Re: [ATM] Ideal Magnification for Public Terrestrial Telescope?

["Stars" <rocketmaker@intergate.com>]

Hi Art, David:

I sent this to David yesterday but since you touched on some of the 
sub-topics I will post it.

Hi David:

There are a few considerations that you haven't mentioned but let me
suggest.

I would surmise that since this is for the public that perhaps you do not
want to be changing the eyepiece. A Zoom eyepiece or a turret as suggested
probably would be the way to go. They could even be fixed with set screws.
Be a shame to lose one or have it dropped. What is the ideal power, is 
always
a question even for celestial viewing. Here are some considerations. Size
and focal length of the scope maybe should be selected based on the
eyepieces instead of the other way around.

Let's say the ideal is a 3x zoom. I believe most eyepieces will fall into
this 3x range. Let's jump to power. 10x Binocs are common so lets say you
want 20-60 power. For public viewing both day and night I have 20x100s These
work so well but sometimes I would like just a little more magnification.
They also work so much better than 25x100s at night.

For daytime use then I am going to suggest a 100mm APO. I don't want to seem
elitist but almost any daytime object is going to exhibit residual color
like a nightime bright star. Now I also recommend 1.5mm  minimum exit pupil
for comfort of viewing.This helps minimize distractions from floaters and
other defects in the eye that can be exacerbated by turbity. That would
place a top limit of 67 power for magnification so 20 to 60 power for a
100mm objective should be ideal. A zoom eyepiece of 8mm-24mm would then need
480mm of focal length. If the eyepiece has a 60° AFOV then the focal lenght
could be 760mm followed by a 44mm (or even 38mm) diameter f:6.3 focal
reducer. I have not built such a system but if I were to, this is how I
would do it. Business may require I be traveling between China Lake and San
Diego on a weekly basis, I would love to stop by and have a peek if you
build it.

BTW my favorite power is 20x using a 3" dia. 96° AFOV (more or less anyway)
eyepiece. There is few things as beautiful than Andomeda Galaxy rising
behind  tree branches a few miles away. The the same eyepiece at 28x with a
2" HaHbO3aO3b filter shows the whole loop glowing like Foxfire. I have three 
of these but may make some more as I get my lab back together.

Clear Skies.
Rick 

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