FreeLists / az-observing / [AZ-Observing] Re: Mars Is Not "Too Bright"

[Jeff Hopkins <phxjeff@xxxxxxxxxxx>]

>Last night, I uncovered my 20" f/4.3 scope in the backyard for my first
>look through it at Mars.  The 10" f/5.5 is the usual workhorse, and I set
>it up nearby.  Using a newly acquired 3-6mm Nagler zoom at 6mm, the 20"
>provided roughly 350x, which is typically what I've been using for Mars
>in the 10" with a 20mm eyepiece and 5x amplifier.
>
>Unlike other reports from last night, I didn't notice anything special
>about the seeing at my site: it was the usual 2" or so.  What was nice
>was that everybody's favorite hemisphere was presented, with Syrtis Major
>and Hellas approaching the meridian at 10:00.
>
>In comparing the views with both scopes at 350x, the first thing I
>noticed was how much brighter the view in the 20" was (well, duh).  The
>second thing I noticed was how this was nothing but desirable.  Features
>that appeared as only extremely subtle changes in shading in the 10" came
>out as different colorations in the 20".  It was as if I was viewing the
>planet "in black & white" when I went back to the 10".  The last thing I
>wanted to do was suppress the brightness of Mars in the 20".  A dust
>storm that appears to be brewing in Hellas (ask Bill Ferris for a better
>description) was more evident as color differences in the 20".  I could
>only imagine how much better the view through a 40" would be, given good
>seeing and optics.  The lesson I learned (again) last night was that
>aperture wins, and stopping down a scope harms the image.
>
>Finally, another tip of the hat to Mike Spooner, who figured both of
>these mirrors.  The 10" f/5.5 is a fine mirror, but how he achieved that
>figure on the mirror with four times the area and a focal ratio of f/4.3
>is beyond me.
>
>Tom

Interesting as I was also viewing Mars last night with my 8" SCT. 
Perhaps it was my imagination, but I thought Mars looked several 
times better in the 6" refractor. On the west side of Phoenix the 
seeing was indeed close to an 8, best I've seen in a long time.

Jeff



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