Clarky wrote:
I was just looking at the dobsonians again, and had another question.
Both the Celestron 10 inch and the Orion 10 inch both say that they
have a "maximum useful magnification" of 600. The Hardin 10 inch
Dob's "maximum useful magnification" is only 250. I know that
magnification isn't all that important, but that seems like a pretty
big jump, although I'm not sure 'cause I'm new to all this. Does
anyone have any thoughts on why the Hardin would be so much lower than
the other two?

Conflict between two rules of thumb. It is pretty unlikely that the
discrepancy indicates any real difference between the optics.

One rule of thumb says that the maximum useful magnification for a
scope of aperture N inches is equal to 50 or 60 times N (depending on
whom you ask). That is where Celestron and Orion get their figure.
The second rule of thumb says that the maximum useful magnification
for any scope of whatever aperture is bounded, because of atmospheric
turbulence, to 250x or 300x (again, depending on whom you ask). That
is where Hardin gets its figure.

Even under average seeing, however, I would expect that a large scope
would still be able to use a higher magnification than a small scope;
it's just that the margin would be smaller.

Brian Tung
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