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I've been comparing a few "straight" lower-magnification (approx. 3X to 4X)
and higher-magnification (6X to 8X) prism sextant scopes .

I have a few questions:

1. How many lens elements should I expect to find in 3X to 4X power
"straight" scopes?

2. How many lens elements should I expect to find in 6X-8X prism scopes.

3. How many lens elements should I expect to find in a 6X inverting scope?
(I know Alex has the answer to this, as he has disassembled his SNO-T
inverting scope).

4. Does the f-ratio (focal length over objective lens diameter) hold up for
prism optics?

Now the sticky wicket--determining magnification. Problem at hand, no lab,
no optical bench, no degree in optical engineering.  I need to take sextant
scopes with no specs (except diameter of objective lens, and determine their
respective magnifications.

All I can figure is to focus all the scopes with a given eye, solidly tripod
mount them, put shades (filters) in front of the objective lens to protect
the (glue?) mounting of lenses/prisms from the heat (noting an astronomy
caution that telescopes can take the heat, but binoculars cannot), and point
at a known object (sun?).

Then introduce a target (piece of white board) behind the exit pupil and
move them to bring the sun's projected image into sharp focus (like viewing
the sun through a telescope and projecting it onto a piece of paper/board).
Measure and compare the diameter of the projected circles to the sun's SD.
(Caveat here being that image size will change as the scopes focus--barrel
extension--is changed. Hence common focus. Much easier if the magnification
of one of the scopes is known as a reference.)

Any thoughts would be appreciated.

Thanks

Bill

   

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