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Re: (meteorobs) Definition of "seeing"
On 23 Apr 2001, at 22:27, Robert Gardner wrote:
> What brings this to my mind is that the improved LM in my
> back yard last night I think was due to the good "Seeing".
Yes, I think that is a key issue. The smaller the spot into which
you focus a stars light will increase its apparent brightness. You
can easily demonstrate this by looking at a faint star and defocus
your telescope slightly, and it will disappear. Be it poor focus,
aberrations in the instrument or your eye, or atmospheric seeing,
they all smear out the image from the ideal perfect diffraction
pattern and reduce LM.
I believe this explains much of my own observations, since I can
see fainter LM in a high quality optical instrument comparedto my
naked eye. I have uncorrected astigmatism, which prevents perfect
focus by naked eye. However, when looking through a telescope, I
can adjust the focus to compensate for astigmatism to a degree,
which allows for fainter LM. Typically if my NELM=6.3 my LM=14.9
in a 25cm aperture.
Clear, high acuity observing!
Mike Linnolt
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