Re: ATM Defining Super-Planetary

[Mel Bartels <mbartels@efn.org>]

Here's one prescription for refractor performance (other than buying a
large refractor outright): off-axis mask on large well figured dob.  The
problem with large dobs is that the image swims a lot, and you have to
ignore that for those seconds every once in a while when the image
stabilizes and you get great detail. CCD imaging on big dobs is similar
in that you can select for the best, allowing the large aperture to
really perform for you.  However, many object aesthetically to the
swimming image, so an off-axis mask is the answer.  A 9" off-axis mask
on my old 24" always gave incredible planetary views - better than 8"
refractors.  I feel that in moments of clarity the full aperture did
better, but for that aesthetic view, the off-axis is best.  With the
off-axis, detail inside the Red Spot, resolution of Jupiter's moons, etc
etc is the norm.

If you have a good 6" f/8 you know that it can also do nicely.  But if
you have ever looked through an excellent long focus 8" or even 10" with
small diagonal, the views are most incredible, and frankly I just don't
see the point of extremely expensive refractors of smaller aperture. 
Now that is a bold statement, so I will just say this is only my opinion
based on 25 yrs of observing, and that I certainly acknowledge differing
thoughts.

-- 
Clear skies, Mel Bartels    Programmer/Analyst, amateur astronomer
Eugene, Oregon, USA         homepage: http://www.efn.org/~mbartels
mailto:mbartels@efn.org     atm, atm-digest list-owner
Motorize A Dob: http://zebu.uoregon.edu/~mbartels/altaz/altaz.html