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Ken Gebhart wrote:
>
> We also have another type of collimator which is simply a tube which emits a
> collimated reticle.  I haven't taken the time to figure out exactly how that
> is supposed to work.

I have seen collimators of that type at a survey equipment shop. Three
were attached to a heavy vertical I-beam to provide artificial targets
at approximately +45, 0, and -45 elevation. Their optical axes
intersected just above a pillar a few feet away, on which the theodolite
under test was mounted.

Maybe a marine sextant could be tested with that setup. You'd have to
hunt around for the sweet spot where the collimator beams hit the index
mirror and horizon glass simultaneously.

With a precision rotary indexing table and two collimators, a marine
sextant can be tested at any desired angle. I once saw the mil spec for
the Navy Mark III. That's the method it used for checking the sextant.

A single fixed collimator would be enough to test a bubble sextant at
one angle. The angle could be checked with a theodolite shot
after mounting the collimator.

   

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