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The Kutter Schiefspiegler

A simple tilted component telescope for the amateur

[Schief, Side View] [Schief from Front]
A Simple Schiefspiegler, drawings by Oscar Knab

The Schiefspiegler is a tilted component telescope invented by Anton Kutter. One may think of it as an off axis segment of a Cassegrain, but rather than having the fast primary (typically f/2 to f/4) and high secondary magnification (typically 3 to 4 times) of the normal Cassegrain, the Schiefspiegler has a long focal ratio for the primary (typically around f/15) and a smaller secondary magnification (typically 1.6x).

Schiefspieglers are very long focus instruments. The instrument listed above is a 4.25 f/27 instrument. In the times of 20" f/4 instruments, one might wonder why this instrument would be desireable. A number of reasons leap to mind:

So, what do you need to know to build a Schiefspiegler of your very own? A quick trip to your local library should net some articles that have been published in Sky & Telescope. Articles appeared in the Gleanings for the ATM by Oscar Knab and Anton Kutter, describing the basic Schiefspiegler and the tri-schiefspiegler that came later. Oscar Knab also had a short article on building a 3" f/20 Schiefspiegler in Telescope Making #3. I strongly recommend that you read these articles, they are very useful. Above I have reproduced the diagram for the 4.25" Schiefspiegler. If you click on the image above, you will get a version of the diagram digitized at 300dpi. It contains most of the critical dimensions, and will be quite useful in understanding the basic mechanical layout. Below is the design for the smaller three inch f/20 instrument, also by Oscar Knab.

[Smaller Schief]
A Smaller Schiefspiegler, drawing by Oscar Knab

Designs for Two Small Schiefspieglers
Measurements for 4.25" Kutter Schiefspiegler
Primary mirror aperature4.25"
Secondary mirror aperature2.20"
Radius of curvature127.5"
Effective focal length111.0"
Mirror separation36.0"
Secondary/focus separation46.45"
Primary tilt2.76 degrees
Secondary tilt6.41 degrees
Measurements for 3" Kutter Schiefspiegler
Primary mirror aperature3.00"
Secondary mirror aperature1.44"
Radius of curvature81.5"
Effective focal length71.0"
Mirror separation23.13"
Secondary/focus separation29.00"
Primary tilt2.9 degrees
Secondary tilt6.78 degrees

This page Copyright 2001, Mark T. VandeWettering. Permission is granted to reproduce and distribute these files for non-profit, personal use.

Mark T. VandeWettering

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