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On Wed, 22 Sep 2004, Fred Hebard wrote:

> From my experience with microscopes, the reticule is usually,
> a glass disk with the cross hairs or parallel lines inscribed on
> it.  Frequently, there are two threaded rings

No, this one is much less sophisticated.
The cross hairs are just ordinary real wires rigidly attached
to the tube. The whole scope has only one adjustment parameter:
you can make the tube shorter or longer. That's it.

More precisely, the scope consists of two tubes which fit
tightly one inside another. The thiner tube has the objective lens
rigidly attached in front, and the crossbar hair (wires)
attached to the other (back) end. The thicker tube has the eyepiece
rigidly attached to its back end and the front end is open.
The back of the objective tube is inserted in the front end
of the eyepiece tube. That's all.
To focus you hold this assembly with two hands and move
one tube with respect to another.

So this is the most primitive "Kepler telescope" you can imagine.
(As a child, I made such telescope myself, but never used it
because it was inferior to my binocular, despite the higher
magnification power and larger lens diameter).

The stars look surrounded by round spots of light, like hairs
of light sticking from the star;
these spots are excentric unless the star and your eye are
exactly on the optical axis, in which case they are perfectly
round with the star in the center.
(I thought this is called "spherical
aberration, is not it?)


> Bruce Stark discusses centering the contact

His book is on my shopping list, right after the Almanach:-)

Alex.

   

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