Re: ATM Focal ratio/length question

["Bill T." <twentiethwave@hotmail.com>]

>From an ergonomic point of view,  I suggest you measure the comfortable
standing eye height of the main observer, subtract 2 or 3 inches, and divide
that by your mirror diameter.  That's your "backbone-friendly" f-ratio.
This will typically give you an eyepiece height such that you can stand
comfortably while observing at high tube elevations, where viewing is the
best.  This way you don't have to grovel around on the ground so much, a
common and fatiguing problem.  For an 8", f8 is about right for most adults.
The kids will have to climb a small ladder, a big help in burning off excess
energy.  The long focal length is very desirable for planets.   FWIW.

Bill T.