Jenkins-Of-Ewelme Web Site


This page will attempt to describe the range of telescopes available at the Ewelme Observatory.  The idea is to impart some basic concepts and experiences in trying to improve an ability to observe and record some of the wonders of the Universe.

This ingeniously simple design has enabled amateur astronomers to own a relatively large reflecting telescope at a lower cost than one attached to a more complex and guided mount. The fact that a large parabolic mirror can be mounted on such a simple mounting, has attracted the nick name of this type as a 'light bucket', since the whole idea of active astronomy is to capture as much light is possible.

Dobsonian telescopes invariably incorporate Newtonian reflecting telescope tubes (OTAs or Optical Tube assemblies).

This one was originally purchased from Ebay at half the price of a new one. It was too heavy and wieldy to carry in and out of the house, so I replaced all the 'formica' covered chipboard frame parts with my own automotive painted, marine ply design, so that it could be left outside all year. The 10" telescope tube was also treated to a change from Hammerite grey to motor vehicle standard waxed white paint. As many plated screws as possible were replaced with stainless steel ones.

To make viewing more comfortable, a rigid plinth was built using layers of standard paving slabs and decking joists. A small stall provides the ability to observe stars overhead (zenith)   

A Dobsonian has an ALT/AZ  mount, meaning that you push/pull it in either the altitude (up/down) or azimuth (side to side)  to observe a celestial object. This is not as easy as it sounds, and a 'finderscope is provided to get the object roughly in the right place, before doing final adjustments while looking through the eyepiece. The rack and pinion focuser provided the ability to fine tune the focus. Eyepieces are changed to suit the object under observation.

The simplicity of the design is shown here, where the altitude 'bearing' consists merely of a plastic wheel which sits on a pair of PTFE (Teflon) pads. A pair of heavy springs ensures the contact is maintained.