On Sat, 18 Sep 2004 15:13:42 GMT, "D. Couillard"
wrote:

I know that there are practical upper limits for magnification for a given
scope, but is there also a practical lower limit to magnification? I built a
10" F5 truss tube dob and used a 1.25" focuser on it. My lowest power
eyepiece currently is a 32mm Plossl (40X). So, how low can I go, and would
there be advantages other than FOV to lower power with my setup?
BTW my highest power eyepiece is a 13mm Nagler (97X) and I carry a 2X
Barlow.

The lower limit in a newtonian or other telescope with a central
obstruction is when the size of the shadow of the secondary mirror
begins to approach the size of the entrance pupil of your eye. When
that happens you get an obvious and annoying black spot in your field
of view.