Should I change scopes to accommodate poor seeing?

Hello Group,

After reading through the archives and other sources about the
relationship between aperture, optical quality, scope design and
vulnerability to seeing conditions, I'm asking for opinions about my
next move.

I'm primarily into visual planetary, lunar and doubles work. I've got
a well-collimated C9.25 with at least good optics (based on star test
and images during fleeting moments of still air). I keep the scope in
an unheated garage, so it reaches thermal equilibrium fairly quickly.

Here's the problem: I live in southeast Wisconsin and the seeing is
usually poor. I'm at a relatively dark site, and I have my share of
clear cold nights, but 9 times out of 10, the atmosphere is just
boiling. (Why they decided to put the world's largest refractor in
the Yerkes Observatory at Williams Bay is beyond me.) The seeing
rarely supports magnification beyond about 200x (12mm ortho).

I've tried an off-axis mask to reduce the effective aperture (and to
eliminate the effects on contrast of a central obstruction), but the
image is dreadfully dim. I also realize that I'm losing resolving
power with the mask.

I'm thinking about going to a smaller scope to reduce the negative
effects of poor seeing. Given the generally deleterious effects of a
central obstruction, and further assuming that fewer optical surfaces
means fewer opportunities for error, I'm thinking of a refractor in
the 4 to 6-inch range. Because my work usually calls for high
magnification, I'm thinking a slow achromat (f/10, f/15, higher?)
might work for me. Perhaps an apochromat and a good barlow (though my
funds are limited). Portability is not an issue as I'm planning a
permanent installation eventually.

So, what would you do if you were me? I'm not expecting definitive
answers, but rather opinions/solutions for my particular situation.

Thanks in advance.

Dave

On 18 Feb 2004 12:38:59 -0800, (Dave
Bohnsack) wrote:

snip .

I'm thinking about going to a smaller scope to reduce the negative
effects of poor seeing.

Dave, larger aperture does not add to the negative effects of poor
seeing; rather, poor seeing just keeps a larger instrument from
realizing its full potential. Assuming equivalent optics, and
magnification factor, over time a larger aperture will *always*
outperform a smaller. You will have to wait longer for those magic
moments when seeing crystallizes, but when they occur you'll be
rewarded with a better view.

Of course, replacing the SCT with an 8" APO is another thing
altogether grin

Wayne Hoffman
33° 49" 17' N 117° 56" 41' W
"Don't Look Down"

http://home.pacbell.net/w6wlr/

On 18 Feb 2004 12:38:59 -0800, (Dave
Bohnsack) wrote:

snip .

I'm thinking about going to a smaller scope to reduce the negative
effects of poor seeing.

Dave, larger aperture does not add to the negative effects of poor
seeing; rather, poor seeing just keeps a larger instrument from
realizing its full potential. Assuming equivalent optics, and
magnification factor, over time a larger aperture will *always*
outperform a smaller. You will have to wait longer for those magic
moments when seeing crystallizes, but when they occur you'll be
rewarded with a better view.

Of course, replacing the SCT with an 8" APO is another thing
altogether grin

Wayne Hoffman
33° 49" 17' N 117° 56" 41' W
"Don't Look Down"

http://home.pacbell.net/w6wlr/

So, what would you do if you were me? I'm not expecting definitive
answers, but rather opinions/solutions for my particular situation.


Hi:

Stick with the larger scope. Seeing almost always settles down occasionally,
and when it does you will see far more than you will with a stopped down or
smaller instrument.

Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
Like SCTs and MCTs?
Check-out sct-user, the mailing list for CAT fanciers!
Goto http://members.aol.com/RMOLLISE/index.html

So, what would you do if you were me? I'm not expecting definitive
answers, but rather opinions/solutions for my particular situation.


Hi:

Stick with the larger scope. Seeing almost always settles down occasionally,
and when it does you will see far more than you will with a stopped down or
smaller instrument.

Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
Like SCTs and MCTs?
Check-out sct-user, the mailing list for CAT fanciers!
Goto http://members.aol.com/RMOLLISE/index.html

Dave,

A smaller telescope isn't going to perform better than the larger one
based on seeing alone. The best it can do is match the larger one.
Unless you have problems with thermal equilibration, portability or
something else related to the size of the telescope -- and you say there
aren't any such factors -- there's no disadvantage to the larger
telescope. As has been pointed out already, there are times that you'll
get better seeing that the larger telescope can take advantage of. And
even when the seeing isn't that great there are times when the larger
scope does better anyway, at least part of the time.

(Why they decided to put the world's largest refractor in
the Yerkes Observatory at Williams Bay is beyond me.)

I know this was a tongue-in-cheek remark but I'm going to answer
anyway... :-)

George Ellery Hale, the founder and first director of Yerkes Observatory,
was in Chicago and so was his backer, Charles Yerkes. The 40-inch lens
was originally made for a telescope to be placed on Mount Wilson in
southern California but a real estate bust and the death of the primary
donor killed that idea. When Hale acquired it he was contacted by people
in LA about building the telescope in southern California but he said it
was too far away to consider. But when the Carnegie Institution of
Washington announced plans to establish a new observatory just five years
later he was out to southern California in a hurry, and established the
Mount Wilson Solar Observatory there in 1903. He described himself as a
"sun worshipper" but no one's sure if that's because he was a solar
astronomer or because he preferred the weather in southern California to
the weather in southern Wisconsin.

Mike Simmons

Dave,

A smaller telescope isn't going to perform better than the larger one
based on seeing alone. The best it can do is match the larger one.
Unless you have problems with thermal equilibration, portability or
something else related to the size of the telescope -- and you say there
aren't any such factors -- there's no disadvantage to the larger
telescope. As has been pointed out already, there are times that you'll
get better seeing that the larger telescope can take advantage of. And
even when the seeing isn't that great there are times when the larger
scope does better anyway, at least part of the time.

(Why they decided to put the world's largest refractor in
the Yerkes Observatory at Williams Bay is beyond me.)

I know this was a tongue-in-cheek remark but I'm going to answer
anyway... :-)

George Ellery Hale, the founder and first director of Yerkes Observatory,
was in Chicago and so was his backer, Charles Yerkes. The 40-inch lens
was originally made for a telescope to be placed on Mount Wilson in
southern California but a real estate bust and the death of the primary
donor killed that idea. When Hale acquired it he was contacted by people
in LA about building the telescope in southern California but he said it
was too far away to consider. But when the Carnegie Institution of
Washington announced plans to establish a new observatory just five years
later he was out to southern California in a hurry, and established the
Mount Wilson Solar Observatory there in 1903. He described himself as a
"sun worshipper" but no one's sure if that's because he was a solar
astronomer or because he preferred the weather in southern California to
the weather in southern Wisconsin.

Mike Simmons

Dave, I'm familiar with your area - my brother lives at Appelton. Ive
viewed
all over Wisc from Dubuque to Madison then east to your area, north
beyond Appelton to Manitowac, Green Bay, up to Gladstone (on Mackinack)
then into Ont thru the Sioux both east and west around the horn back
down to GrandMarais, Duluth, etc...

I'd hate to see you get rid of a C9.25 especially if its a good one, so
lets hold off
on that. Im surprised masking didnt help a little but I understand you
dont want to
sacrifice brightness or resolution. You prefer both. In addition, you
would like some
ability to magnify even under turbulence ... I know what you're after and
the conditions
you work under. Ive been there myself.

I wont even into this issue concerning aperture and turbulence suffiice it
to say there
is a theoretical side people gnerally speak from saying AP always wins,
then there is
the practical side. The practical side always seems to win out in your
situation and
the problem the theorist just cant comprehend is, under conditions with
few steady
days per year, one just never gets to the theoretical side to prove the
theoretical
side ... and the phrase: "You cant roller skate in a buffalo herd" comes
straight to
mind.

I always hauled a mn61 or a good 5" refractor or a good f/7-f/8 8"
newtonian
along on my expeditions to you neck-o-the woods. Make the rounds of your
friends in area clubs and try theirs udner the same conditions, ask about
their
experiences right in your area, then make your decision. But I would not
get rid
of your c9.25 unless you have an over-riding reason to do it. Im thinking
there
are a few around you who use an mn61, 5" f/8+ refractor, or 8" f/7 newt to

cope with the unsettled air. ??? Ask around your area. The scopes I
mention
were my solution to the problem in medium aperture while the big dob got
left
in the van. You have some excellent clubs around you - make use of them.

Good luck -
Jerry







Dave Bohnsack wrote:

Hello Group,

After reading through the archives and other sources about the
relationship between aperture, optical quality, scope design and
vulnerability to seeing conditions, I'm asking for opinions about my
next move.

I'm primarily into visual planetary, lunar and doubles work. I've got
a well-collimated C9.25 with at least good optics (based on star test
and images during fleeting moments of still air). I keep the scope in
an unheated garage, so it reaches thermal equilibrium fairly quickly.

Here's the problem: I live in southeast Wisconsin and the seeing is
usually poor. I'm at a relatively dark site, and I have my share of
clear cold nights, but 9 times out of 10, the atmosphere is just
boiling. (Why they decided to put the world's largest refractor in
the Yerkes Observatory at Williams Bay is beyond me.) The seeing
rarely supports magnification beyond about 200x (12mm ortho).

I've tried an off-axis mask to reduce the effective aperture (and to
eliminate the effects on contrast of a central obstruction), but the
image is dreadfully dim. I also realize that I'm losing resolving
power with the mask.

I'm thinking about going to a smaller scope to reduce the negative
effects of poor seeing. Given the generally deleterious effects of a
central obstruction, and further assuming that fewer optical surfaces
means fewer opportunities for error, I'm thinking of a refractor in
the 4 to 6-inch range. Because my work usually calls for high
magnification, I'm thinking a slow achromat (f/10, f/15, higher?)
might work for me. Perhaps an apochromat and a good barlow (though my
funds are limited). Portability is not an issue as I'm planning a
permanent installation eventually.

So, what would you do if you were me? I'm not expecting definitive
answers, but rather opinions/solutions for my particular situation.

Thanks in advance.

Dave

Dave, I'm familiar with your area - my brother lives at Appelton. Ive
viewed
all over Wisc from Dubuque to Madison then east to your area, north
beyond Appelton to Manitowac, Green Bay, up to Gladstone (on Mackinack)
then into Ont thru the Sioux both east and west around the horn back
down to GrandMarais, Duluth, etc...

I'd hate to see you get rid of a C9.25 especially if its a good one, so
lets hold off
on that. Im surprised masking didnt help a little but I understand you
dont want to
sacrifice brightness or resolution. You prefer both. In addition, you
would like some
ability to magnify even under turbulence ... I know what you're after and
the conditions
you work under. Ive been there myself.

I wont even into this issue concerning aperture and turbulence suffiice it
to say there
is a theoretical side people gnerally speak from saying AP always wins,
then there is
the practical side. The practical side always seems to win out in your
situation and
the problem the theorist just cant comprehend is, under conditions with
few steady
days per year, one just never gets to the theoretical side to prove the
theoretical
side ... and the phrase: "You cant roller skate in a buffalo herd" comes
straight to
mind.

I always hauled a mn61 or a good 5" refractor or a good f/7-f/8 8"
newtonian
along on my expeditions to you neck-o-the woods. Make the rounds of your
friends in area clubs and try theirs udner the same conditions, ask about
their
experiences right in your area, then make your decision. But I would not
get rid
of your c9.25 unless you have an over-riding reason to do it. Im thinking
there
are a few around you who use an mn61, 5" f/8+ refractor, or 8" f/7 newt to

cope with the unsettled air. ??? Ask around your area. The scopes I
mention
were my solution to the problem in medium aperture while the big dob got
left
in the van. You have some excellent clubs around you - make use of them.

Good luck -
Jerry







Dave Bohnsack wrote:

Hello Group,

After reading through the archives and other sources about the
relationship between aperture, optical quality, scope design and
vulnerability to seeing conditions, I'm asking for opinions about my
next move.

I'm primarily into visual planetary, lunar and doubles work. I've got
a well-collimated C9.25 with at least good optics (based on star test
and images during fleeting moments of still air). I keep the scope in
an unheated garage, so it reaches thermal equilibrium fairly quickly.

Here's the problem: I live in southeast Wisconsin and the seeing is
usually poor. I'm at a relatively dark site, and I have my share of
clear cold nights, but 9 times out of 10, the atmosphere is just
boiling. (Why they decided to put the world's largest refractor in
the Yerkes Observatory at Williams Bay is beyond me.) The seeing
rarely supports magnification beyond about 200x (12mm ortho).

I've tried an off-axis mask to reduce the effective aperture (and to
eliminate the effects on contrast of a central obstruction), but the
image is dreadfully dim. I also realize that I'm losing resolving
power with the mask.

I'm thinking about going to a smaller scope to reduce the negative
effects of poor seeing. Given the generally deleterious effects of a
central obstruction, and further assuming that fewer optical surfaces
means fewer opportunities for error, I'm thinking of a refractor in
the 4 to 6-inch range. Because my work usually calls for high
magnification, I'm thinking a slow achromat (f/10, f/15, higher?)
might work for me. Perhaps an apochromat and a good barlow (though my
funds are limited). Portability is not an issue as I'm planning a
permanent installation eventually.

So, what would you do if you were me? I'm not expecting definitive
answers, but rather opinions/solutions for my particular situation.

Thanks in advance.

Dave

Dave

I agree with the rest of the group. Id keep the 9.25. It has a very
good reputation and will give you your moneys worth when you get good
seeing.

As far a second scope as a quick look scope id go with a C-102
refractor or perhaps a 5" refractor especially if your 9.25 is on a
GEM. You can pop the 9.25 off and put the refractor OTA on. If the
9.25 isnt on GEM you could allways get the refractor and mount for
around. The C-102 is around 399.00 with mount and if you dont need
the mount its even less.

Best of luck

Rich


On 18 Feb 2004 12:38:59 -0800, (Dave
Bohnsack) wrote:

Hello Group,

After reading through the archives and other sources about the
relationship between aperture, optical quality, scope design and
vulnerability to seeing conditions, I'm asking for opinions about my
next move.

I'm primarily into visual planetary, lunar and doubles work. I've got
a well-collimated C9.25 with at least good optics (based on star test
and images during fleeting moments of still air). I keep the scope in
an unheated garage, so it reaches thermal equilibrium fairly quickly.

Here's the problem: I live in southeast Wisconsin and the seeing is
usually poor. I'm at a relatively dark site, and I have my share of
clear cold nights, but 9 times out of 10, the atmosphere is just
boiling. (Why they decided to put the world's largest refractor in
the Yerkes Observatory at Williams Bay is beyond me.) The seeing
rarely supports magnification beyond about 200x (12mm ortho).

I've tried an off-axis mask to reduce the effective aperture (and to
eliminate the effects on contrast of a central obstruction), but the
image is dreadfully dim. I also realize that I'm losing resolving
power with the mask.

I'm thinking about going to a smaller scope to reduce the negative
effects of poor seeing. Given the generally deleterious effects of a
central obstruction, and further assuming that fewer optical surfaces
means fewer opportunities for error, I'm thinking of a refractor in
the 4 to 6-inch range. Because my work usually calls for high
magnification, I'm thinking a slow achromat (f/10, f/15, higher?)
might work for me. Perhaps an apochromat and a good barlow (though my
funds are limited). Portability is not an issue as I'm planning a
permanent installation eventually.

So, what would you do if you were me? I'm not expecting definitive
answers, but rather opinions/solutions for my particular situation.

Thanks in advance.

Dave