Four inch scope, close-in resolution

From: RichA (none_at_none.com)
Date: 12/15/04 

Date: Wed, 15 Dec 2004 13:25:25 -0500

A four inch telescope should resolve an object
on the Moon about 1.12 arc secs in size. That's
roughly 1 mile across. No detail can be seen in
the object (for e.g., a crater) but you should be able to
see the object. So the resolution ratio is around
236,000:1 (distance of the Moon in miles versus the smallest
detail seen on it). Saturn's Cassini division can also
been resolved easily (owing to contrast) and it's about
2200 miles across but it's over 800 million miles away,
so it's only 0.7 arc seconds across or even less, given
the tilt we see Saturn's ring system at.
But, have any amateurs tried to duplicate this kind of
resolution on a nearby land-based object?
With a 4" scope, you should be able to see a bird at
a distance of 44 miles! It would appear as a black
spec against the sky, but that resolution is the same
as we get when we look at the Moon.
Another couple examples might be car at a distance of
600 miles, but resolution would be reduced owing to
contrast being less than a side-lit object on the Moon
or a bird against the sky. Another example would be
the mesh on a window screen (good contrast) at a distance
of 1600 feet. Or for extremes, use a long extension tube,
stop the scope down to 2" to get rid of spherical aberration
and look at cells in a leaf on a tree at a distance of
38 feet.
Has anyone ever tried achieve resolution terrestrially
that comes close to what we achieve celestially?
-Rich
Has anyone come close to this kind of resolution on land?
-Rich

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