[AZ-Observing] Re: Seeing Scale Simulation
- From: "Thad Robosson" <starstarcracker@xxxxxxxxx>
- To: az-observing@xxxxxxxxxxxxx
- Date: Tue, 8 Oct 2002 07:50:49 -0700
> After thinking about this some more, the multiple rings I saw must be
> the result of the central obstruction throwing more light to the rings
> (taking away from the disc) that makes more than one visible in a
> Dall-Kirkham. It probably is not an optical abberation, but a
> characteristic of the optical system.
If I may add a point to this discussion, allow me to quote Webb Society
member Tom Teague on this very topic....(from another mailing list.)
"This is actually one of two scales devised by Pickering. Two points are
worth noting:-
1) It is not intended for use with other apertures, but was specifically
designed for a 5" objective.
2) Pickering intended that assessment of the seeing according to this
scale should be carried out with a magnification of not less than x25 per
inch on a test star of magnitude 1 or 2.
Even a fairly small difference in aperture from the 5" norm makes this scale
unsuitable. Thus, Pickering's other scale (of which the scale presently
under discussion is a development) was designed for use with a 6" aperture,
employing a magnification of between x150 and x240 (i.e. 25 - 40 per inch).
The 6-inch scale had 6 points, rather than 10, and was consequently simpler,
but all the numbers were even, so it's clear that Pickering envisaged
intermediate levels up to a maximum of 12 points.
There is an interesting discussion of these and other seeing scales in
Sidgwick's AAH.
Tom"
Hope this clears some of the confusion...
Thad
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