FreeLists / az-observing / [AZ-Observing] Re: The Orion 120mm ED Refractor

[Brian Skiff <bas@xxxxxxxxxx>]

     As Jack, Dwight, and others have intimated, depending on the
intended use, the type of glass and supposed color-correction may
be only a minor consideration.  If you intend to do imaging of some
sort, then the mechanical aspects will be of higher importance---
a rigid mount and couplings capable of dealing with the extra hardware
without flexure.  If there is flexure in the system, slightly soft
images are going to be the least of your problems.  For casual
observing with eyepieces only, probably a large number of the
near-identical offerings at the cheap end from various sources will be
adequate.  Once you start thinking solar observing, or planetary, etc.,
then you'll have to think about better correction, longer f/ratio,
solid mount and the mechanical stuff at the business end of the
tube assembly, all of whioch mean more $$$ unless you make the
parts yourself.

     What is Charles Juels using for his near-Sun comet search from
Fountain Hills?  The first comet, C/2002 Y1, was done with what the
relevant IAU Circular describes as "0.12-m f/5.0 refractor".
Was this a 5-inch Meade with a focal-reducer?  The second comet
(C/2005 N1) seems to have been done with a telephoto lens, since
the instrument is described as a "0.07-m f/2.8 refractor", which
sounds to me like a 200mm (focal length) f/2.8 telephoto.  Evidently
the aim was to increase sky-coverage at the expense of going fainter.
If he's running the fast telephoto wide-open and unfiltered, then
the images will suck, but obviously succcessful for the intended purpose!

\Brian
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