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Dear George,

Thank you very much for your most interesting message.
(Someone already complained on the list that your
messages are hard to read because they do not contain
line breaks. With my mail program I read then easily,
but to REPLY a long message from you is a real
pain, exactly for the same reason: there are no line breaks,
your paragraphs consist of single line of text each).

Back to your message:

Your explanation of the index mirror bending
is very clear. I checked my sextant: it has ONE
adjusting skrew and three springs. One of the springs
is opposite to the adjusting screw. The whole configuration
looks like this:      :+
where the dots and the plus sign mean the springs, and the
adjusting screw is behind the + sign.
I assume that the sextant is hold with its frame plane vertical.

So the design seems sound to me.

> The complaint that Alex makes, about a doubled star image,
> with a weaker displaced image or tail as seen in the mirrors,

I would not call it "double". I would rather say it is
somewhat "blurred", and of irregular shape. It LOOKS
like an image in a low quality scope.
But the OTHER image, through the horizon glass looks
like an image in a good quality scope.

I can certainly test the spare mirror that I have.
And your idea of putting a diaphragm on the mirror,
decreasing its effective size is great.
If the reason is the mirror deformation, then the diaphragm
should evidently decrease it.

It is probably also possible to design an experiment that
will show which mirror is really responsible
for my problem: I am just
thinking of fixing the sextant somehow and looking
into the index mirror through the detached telescope
(which I can hold in my hand) under different angles.

(My main technical problem with all such experiments
is the shaking of the wooden balcony floor as I move; this
also almost prevents me from using the art horizon.
But I will invent something to overcome this:-)

BTW, do you think it safe for the eye to use a laser pointer
in the experiments? Together with Sun filters, of course:-)

It looks much less bright than the Sun.

Alex.

   

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