Spacer Ring to move the primary mirror closer to secondary mirror - Skywatcher Newton 150 mm (6")

Increasing the backfocus by bringing the primary mirror closer to the secondary mirror with a Skywatcher Newton 150 mm (6").

In my case, I could not reach the focus point when using a Baader Clicklock, which is about 18 mm wider than the Skywatcher clamp (30 mm / 12 mm). In addition, the tube of the focuser is intruding into the light path.

Suitable for

This model was done for modifying a Skywatcher Explorer 150/750 PDS. I do not own a Quattro 150/650 but I think the model should suite too. Please leave a comment if you do a main mirror movement on a Quattro 150/650.

Be aware of the size of the secondary mirror when moving the primary mirror (Illumination of the field)

Sizes

Model files with spacer ring thickness of 15 mm and 30 mm for a main mirror movement of 15 mm or 30 mm is available. The FreeCAD model file is available to customize the thickness to your needs.

Part list

• Spacer ring
• Threaded rod M5
• 3 Hexagon Nuts M5 ISO 4032 (DIN 934) (steel or stainless steel)
• Original parts: Springs, knurled nuts, knurled screws, plastic washers (I think they can also be left out).

Printing

Don't be surprised about the small holes, they were added to get walls in the area of the screw which is pressing to the spacer ring.

Weight: 

• 15 mm spacer ring about 70 grams
• 30 mm spacer ring about 125 grams

Nozzle 0.6 mm, layer height 0.3 mm, no brim, no support. 3 wall lines, 4-5 bottom layers, 3 top layers. Infill triangles, density 15% (or more) - it's best to adjust the density so that infill gets bonded on the wall lines of the small holes.

Nozzle 0.4 mm and layer height 0.2 mm is of course possible. Increase wall lines to 5 and 6-7 bottom layers.

Preparation / Assembly

1. Cut the threaded rod to the length you need: 25 mm + mirror movement distance (25+30=55 mm for 30 mm mirror movement).
2. Screw on the nuts, apply screw glue / threadlocker to the end of the thread (not mandatory but recommended).
3. Screw in the threaded rod like it can be seen in the corresponding picture and fasten the lock nut.
4. Insert the spacer ring with the cut out for the nuts onto the nuts.
5. Insert the springs and the metallic end cap.
6. Srew on the knurled nuts onto the M5 threaded rods (and plastic washer), tighten a little bit.
7. Screw in the knurled screws.
8. Mount the assembled mirror onto the telescope tube.

If you need a primary mirror mask / aperture mask like in the pictures, you can find one here:

https://www.printables.com/model/1300503-primary-mirror-mask-d146-mm-and-printed-rubber-mir