Better images will be obtained however if the telescope is allowed to cool for about half an hour before serious observing is attempted. To enable a beginner to see astronomically interesting objects other than The Moon and the larger planets, a telescope of at least 150mm is required and most Dobsonians are of at least this size.Ī 150mm Dobsonian is very quick to set up, in most cases all that is needed is to carry it from its place of storage to the observing position. It is also a large powerful telescope made available at a modest cost. Using a Dobsonian is very simple design making it an ideal telescope for the beginner. Once centred the object should be visible in the main scope. The finder has a wider field of view so can be used to find the object first. This makes it very difficult to locate a specific object. An astronomical telescope has a very narrow field of view, this means that only a very small area of sky can be seen. To help the observer to find and object a smaller telescope is fitted to the tube of main telescope this is called a Finder. Drives are not normally fitted to this type of telescope. The telescope can therefore be aimed at any point in the sky.
#DOBSONIAN TELESCOPE FULL#
These panels are mounted on to a turntable that allows the telescope to be rotated through a full circle. The cups are fitted to the tops of two supporting ‘Cheek' panels. This allows the tube to be aimed up and down. It has a Nylon disc mount on either side of the tube that sit in Nylon cups to provide a trunnion type bearing. The Skyliner shown above is a typical 150mm (6 inch) shop bought Dobsonian telescope retailing at about £230. Using a variety of eyepieces with different focal lengths, higher or lower magnifications can be obtained. The eyepiece is a simple microscope used to magnify the image formed by the mirror. A focusing unit is fitted to the hole to hold and adjust the eyepiece. To enable the observer to study the image without blocking the light entering the tube, a second ‘flat' mirror, is mounted at the top of the tube to direct the light out through a hole in the tube. Because the mirror is curved the light focused into a point where an image is formed. Light from a distant object enters the open tube and is reflected back up the tube by a parabolic (concave) mirror. Shown below is the layout of the optics of a Newtonian tube assembly. It is generally based on a Newtonian reflecting telescope tube supported on a very simple mounting. HINTS ON OBSERVING This article featured in the February 2004 Beginners Magazine USING A DOBSONIAN TELESCOPEĪ Dobsonian is a type of telescope designed by an American named John Dobson.
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