That brings up a related question. If you can make out the central
obstruction in the daytime with, say a 7mm exit pupil, It's still there at
night decreasing contrast right? It's just harder to see. What exit pupil
shouldn't you go above with a 33% CO if one doesn't want contrast decreased
on axis?

--

Thanks,

Chuck

"Frank Bov" wrote in message
...
As Bill noted, the low power limit occurs when the secondary obstruction
becomes evident. However, he didn't say when that occurs. In my
experience,
I find a 10mm exit pupil still acceptable with a 22% obstruction as long
as
I'm well dark adapted. YMMV.

Part 2 relates to the advantage of low power - a wide field of view. The
only variable here is the field stop diameter of the eyepiece. Once you
hit
27mm in a 1.25" focuser, you're maxed out. A shorter focal length will
give
a more appealing view, thus the 24mm Pan, but your 32mm is just fine. A
40mm
would give a less appealing image than you have now.

However, with a 2" focuser, you can get a 46mm field stop and the total
field of view nearly triples. The highest power at this field stop is
typically about a 40mm eyepiece. You will lose a little brightness, unless
you eye can open to 8mm, but you're not likely to see the secondary
obstruction unless your secondary is unusually large.

Have fun,
Frank

"D. Couillard" wrote in message
news:GgY2d.22947$yW6.9263@clgrps12...
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.
Thanks in advance.
Duff Couillard