Celestaire's 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.
Sight tubes 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