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One late comment on visibility of faint objects with and without optical
aids: I have a very clear southern horizon which allows me some nice
summer views of the Scorpius - Sagittarius nebulae. I use a well-mounted
11x80 binoculars on clear nights. However, when there is a background
haze to the sky, the large binoculars do little to bring out the Messier
objects. Yet if I switch to my modest pocket Nikon 9x25s, there they
are! My uneducated suggestion is that it would seem that there is a
visual thresh-hold beneath which the eye sees complete black. With the
pocket binoculars the hazy sky was below that level, and the nebulae
above it, and they were visible, despite the small amount of contrast
between the two. The large light-gathering 11x80s elevated the
background sky above that visual level, and the sky and nebulae blended
into each other.
So on good nights I use the big binoculars, on bad nights the little
ones.
William F. Robinson
rarebook_at_iconn.net
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