Zero Magnification Sight Tube
Made of durable, high temperature resistant plastic
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It used to be good sextants came with one of these. They were also called clear tubes, and hooded peep sights.Having no lenses, they will not fog or smudge from ocean spray.
They are used primarily for taking horizontal angles where magnification is not normally needed, but where a wider field of view is helpful in identifying objects with respect to one another. They are also used for celestial observations in rough weather, where a wider field of view is helpful in holding the object in sight despite sextant movement. It also makes it easier to initially acquire celestial objects. If for example you normally use a 4 power telescope, the sight tube gives you 3 to 4 times more field of view than you would have with the telescope
We have had many requests for the Sight Tube, and are told that some people simply find sextants easier to use with it than with a telescope of any kind. Although the Sight Tube was designed specifically for the Astra IIIB sextant, it also functions perfectly on most other metal sextants having a standard telescope mounting slot.
The Sight Tube is made of durable, high temperature resistant plastic The interior is dulled to reduce distracting reflections. The exterior is finished in a matte black to match the finish of most sextants. The slip-on rubber eyecup fits on it.
It makes a good accessory at a very low cost.