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On Sep 22, 2004, at 8:14 PM, Alexandre Eremenko wrote:

> When I said that my Soviet inverting scope is of poor quality
> I did not specify the details (being afraid that my message
> is too long anyway, and may be non-interesting for most
> because of the abundance of detasils). One point about
> this scope is that you
> cannot focus simultaneously on the cross hair and a remote object.
> And this is a constructive defect, not of this particular scope.

 From my experience with microscopes, the reticule is usually, these
days, a glass disk with the cross hairs or parallel lines inscribed on
it.  Frequently, there are two threaded rings that screw up and down
inside the eyepiece barrel to hold the reticule in place, one on either
side.  You use one ring to adjust the focus of the reticule to that of
your eye, then clamp it in place with the other.  It's possible also
that the cross hairs or parallel lines are inscribed directly on one of
the lenses, making focus impossible; I would be surprised were this so.

There may be a microscope maintenance technician connected with one of
the biology or agriculture departments at Purdue who might be willing
to assist you with this.

>> My understanding is that observed lunar distances will be too
>> large if
>> the sextant is not properly oriented.
>
> I don't understand this argument. I don't understand
> how cross hair are going to help. It seems to me
> that the usual "rocking" procedure will do the job.
> But I have not tried the lunar distances yet.
> I tried star distances (as described in Bruce Bauer for
> testing a used sextant).
> The distance Arcturus-Dubhe seems to indicate that my sextant
> error is at most) 0.3'.

Bruce Stark discusses centering the contact of the images in the center
of telescope in his excellent tables, and has a little table in the
preface showing the effect of not being centered.  I believe if one is
looking in one side of the telescope and out the other, rather than
straight down the middle, then the frame of the sextant won't be
parallel to the plane between the objects and your eye.  Bruce recently
acquired an inverting telescope; perhaps he'll jump in here if he's
back from his trip to compare it's virtues to those of the modern prism
monocular.

Oh, by the way, don't worry about burdening me with details in your
postings!  I like them.  I expect most other list members do also.

   

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