A 76mm Maksutov-Cassegrain Spotting Scope

This is a 3d printed spotting scope I built from stl files published by "charlesodonnell" here . The original stl files were designed to fit a piece of schedule 40 3.5" pvc pipe. I modified them to fit a slightly larger diameter pipe ordered from amazon. A Blender model for my final design is here . More discussion is here .

03 Sep 2024 Derek Lieber

Lens with aluminized secondary mirror spot:

Lens installed in its mount. Blue 3M painters tape allows a sliding friction fit into the main tube for coarse focusing. No fixing screws are used:

Anti-reflection sleeve installed on lens mount (front view):

Anti-reflection sleeve installed on lens mount (rear view):

Lens mount installed in pvc tube (front view):

Lens mount installed in pvc tube (rear view):

Mirror with central aperture:

Mirror mount (front view):

Mirror mount (rear view). The spring loaded 3mm bolts are for collimation adjustment:

Mirror mount installed in piston (front view):

Mirror mount installed in piston (rear view). The spring loaded 6mm bolt is for fine focusing:

Mirror installed and held in place by threaded baffle:

Piston secured to rear end cap using spring loaded 6mm bolt and white thumb screw (focus adjuster):

Piston and rear end cap slide into rear of tube:

Front end cap slides in to front of tube, pushing lens mount into position to set final lens-mirror spacing:

Assembly is complete:

Sample image using hand held camera (40mm plossl eyepiece yields about 40x power):

Parts list

- lens and mirror set
  - 76MM (3") DIA MAKSUTOV-CASSEGRAIN TELESCOPE LENS SET
  - www.surplusshed.com/pages/item/PL1298.html

- optical tube
    - MECCANIXITY 4.3 Inch PVC Rigid Tube Round Pipe Tubing Hardware Tubing 96.8mm ID 110mm OD 20cm/8" Length White
    - www.amazon.com/MECCANIXITY-Tubing-Hardware-81-4mm-Length/dp/B0D66N14Z4/ref=sr_1_26
    - color  = white
    - id     = 3.8" = 96.8mm
    - od     = 4.3" = 110mm
    - length = 7.8" = 200mm

- 45 degree erecting eyepiece holder
  - SVBONY Diagonal Adapter Zenith Diagonal Mirror Prism 1.25inch 45 Degree Erecting Prism Optical Prism Inside for Astronomical Telescope Eyepiece
  - www.amazon.com/SVBONY-Refractor-Catadioptric-Telescope-Astronomical/dp/B071CKG619

- 40mm eyepiece
  - SVBONY Telescope Eyepiece 40mm 1.25 inches Plossl Telescope Lens Fully Multi Green Coated Metal 40 Degree Apparent Field 4 Element Telescope Accessory for Astronomy Telescope
  - www.amazon.com/SVBONY-Telescope-Eyepiece-Apparent-Astronomy/dp/B01MAZ7LA6/ref=sr_1_3

- 25mm eyepiece
  - SVBONY SV207 Plossl Eyepiece, 1.25 inch Super Plossl 25mm 50 Degree 2 Group 4 Element, Fully Multi Coated for Astronomy Telescope Accessories Astrophotography
  - www.amazon.com/SVBONY-Plossl-Eyepiece-Telescope-Astronomy/dp/B09JNT6QRZ

- compression spring assortment
  - www.amazon.com/Compression-Assortment-Stainless-Different-Individual/dp/B09VZH6NS1

- miscellaneous M3, M4, M6 bolts, nuts, and washers

- 1/4-20 tee nut (for attaching scope ring base to standard camera tripod screw)

- flat black spray paint