Cherokee wrote:

Ed,

How did you get the magnification numbers? I'd like to calculate those
for my Pronto.

Ed, Brian,

What eyepiece should I buy to be able to split these 2? If I need
higher magnifications for certain objects, I best buy it right away so
I don't have to skip viewing them.


The usual rule of thumb says you can make use of 2X per millimetre of
aperture under excellent conditions. So for the maximum useful
magnification you want an EP that can deliver something like 120X -
150X -- depending on how optimistic you are. Dividing that into the
focal length of your objective, which Ed said is 480 mm, gives a
range of 3.2 mm (somewhat optimistic) - 4 mm (more conservative), but
considering that you already have a 2X Barlow you can combine that
with an EP of twice the FL for the same result. For example a 7.5-mm
eyepiece will give you 480/7.5 = 64X alone, or 128X with the Barlow.

--
Odysseus