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110mm Keplerian refractor telescope

by alex_belov, published

110mm Keplerian refractor telescope by alex_belov Jun 18, 2017
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1029Views 245Downloads Found in Physics & Astronomy


I wanted to create telescope of high light power and low magnification. This set of model is what I created for the project. I printed it with ABS plastic, so some parts models have alternatives that greatly simpify ABS print dealing with warping difficulties. Some parts have alternatives with embedded support to just imprive end result vs. slicer generated support.
All parts use 1mm pitch thread with 60 degree form of teeth.
I got 110 mm x2 magnification lens in my local optics store. Its actual focal length is 270-280mm, while it should be 250mm (4 dioptre).

Unfortunately I did not find lenses with less magnification number (longer focal length) to create telescope of higher image quality.
You can use 1.25''/2'' eyepieces with the scope depending on eyepiece holder you use.

I modeled helicoidal focuser with photo lens similar control. It has 32mm range of focusing, with 10mm position for infinity, so eyepieces with shifted parfocality can be used as well. Since 2'' eyepieces have more deep placement of focal plane the 2'' eyepiece holder accounts this in the model.

The scope is ready to be printed and tested.
Use standard 50/70mm dovetail model with 1/4'' thread (1/20'' pitch) https://www.thingiverse.com/thing:2402072
(thread is standard for photo tripod) for telescope holder tripods. If you already have telescope dovetail you can use it securing it on body brace.
Also blend and lens cover can be added.

Note: do not expect exceptional quality from this telescope since contemporary refractor telescopes have achromatic corrective lens (flint glass) in addition to main crown glass that significantly reduces spherical and chromatic abberations. This scope is limited to 10mm minimum eyepiece use and thus x27-28 usable magnification. Higher magnifications (lower eyepiece focal length) do not give clear view due to spherical and chromatic abberations (polyethylene-like view). So respect $100 telescopes that have flint glass and may give x100 and higher magnification.


  • 06/27/2017 - 0A-eyepiece_holder_2_inch is increased by 0.2mm in internal diameter (after probe print in ABS and test with my old good 2'' eyepiece). New version shall hold 2 inch eyepiece tightly, while previous version did not fit the eyepiece a bit.

Print Settings








Layer 0.1 mm Nozzle 0.4 mm




0.1 mm layer resolution is recommended since most part have thread. Use of sup versions of models is recommended, since it improves result without use of slicer generated support. _sup_04 is for 0.4mm nozze, while _sup_05 is for 0.5mm nozzle.
04-focuser tube has most difficulty with ABS due to warping and uneven cooling of the model. So
sup is must for the model, while model without *sup is just for reference only to have idea how end result shall look.
05-focusing ring has embedded support inside helicoid groove, that shall be carefully removed after print. Spend half an hour to clean it for smooth eyepiece tube movement.
03-body and 06-eyepiece tube shall be printed with slicer generated support to properly print brace and helicoid boss.

Focuser pieces have 0.2mm gap along radius between them, so working surfaces have to be processed with sand-paper after print for more smooth movement.


Clean all parts from brim, sand-paper focuser parts for smooth movement of parts. Use acetone for focuser if it is printed with ABS, and you wish some gloss from ABS.
Assemble parts in the order they numbered. When everything printed well you may glue 03 and 06 parts to prevent their movement during focuser use.

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