Friday, January 13, 2017

Astroscan focuser mod

After seeing the eyepieces for the Astroscan discussion on the CN forum I decided to showcase my simplistic focuser modification, which I use to convert my Astroscan into a powerful 101 deg AFOV monocular which I'm often enjoying between 12" dob sessions.


It's basically an adaptor between Astroscan focuser's drawtube opening and the WO UWA 9mm eyepiece with 101 deg AFOV.
The drawtube hole is going through a fairly thin plastic wall (about 3mm), so in addition to the short barrel going inside for about 8mm, the paracord string was used to keep the adapter tight against the front side, which is perfectly orthogonal to the optical axis. It works very well keeping everything reliably attached. The WO eyepiece fits into the adapter extremely snugly. The length of the adapter is very close to the perfect focus but it is possible to fine tune it moving the EP in and out to compensate for about 1 diopter difference between my left and right eyes. In case my eyesight gets worse, I'll just re-print it longer or shorter as necessary.


The paracord's diameter is ideal to fit snugly under the focuser knobs on both sides. The holes diameter in the adapter is such that two cords can fit with good friction, which allows tightening everything gradually by hands and then tie the final knot easily without a chance loosing the tension.


The ultra-wide view is really spectacular at 50x and it is very comfortable as you don't worry about heavy EP falling in or out which is the case with the original focuser. The OTA balance is not that bad either if you keep the EP on top of the OTA (as pictured on the first image).

Construction

Printed it out of PLA with 0.2mm layer height after three test prints to adjust two crucial for the tight fit diameters, one length important for the perfect focus, and the third one because I decided to add lashing holes to it to ensure it couldn't fall apart no matter what.

Full screen interactive 3D Preview.



ToDo:


  1. Blackening the inside.
  2. Try the 2" adapter for Ethos 17.

No comments:

Post a Comment