Reed's Sextant Simplified

On the forty-second page of “Reed's Sextant Simplified” author Dag Pike wrote (emphasis added):

Chapter Seven

Sextant Telescopes & Other Accessories

In the past good quality sextants would come supplied with a number of telescopes, each one designed to allow the best observations to be made in the easiest manner under specific conditions. The more expensive the instrument, the more superior would be the telescopes provided in order to allow observations in marginal conditions. Now with improved telescope technology most modern sextants come with just one telescope. Alternative telescopes are available with many modern sextants as an option but these are generally only required for specific observation tasks. Here we will look at both the old and the modern approach to sextant telescopes so that all types of sextant currently in use are covered.

No attempt will be made to go into the theory of the construction of the different kinds of telescopes, but we will look more at the various practical points that arise for the navigator who wants to get the best out of his sextant and to be able to optimise the viewing of both heavenly bodies and shore objects.

In any telescope the end farthest from the observer, which is generally the larger end, is called the object glass, and the end towards the observer, the smaller end is called the eye piece. With the older type of sextant telescope the lenses in this eye piece are fixed in a separate tube which is generally called the "draw" of the telescope which slides in an outer tube. This movement of the eye piece in or out allows the telescope to be focused for different eyes. On modern telescopes this focusing arrangement is generally by means of a screw adjustment on the eye piece similar to that found on binoculars. The screw adjustment allows for finer focusing and is also less likely to be unwittingly adjusted by eye pressure. With the draw tube system, when the telescope has been focused and the objects have been made to appear well defined and distinct to an individual observer, it is often the practice to make a

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