aperture vs. light pollution

I'm currently using an 8" SCT and am wondering if a 10" or 11" would be
worth the investment considering my city viewpoint. Will a larger aperture
penetrate a light polluted sky and see more objects, or just a brighter sky?

Chuck wrote:

I'm currently using an 8" SCT and am wondering if a 10" or 11" would be
worth the investment considering my city viewpoint. Will a larger aperture
penetrate a light polluted sky and see more objects, or just a brighter sky?


Generally Chuck, just more magnified light pollution....
Al is correct....

You can always substitute aperture with even more aperture;
but there is NO substitute for clear, dark, steady skies.
TW
PS- if all else fails, you can always invest in one of them
light pollution filters by Orion, and others.

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.
--
Jan
http://home.wanadoo.nl/jhm.vangastel/


"Chuck" schreef in bericht
...
I'm currently using an 8" SCT and am wondering if a 10" or 11" would be
worth the investment considering my city viewpoint. Will a larger
aperture
penetrate a light polluted sky and see more objects, or just a brighter
sky?

"Chuck" wrote in message
...
I'm currently using an 8" SCT and am wondering if a 10" or 11" would be
worth the investment considering my city viewpoint. Will a larger
aperture
penetrate a light polluted sky and see more objects, or just a brighter
sky?


Oh god not this foolishness again. Larger scope shows more in all light
pollution conditions period.



x-- 100 Proof News - http://www.100ProofNews.com
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"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

"GO VOLS!" wrote:

"Chuck" wrote in message
...
I'm currently using an 8" SCT and am wondering if a 10" or 11" would be
worth the investment considering my city viewpoint. Will a larger
aperture
penetrate a light polluted sky and see more objects, or just a brighter
sky?

Oh god not this foolishness again. Larger scope shows more in all light
pollution conditions period.

Not true. It depends on several factors, especially the characteristics
of the object. See Tony Flander's remarks for an experienced opinion.

Mike Simmons

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

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

In article ,
Stephen Paul wrote:

But it seems relatively fair to say that "for the vast majority of
objects visible in amateur telescopes" more aperture _is_ better.

Indeed true, since the vast majority of objects visible in amateur as
well as professional telescopes are faint stars and faint
galaxies.....

OTOH most sky observers enjoy observing a particular kind of
objects, not just the most common objects.... :-)

--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://www.stjarnhimlen.se/
http://home.tiscali.se/pausch/

Hi Stephen,

I don't mean to suggest that bigger isn't better when all other factors
are equal. I've been trying to dispel that myth for a long time. The
only problem occurs when the bigger scope has a focal length that is so
much longer that the "all other factors being equal" phrase that's
usually applied isn't applicable. If you can use the same magnification
(and FOV) then bigger is always better, in my experience. If an object
gets so big that it gets lost in the field, e.g., if it goes out of the
field leaving only inner, low-contrast portions in the field, then the
bigger scope can be worse. It's the same thing that happens when you're
enjoying a great view of M31 in big binoculars and then go to a scope
that only shows you a small portion of the galaxy that doesn't have
enough contrast features to be interesting (unless it's a really big
scope!). It's not that the bigger scope doesn't do as well, it's just
that it does something different that isn't as suited for a light
polluted sky on some objects, i.e., those features it shows might not
show up well against a bright background whereas the whole galaxy still
comes through with the binoculars.

To borrow from Tony's example, if I was going to observe the North
American Nebula in a light polluted sky I wouldn't choose a very large
light bucket that can't get below 200x. At least if it's dark I know I
can see some detail in the nebula that isn't visible in a smaller scope
(though not the whole thing) but in a light-polluted sky it's going to
be tough to see anything at all standing out from the bright background
if all that's in the FOV is a wisp fine detail. If it was possible to
have the larger scope and retain the magnification and FOV of the
smaller scope then that would be anyone's choice, light pollution or
not! I'm convinced it would *always* be better. But then you start
getting an exit pupil that's bigger than the entrance pupil of our own
optical system (the eye). Too bad we can't stuff all the light from the
entire field of the Keck into our eye.

I hope that makes sense. :-)

Mike Simmons

Stephen Paul wrote:

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