| |
Main
Date: 15 Dec 2006 02:31:35
From: Mike
Subject: C8 vs. C9.25
|
Is there a significant difference between these two?
The price is hundreds of dollars different and you need
a heavy duty mount for the 9.25. How much more
viewing would the 9.25 give you over the C8?
|
|
| |
Date: 14 Dec 2006 19:04:24
From: Uncle Bob
Subject: Re: C8 vs. C9.25
|
Mike wrote:
> Is there a significant difference between these two?
> The price is hundreds of dollars different and you need
> a heavy duty mount for the 9.25. How much more
> viewing would the 9.25 give you over the C8?
Without getting into technical details, I noticed that DSOs were
noticably brighter in the 9.25, and resolution in good seeing on Mars
was noticably better. Both were well-collimated examples of the scope.
I still own them both, because the 8" is lighter and shorter and
therefore a better grab-and-go scope. I use the 9.25 primarily for
astrophotography from home. The 8" could keep you visually entertained
for years, the 9.25" for perhaps a lifetime.
These are both very good scopes. If you use the 9.25" on an equatorial
mount, you will need to shim the rear cell a bit to align it with the
polar axis, because the rear cell casting is thinner than the corrector
plate cell. Causes the scope to point a tad high relative to the polar
axis of the mount, all other things being equal. No biggie, though.
Clear Skies,
Uncle Bob (TDY in Florida)
Fairfax, CA
|
| | |
Date: 15 Dec 2006 03:39:25
From: Mike
Subject: Re: C8 vs. C9.25
|
"Uncle Bob" <realonespam@bogusnet.net > wrote in message
news:1166151864.865143.74840@80g2000cwy.googlegroups.com...
> Mike wrote:
>> Is there a significant difference between these two?
>> The price is hundreds of dollars different and you need
>> a heavy duty mount for the 9.25. How much more
>> viewing would the 9.25 give you over the C8?
>
> Without getting into technical details, I noticed that DSOs were
> noticably brighter in the 9.25, and resolution in good seeing on Mars
> was noticably better. Both were well-collimated examples of the scope.
> I still own them both, because the 8" is lighter and shorter and
> therefore a better grab-and-go scope. I use the 9.25 primarily for
> astrophotography from home. The 8" could keep you visually entertained
> for years, the 9.25" for perhaps a lifetime.
> These are both very good scopes. If you use the 9.25" on an equatorial
> mount, you will need to shim the rear cell a bit to align it with the
> polar axis, because the rear cell casting is thinner than the corrector
> plate cell. Causes the scope to point a tad high relative to the polar
> axis of the mount, all other things being equal. No biggie, though.
>
Thanks Unca Bob . Your comment about a lifetime is very salemanship like.
Very powerful statement.
|
| | | |
Date: 15 Dec 2006 00:26:43
From: KLM
Subject: Re: C8 vs. C9.25
|
Mike wrote:
> "Uncle Bob" <realonespam@bogusnet.net> wrote in message
> news:1166151864.865143.74840@80g2000cwy.googlegroups.com...
> > Mike wrote:
> >> Is there a significant difference between these two?
> >> The price is hundreds of dollars different and you need
> >> a heavy duty mount for the 9.25. How much more
> >> viewing would the 9.25 give you over the C8?
> >
> > Without getting into technical details, I noticed that DSOs were
> > noticably brighter in the 9.25, and resolution in good seeing on Mars
> > was noticably better. Both were well-collimated examples of the scope.
> > I still own them both, because the 8" is lighter and shorter and
> > therefore a better grab-and-go scope. I use the 9.25 primarily for
> > astrophotography from home. The 8" could keep you visually entertained
> > for years, the 9.25" for perhaps a lifetime.
> > These are both very good scopes. If you use the 9.25" on an equatorial
> > mount, you will need to shim the rear cell a bit to align it with the
> > polar axis, because the rear cell casting is thinner than the corrector
> > plate cell. Causes the scope to point a tad high relative to the polar
> > axis of the mount, all other things being equal. No biggie, though.
> >
>
> Thanks Unca Bob . Your comment about a lifetime is very salemanship like.
> Very powerful statement.
They are fundamentally different sct's with the c9.25 being the better
by far.
|
| | |
Date: 18 Dec 2006 21:25:10
From: Marty
Subject: Re: C8 vs. C9.25
|
Uncle Bob was saying
>The 8" could keep you visually
> entertained for years, the 9.25" for
> perhaps a lifetime.
I can't comment on the 9.25, because I've never seen one. I'd expect a
bit of the usual trade-off between view and portability. However, my C8
has kept me entertained for 29 years now. :)
Marty
|
| |
Date: 15 Dec 2006 06:38:32
From: RMOLLISE
Subject: Re: C8 vs. C9.25
|
Hi:
Make that "slightly" different and "slightly" better.
At this point the Celestron optics that continue to impress me the most
are those in the C11s.
Peace,
Rod Mollise
Author of:
Choosing and Using a Schmidt Cassegrain Telescope
and
The Urban Astronomer's Guide
<http://skywatch.brainiac.com/astroland >
KLM wrote:
>
> They are fundamentally different sct's with the c9.25 being the better
> by far.
|
| |
Date: 15 Dec 2006 10:05:31
From: Roger Hamlett
Subject: Re: C8 vs. C9.25
|
"Mike" <mike@yahoo.net > wrote in message
news:bOngh.74948$hn.73593@edtnps82...
> Is there a significant difference between these two?
> The price is hundreds of dollars different and you need
> a heavy duty mount for the 9.25. How much more
> viewing would the 9.25 give you over the C8?
They are very different.
In light terms, just 33% more collected light. However the C9.25, is an
'unusual' SCT. It uses a slower primary mirror, and less magnification on
the secondary than most 'normal' SCT's. This gives a flatter field (makes
stars look better focussed across the view), and reduces some of the
slight chromatic aberrations that are present in an SCT. The big downside,
is that the OTA, is nearly as heavy as a C11.
The C9.25, is a very nice scope. The C8, is not 'bad' (don't think this),
but the C9.25, just gives views that look 'better'.
Best Wishes
|
| | |
Date: 15 Dec 2006 14:10:24
From: Mike
Subject: Re: C8 vs. C9.25
|
"Roger Hamlett" <rogerspamignored@ttelmah.demon.co.uk > wrote in message
news:Lrugh.1985$v4.1329@newsfe3-win.ntli.net...
>
> "Mike" <mike@yahoo.net> wrote in message
> news:bOngh.74948$hn.73593@edtnps82...
>> Is there a significant difference between these two?
>> The price is hundreds of dollars different and you need
>> a heavy duty mount for the 9.25. How much more
>> viewing would the 9.25 give you over the C8?
> They are very different.
> In light terms, just 33% more collected light. However the C9.25, is an
> 'unusual' SCT. It uses a slower primary mirror, and less magnification on
> the secondary than most 'normal' SCT's. This gives a flatter field (makes
> stars look better focussed across the view), and reduces some of the
> slight chromatic aberrations that are present in an SCT. The big downside,
> is that the OTA, is nearly as heavy as a C11.
> The C9.25, is a very nice scope. The C8, is not 'bad' (don't think this),
> but the C9.25, just gives views that look 'better'.
>
> Best Wishes
I suppose the new caarbon fiber OTA's make it lighter. Thanks
|
| | | |
Date: 15 Dec 2006 15:37:50
From: Roger Hamlett
Subject: Re: C8 vs. C9.25
|
"Mike" <mike@yahoo.net > wrote in message
news:k1ygh.66213$YV4.63908@edtnps89...
>
> "Roger Hamlett" <rogerspamignored@ttelmah.demon.co.uk> wrote in message
> news:Lrugh.1985$v4.1329@newsfe3-win.ntli.net...
>>
>> "Mike" <mike@yahoo.net> wrote in message
>> news:bOngh.74948$hn.73593@edtnps82...
>>> Is there a significant difference between these two?
>>> The price is hundreds of dollars different and you need
>>> a heavy duty mount for the 9.25. How much more
>>> viewing would the 9.25 give you over the C8?
>> They are very different.
>> In light terms, just 33% more collected light. However the C9.25, is an
>> 'unusual' SCT. It uses a slower primary mirror, and less magnification
>> on the secondary than most 'normal' SCT's. This gives a flatter field
>> (makes stars look better focussed across the view), and reduces some of
>> the slight chromatic aberrations that are present in an SCT. The big
>> downside, is that the OTA, is nearly as heavy as a C11.
>> The C9.25, is a very nice scope. The C8, is not 'bad' (don't think
>> this), but the C9.25, just gives views that look 'better'.
>>
>> Best Wishes
>
> I suppose the new caarbon fiber OTA's make it lighter. Thanks
New?.
Not a lot. The carbon OTA units weigh about the same as their aluminium
tubed cousins. The advantage is stability with temperature changes. The
downside is slower cooldown.
Best Wishes
|
| |
Date: 15 Dec 2006 11:46:59
From: RMOLLISE
Subject: Re: C8 vs. C9.25
|
Roger Hamlett wrote:
> "Mike" <mike@yahoo.net> wrote in message
> news:k1ygh.66213$YV4.63908@edtnps89...
> New?.
> Not a lot. The carbon OTA units weigh about the same as their aluminium
> tubed cousins. The advantage is stability with temperature changes. The
> downside is slower cooldown.
Yep..and that advantage is mainly of interest to serious imagers...
Peace,
Rod Mollise
Author of:
Choosing and Using a Schmidt Cassegrain Telescope
and
The Urban Astronomer's Guide
<http://skywatch.brainiac.com/astroland >
|
| | |
Date: 15 Dec 2006 23:04:18
From: Mike
Subject: Re: C8 vs. C9.25
|
"RMOLLISE" <rmollise@hotmail.com > wrote in message
news:1166212019.074959.4200@n67g2000cwd.googlegroups.com...
>
> Roger Hamlett wrote:
>> "Mike" <mike@yahoo.net> wrote in message
>> news:k1ygh.66213$YV4.63908@edtnps89...
>> New?.
>> Not a lot. The carbon OTA units weigh about the same as their aluminium
>> tubed cousins. The advantage is stability with temperature changes. The
>> downside is slower cooldown.
>
>
> Yep..and that advantage is mainly of interest to serious imagers...
>
As in rich people?
|
| |
Date: 16 Dec 2006 07:27:40
From: RMOLLISE
Subject: Re: C8 vs. C9.25
|
Mike wrote:
> "RMOLLISE" <rmollise@hotmail.com> wrote in message
> news:1166212019.074959.4200@n67g2000cwd.googlegroups.com...
> >
> > Roger Hamlett wrote:
> >> "Mike" <mike@yahoo.net> wrote in message
> >> news:k1ygh.66213$YV4.63908@edtnps89...
> >> New?.
> >> Not a lot. The carbon OTA units weigh about the same as their aluminium
> >> tubed cousins. The advantage is stability with temperature changes. The
> >> downside is slower cooldown.
> >
> >
> > Yep..and that advantage is mainly of interest to serious imagers...
> >
>
>
> As in rich people?
Not as I, sitting in the comfortable venue of "middle age," define
"rich". ;-)
You can get a purty derned serious camera for about 3000 US$ right now.
I know people who spend a lot more than that on 4-wheelers to help them
go out and shoot at Bambi (usually without success) once or twice a
year. ;-)
Peace,
Rod Mollise
Author of:
Choosing and Using a Schmidt Cassegrain Telescope
and
The Urban Astronomer's Guide
<http://skywatch.brainiac.com/astroland >
|
| | |
Date: 16 Dec 2006 17:43:53
From: Mike
Subject: Re: C8 vs. C9.25
|
"RMOLLISE" <rmollise@hotmail.com > wrote in message
news:1166282859.909749.131120@f1g2000cwa.googlegroups.com...
>
> Mike wrote:
>> "RMOLLISE" <rmollise@hotmail.com> wrote in message
>> news:1166212019.074959.4200@n67g2000cwd.googlegroups.com...
>> >
>> > Roger Hamlett wrote:
>> >> "Mike" <mike@yahoo.net> wrote in message
>> >> news:k1ygh.66213$YV4.63908@edtnps89...
>> >> New?.
>> >> Not a lot. The carbon OTA units weigh about the same as their
>> >> aluminium
>> >> tubed cousins. The advantage is stability with temperature changes.
>> >> The
>> >> downside is slower cooldown.
>> >
>> >
>> > Yep..and that advantage is mainly of interest to serious imagers...
>> >
>>
>>
>> As in rich people?
>
> Not as I, sitting in the comfortable venue of "middle age," define
> "rich". ;-)
>
> You can get a purty derned serious camera for about 3000 US$ right now.
> I know people who spend a lot more than that on 4-wheelers to help them
> go out and shoot at Bambi (usually without success) once or twice a
> year. ;-)
>
Come on!! A camera for 3000 US ?? You mean SBIGS..right? I guess the
lowly Rebel XTi doesn't
qualify as "serious".
|
| |
Date: 16 Dec 2006 13:45:46
From: RMOLLISE
Subject: Re: C8 vs. C9.25
|
Mike wrote:
>
>
> Come on!! A camera for 3000 US ?? You mean SBIGS..right? I guess the
> lowly Rebel XTi doesn't
> qualify as "serious".
Hi Mike:
Did I say that? If so, quote me on it.
The Rebel XT can do a fine job imaging, but, no, it would probably not
be the choice of a "serious" imager, whatever that is. A cooled CCD
chip equipped camera is stil best for deep sky imaging. Also, 3K isn't
really a whole lot when you consider what a camera in this class
would've cost 5 years back.
If you are happy with your Rebel, and are serious about imaging, that
does indeed make you a serious imager--or whatever you might want to be
as far as I'm concerned. :-)
Peace,
Rod Mollise
Author of:
Choosing and Using a Schmidt Cassegrain Telescope
and
The Urban Astronomer's Guide
<http://skywatch.brainiac.com/astroland >
|
| |
Date: 17 Dec 2006 16:20:46
From: RMOLLISE
Subject: Re: C8 vs. C9.25
|
Yep. Despite my larger CATs, my most used SCT? Still the good, old C8.
;-)
Rich wrote:
But, the weight increase is
> considerable, so take
> that into account. If you take your 8" outside 25% more often because
> of weight, then
> it could be the best choice.
|
| |
Date: 17 Dec 2006 10:24:46
From: Rich
Subject: Re: C8 vs. C9.25
|
Mike wrote:
> Is there a significant difference between these two?
> The price is hundreds of dollars different and you need
> a heavy duty mount for the 9.25. How much more
> viewing would the 9.25 give you over the C8?
Depending on where you live, it could make a significant difference.
Extra aperture
is always better. You might be straining to see stars in a global
cluster in the C8
and easily see them in the 9.25." But, the weight increase is
considerable, so take
that into account. If you take your 8" outside 25% more often because
of weight, then
it could be the best choice.
|
| | |
Date: 18 Dec 2006 19:59:49
From: AstroApp
Subject: Re: C8 vs. C9.25
|
On 17 Dec 2006 10:24:46 -0800, "Rich" <rander3127@gmail.com > wrote:
>Mike wrote:
>> Is there a significant difference between these two?
>> The price is hundreds of dollars different and you need
>> a heavy duty mount for the 9.25. How much more
>> viewing would the 9.25 give you over the C8?
>
>Depending on where you live, it could make a significant difference.
>Extra aperture is always better. You might be straining to see stars in a global
>cluster in the C8 and easily see them in the 9.25."
I wonder if I can possibly agree with the last statement. There is
not a huge difference WRT to resolution and light gathering compared
to the relationship between an 8 and a 10 or 11 inch scope.
Generally using the accepted formulae for comparison, one comes up
with some fairly reasonable numbers:
8 inch:
light gathering 843 times the human eye
Dawes limit 0.57 arcseconds
Stellar magnitude limit: averages around 13.5
9.25 inch:
light gathering 1127x
Dawes limit 0.49 arcseconds
Stellar magnitude limit: perhaps around 13.8
You can go deeper in stellar magnitude limit by removing the star
diagonal, adjusting the magnification, and if your own experience in
detecting stars might be better than average; my experience tends to
suggest that it is possible that an 8" SCT with critically sharp,
focused optics COULD reach (under absolutely breathtakingly perfect
seeing, with clean, ultra-coated, brand new optics, by a fairly young
observer with exquisite eyesight) about 15th magnitude; with the same
criteria a 9.25 inch SCT could perhaps reach 15.4: this is by using
the best limiting magnitude calculator I know of, which is here:
http://www.go.ednet.ns.ca/~larry/astro/maglimit.html
Now in both cases, the difference in stellar magnitude limit is either
0.3, or 0.4. That would mean that some of the fainter outlying stars
in the brighter, large diameter globulars would not always be
detectable in the 8 while they WERE just barely visible in the 9.25,
everything else being equal. The resolution difference is not huge so
the ultimate difference of discerning individual stars won't be nearly
as great between the 8 and the 9.25 as when comparing an 8 to a 10 or
11 or 12.
Then, there's the issue of the central obstruction and whether we're
comparing f/10 to f/10, or f/6 to f/10 Schmidt Cassegrains, etc etc.
However, IMO based on comparing my 8, 10, and 11 inch scopes, I wonder
if it is a quantifiable statement we'd all agree on that, quoting you,
"You might be straining to see stars in a global [sic] cluster in the
C8 and easily see them in the 9.25."
Generally, one is almost always "straining" to see the stars of
globular clusters as individual stellar points in an 8" scope,
especially a reflector (it's easier in say a 7" APO refractor, or
sometimes even in a *6* inch APO...) Aside from, say, M3, M5, or M13,
and maybe M22 if it's up high enough, the resolution of 8 or 9.25"
scopes and their light gathering and limiting magnitude are really not
optimal for "going inside" a globular cluster; larger scopes are much
better.
See this page for a comparison (I agree with the depictions here based
on experience with various scopes I've owned and used):
http://www.obsessiontelescopes.com/m13/index.html
The only caveat here is the in order for the fainter stars to show up
in a fairly good brightness relation with the stars shown by the
larger apertures, the brightness is scaled so that you CAN see a
difference: but it's not the REAL difference since the screen of your
typical monitor cannot produce the luminance of the large scopes nor
the true dynamic range; and the monitor's background raster is
brighter than the visual background in an eyepiece, in a very dark
sky.
It's often next to impossible to do a good, accurate comparison even
at a star party with representative scopes available, but in lieu of
that, I'd suggest doing a little observing, if possible, with an 8 and
a 9.25 over time, to get a concept of a "baseline". I've done that
and in my opinion, a 9.25 is not a "huge leap" above an 8, all things
being equal. The brightness and resolution improvement do not knock
your socks off. Even in my 11, globulars don't do that. But on a 17
inch scope: they DO.
AstroApp
|
| | | |
Date: 19 Dec 2006 16:36:12
From: Mike
Subject: Re: C8 vs. C9.25
|
Excellent point of view. I think a Meade 10" is a nice mid-range way to
go.
"AstroApp" <AstroApp@blocked.net > wrote in message
news:fqsdo2583nub77l1c4s6k6fs21a697vnd3@4ax.com...
> On 17 Dec 2006 10:24:46 -0800, "Rich" <rander3127@gmail.com> wrote:
>>Mike wrote:
>>> Is there a significant difference between these two?
>>> The price is hundreds of dollars different and you need
>>> a heavy duty mount for the 9.25. How much more
>>> viewing would the 9.25 give you over the C8?
>>
>>Depending on where you live, it could make a significant difference.
>>Extra aperture is always better. You might be straining to see stars in a
>>global
>>cluster in the C8 and easily see them in the 9.25."
>
> I wonder if I can possibly agree with the last statement. There is
> not a huge difference WRT to resolution and light gathering compared
> to the relationship between an 8 and a 10 or 11 inch scope.
>
> Generally using the accepted formulae for comparison, one comes up
> with some fairly reasonable numbers:
>
> 8 inch:
> light gathering 843 times the human eye
> Dawes limit 0.57 arcseconds
> Stellar magnitude limit: averages around 13.5
>
> 9.25 inch:
> light gathering 1127x
> Dawes limit 0.49 arcseconds
> Stellar magnitude limit: perhaps around 13.8
>
> You can go deeper in stellar magnitude limit by removing the star
> diagonal, adjusting the magnification, and if your own experience in
> detecting stars might be better than average; my experience tends to
> suggest that it is possible that an 8" SCT with critically sharp,
> focused optics COULD reach (under absolutely breathtakingly perfect
> seeing, with clean, ultra-coated, brand new optics, by a fairly young
> observer with exquisite eyesight) about 15th magnitude; with the same
> criteria a 9.25 inch SCT could perhaps reach 15.4: this is by using
> the best limiting magnitude calculator I know of, which is here:
> http://www.go.ednet.ns.ca/~larry/astro/maglimit.html
>
> Now in both cases, the difference in stellar magnitude limit is either
> 0.3, or 0.4. That would mean that some of the fainter outlying stars
> in the brighter, large diameter globulars would not always be
> detectable in the 8 while they WERE just barely visible in the 9.25,
> everything else being equal. The resolution difference is not huge so
> the ultimate difference of discerning individual stars won't be nearly
> as great between the 8 and the 9.25 as when comparing an 8 to a 10 or
> 11 or 12.
>
> Then, there's the issue of the central obstruction and whether we're
> comparing f/10 to f/10, or f/6 to f/10 Schmidt Cassegrains, etc etc.
>
> However, IMO based on comparing my 8, 10, and 11 inch scopes, I wonder
> if it is a quantifiable statement we'd all agree on that, quoting you,
> "You might be straining to see stars in a global [sic] cluster in the
> C8 and easily see them in the 9.25."
>
> Generally, one is almost always "straining" to see the stars of
> globular clusters as individual stellar points in an 8" scope,
> especially a reflector (it's easier in say a 7" APO refractor, or
> sometimes even in a *6* inch APO...) Aside from, say, M3, M5, or M13,
> and maybe M22 if it's up high enough, the resolution of 8 or 9.25"
> scopes and their light gathering and limiting magnitude are really not
> optimal for "going inside" a globular cluster; larger scopes are much
> better.
>
> See this page for a comparison (I agree with the depictions here based
> on experience with various scopes I've owned and used):
> http://www.obsessiontelescopes.com/m13/index.html
>
> The only caveat here is the in order for the fainter stars to show up
> in a fairly good brightness relation with the stars shown by the
> larger apertures, the brightness is scaled so that you CAN see a
> difference: but it's not the REAL difference since the screen of your
> typical monitor cannot produce the luminance of the large scopes nor
> the true dynamic range; and the monitor's background raster is
> brighter than the visual background in an eyepiece, in a very dark
> sky.
>
> It's often next to impossible to do a good, accurate comparison even
> at a star party with representative scopes available, but in lieu of
> that, I'd suggest doing a little observing, if possible, with an 8 and
> a 9.25 over time, to get a concept of a "baseline". I've done that
> and in my opinion, a 9.25 is not a "huge leap" above an 8, all things
> being equal. The brightness and resolution improvement do not knock
> your socks off. Even in my 11, globulars don't do that. But on a 17
> inch scope: they DO.
>
> AstroApp
>
>
|
| | | | |
Date: 19 Dec 2006 08:52:16
From: Mij Adyaw
Subject: Re: C8 vs. C9.25
|
I have heard that the C9.25 is optically better than the Meade 10 inch. I
have never owned a Meade 10 inch, but currently own a C9.25 and it is
optically very good.
"Mike" <mike@yahoo.net > wrote in message
news:0yUhh.90407$rv4.84463@edtnps90...
>
> Excellent point of view. I think a Meade 10" is a nice mid-range way to
> go.
>
>
> "AstroApp" <AstroApp@blocked.net> wrote in message
> news:fqsdo2583nub77l1c4s6k6fs21a697vnd3@4ax.com...
>> On 17 Dec 2006 10:24:46 -0800, "Rich" <rander3127@gmail.com> wrote:
>>>Mike wrote:
>>>> Is there a significant difference between these two?
>>>> The price is hundreds of dollars different and you need
>>>> a heavy duty mount for the 9.25. How much more
>>>> viewing would the 9.25 give you over the C8?
>>>
>>>Depending on where you live, it could make a significant difference.
>>>Extra aperture is always better. You might be straining to see stars in
>>>a global
>>>cluster in the C8 and easily see them in the 9.25."
>>
>> I wonder if I can possibly agree with the last statement. There is
>> not a huge difference WRT to resolution and light gathering compared
>> to the relationship between an 8 and a 10 or 11 inch scope.
>>
>> Generally using the accepted formulae for comparison, one comes up
>> with some fairly reasonable numbers:
>>
>> 8 inch:
>> light gathering 843 times the human eye
>> Dawes limit 0.57 arcseconds
>> Stellar magnitude limit: averages around 13.5
>>
>> 9.25 inch:
>> light gathering 1127x
>> Dawes limit 0.49 arcseconds
>> Stellar magnitude limit: perhaps around 13.8
>>
>> You can go deeper in stellar magnitude limit by removing the star
>> diagonal, adjusting the magnification, and if your own experience in
>> detecting stars might be better than average; my experience tends to
>> suggest that it is possible that an 8" SCT with critically sharp,
>> focused optics COULD reach (under absolutely breathtakingly perfect
>> seeing, with clean, ultra-coated, brand new optics, by a fairly young
>> observer with exquisite eyesight) about 15th magnitude; with the same
>> criteria a 9.25 inch SCT could perhaps reach 15.4: this is by using
>> the best limiting magnitude calculator I know of, which is here:
>> http://www.go.ednet.ns.ca/~larry/astro/maglimit.html
>>
>> Now in both cases, the difference in stellar magnitude limit is either
>> 0.3, or 0.4. That would mean that some of the fainter outlying stars
>> in the brighter, large diameter globulars would not always be
>> detectable in the 8 while they WERE just barely visible in the 9.25,
>> everything else being equal. The resolution difference is not huge so
>> the ultimate difference of discerning individual stars won't be nearly
>> as great between the 8 and the 9.25 as when comparing an 8 to a 10 or
>> 11 or 12.
>>
>> Then, there's the issue of the central obstruction and whether we're
>> comparing f/10 to f/10, or f/6 to f/10 Schmidt Cassegrains, etc etc.
>>
>> However, IMO based on comparing my 8, 10, and 11 inch scopes, I wonder
>> if it is a quantifiable statement we'd all agree on that, quoting you,
>> "You might be straining to see stars in a global [sic] cluster in the
>> C8 and easily see them in the 9.25."
>>
>> Generally, one is almost always "straining" to see the stars of
>> globular clusters as individual stellar points in an 8" scope,
>> especially a reflector (it's easier in say a 7" APO refractor, or
>> sometimes even in a *6* inch APO...) Aside from, say, M3, M5, or M13,
>> and maybe M22 if it's up high enough, the resolution of 8 or 9.25"
>> scopes and their light gathering and limiting magnitude are really not
>> optimal for "going inside" a globular cluster; larger scopes are much
>> better.
>>
>> See this page for a comparison (I agree with the depictions here based
>> on experience with various scopes I've owned and used):
>> http://www.obsessiontelescopes.com/m13/index.html
>>
>> The only caveat here is the in order for the fainter stars to show up
>> in a fairly good brightness relation with the stars shown by the
>> larger apertures, the brightness is scaled so that you CAN see a
>> difference: but it's not the REAL difference since the screen of your
>> typical monitor cannot produce the luminance of the large scopes nor
>> the true dynamic range; and the monitor's background raster is
>> brighter than the visual background in an eyepiece, in a very dark
>> sky.
>>
>> It's often next to impossible to do a good, accurate comparison even
>> at a star party with representative scopes available, but in lieu of
>> that, I'd suggest doing a little observing, if possible, with an 8 and
>> a 9.25 over time, to get a concept of a "baseline". I've done that
>> and in my opinion, a 9.25 is not a "huge leap" above an 8, all things
>> being equal. The brightness and resolution improvement do not knock
>> your socks off. Even in my 11, globulars don't do that. But on a 17
>> inch scope: they DO.
>>
>> AstroApp
>>
>>
>
>
|
| | | |
Date: 19 Dec 2006 09:43:30
From: Joe Bergeron
Subject: Re: C8 vs. C9.25
|
Quit making so much sense! This is SAA, you know!
--
Joe Bergeron
http://www.joebergeron.com
|
|
