Re: [ATM] Odd question...

["Bob May" <rmay@nethere.com>]

This is interesting for a discussion.
I'll note that when I went and found the focus point of my optics
for my 200" refractor, I used the sun one morning out at Blair
Valley which is in the desert east of San Diego as the light
source.  The guys that saw me do this were all sure that I had
lost my mind that morning!  Truth of the matter is that the sun's
image was so large, about two inches in diameter that the 4.25"
lens hardly magnified the image over the natural amount of heat
generated by the sun and my hand hardly felt the warmth of the
sun on that cold morning - there was still frost on the ground
when I did this.
What I'm pointing to is that it isn't the diameter of the opt9ics
that is so improtant but rather the concentration of the light at
the focus of the optics.    The little 60mm department store
telescopes with their F15 or so focal ratio concentrate the light
little enough that a eyepiece filter is safe enough that it can
be used for a while without destroying the telescope. Do the same
with a lens of a much shorter focal lenth and the fire wil start
as the concentration of the light will be a lot larger.   This is
kind of like why galaxies have such highbrightness levels
associated with them and yet they are so hard to see as the light
is what it would be if the light was coming from a point source
rather than an area source.
Bob May

rmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net


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