But it seems relatively fair to say that "for the vast majority of objects
visible in amateur telescopes" more aperture _is_ better. In particular, if
an object is visible in a smaller aperture under a given sky brightness,
then it should be more visible with larger aperture. It is those objects
that are not visible with the smaller aperture that are in question, and
these will invariably appear even better with larger under darker.

At least that's what I base my decision on. The ability to see better, those
that are visible, and those that are just detectable where I use my current
scope.

--
-Stephen Paul


"Mike Simmons" wrote in message
...
Tony,

You're the expert on observing under such conditions, AFAIC. I'd just
like to second your remarks based on some experience using small and
large telescopes under varying conditions of light pollution. Bigger is
generally better but light pollution can change the equation. The big
scopes are just not suited for some large, low-surface brightness
objects in light polluted conditions but generalizations (in generalg)
can't be made because there are several competing factors.

Mike Simmons

Tony Flanders wrote:

"Jan van Gastel" wrote in message
...

You will see more objects. But observing from a darker site will show
even
more then a 10 or 11 inch scope. Lets assume you observe under a sky
with
nakede eye limit 4.5 with an 8" scope. Traveling to a site with mag
5.5
naked eye limit, the 8 inch scope will show the same (faint) objects
as a
12.5 incher under mag 4.5 skies.

Actually, that is a best-case scenario; it overstates the benefits of
aperture. Or, more precisely, understates the benefits of dark skies.
The equation holds only for objects with very high surface brightness,
notably stars (including stars in clusters) and many planetary nebulae.
For objects where the limiting factor in visibility is low surface
brightness, including most galaxies, the benefit of the extra aperture
will be considerably less than that. In the extreme case, such as
M101, which is very large and has very low surface brightness, the
extra aperture probably won't help at all.

More to the point, the view in the 8" scope under mag 5.5 skies will
be *qualitatively* better than the view in the 11" scope under mag
4.5 skies. Most of the brighter galaxies and nebulae will be
visible in both conditions, but the smaller scope under darker
skies will show subtle features that are invisible under brighter
skies regardless of how much aperture you throw at them.

However, under identical skies, the 11" scope will usually perform
better than the 8" scope, often much better, and will only perform
worse in the fairly rare case of an object that doesn't fit into
the FOV of the larger scope, such as NGC 7000, the North America
Nebula.

- Tony Flanders