification to the OTA

I had to cut to OTA of my ED80T CF by 28mm in order to be able to reach focus with this focuser/flattener combination. I also had to fabricate a sanding jig to square off the OTA after cutting it using a diamond blade on my 12″ miter-saw. Nerve wracking operation!

Design & Print of 90mm Rings

90mm-Rings-with-Apo

Assembly

  • Orion ED80T CF
  • Moonlite CFL 2.5″ + Threaded (68mm) 4.5″ Drawtube + High Resolution Stepper Motor
  • Sharpstar 2.5″ Field Flattener
  • M48-M42-28.4mm + M42-M42-6.5mm Extension Rings
  • 3D Printed 90mm Rings
  • D-Style Dovetail
  • Vixen Dovetail
  • SBIG ST-8300M Monochrome CCD
  • FW5-8300 Filter wheel
  • LRGB and HOS unmounted Baader filters (3mm thick)
  • APM 60mm Image Master Guidescope
  • QHYCCD 1.2 megapixels monochrome QHY5L-II-M

Weight of Equipment

7.175kg or 15.82lbs

Back-Focus Calculation

Focus Calculation

Focuser Step Size: 0.00016″ or 4.064 microns (at full step)

Drawtube lenght: 4.5″

Maximum number of Steps: 4.5/0.00016 = 28,125

Field of View and Image Scale