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On 2014-10-24 21:41, Francis Upchurch wrote:
> Does anyone know of modern equivalents for amateur astronomers to measure 
small angular differences (eg double stars) via a telescope?

Filiar micrometers are still manufactured, but a good new one like the
NEEDLEYE is about $2500. It's a beautiful device, though.

http://www.observatory.org/bfm.htm

At the other end of the complexity spectrum is the ring micrometer,
which has no moving parts. In the old days it was a precisely circular
metal ring cemented to a slip of glass at the focal plane or perhaps in
a special eyepiece. I don't think any such thing is available anymore,
so nowadays the edge of the field of view is the "ring".

With a ring micrometer Earth rotation moves the objects through the
field. The appearance and disappearance of both bodies is timed with a
stopwatch. Chauvenet vol. 2 chapter X explains the principle and the
formulas for reducing the observations:

http://books.google.com/books?id=eTs5AQAAMAAJ&pg=PA3

For a much more recent book, see "Observing and Measuring Visual Double
Stars," edited by Argyle:

http://link.springer.com/chapter/10.1007/978-1-4614-3945-5_12

Here a beginner at double star measurement reports results with the ring
micrometer method:

http://www.cloudynights.com/page/articles/cat/articles/how-to/learning-to-measure-double-stars-r1173

   

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