Some how the address got changed
Subject: Re: Fw: War dogs--Dogs that are US NAVY SEALS -- fantastic photos
 
http://blogs.canoe.ca/parker/general/the-dog-that-cornered-osama-bin-laden/
this says page not found....

-
War dogs--Dogs that are US NAVY SEALS -- fantastic photos
>
>More on the war dogs and links to the original ones that many have seen.  All
wonderful!
>War dogs--Dogs that are US NAVY SEALS
>>
>>Now you will know the rest of the story:
>>>http://blogs.canoe.ca/parker/general/the-dog-that-cornered-osama-bin-laden/  

[Non-text portions of this message have been removed]

Well this forum has been very quiet so I may as well try to liven it up.
I live in the Southern hemisphere and have ordered a 40 inch F3 from a well
respected US optician. My first view of the heavens apart from a crappy Kmart
scope many many years ago was through a 32 inch F3.6 Kennedy mirror and I must
say I was blown away. I knew then that I was lucky enough to have the funds to
afford that kind of a scope or better so I thought, why not? Rather than a new
Landcruiser or some other bauble, why not get something that totally grounds me
every time I use it? Just as important, I thought this type of scope would
possibly connect me with other people who had similar views to myself in terms
of our place in the universe and where we in the West are currently heading. I
hope for your best wishes as I embark upon my journey. For those of you in North
America, Europe and Australia who have never seen the full glory of the Southern
Sky in a big scope, I hope to be able to share my good fortune with you in the
not too distant future.

I hope you have a very large guest room. :)

-ad

On Fri, Sep 2, 2011 at 10:25, Mike Paulus <mikepaulus79@...> wrote:

> **
>
>
> Well this forum has been very quiet so I may as well try to liven it up.
> I live in the Southern hemisphere and have ordered a 40 inch F3 from a well
> respected US optician. My first view of the heavens apart from a crappy
> Kmart scope many many years ago was through a 32 inch F3.6 Kennedy mirror
> and I must say I was blown away. I knew then that I was lucky enough to have
> the funds to afford that kind of a scope or better so I thought, why not?
> Rather than a new Landcruiser or some other bauble, why not get something
> that totally grounds me every time I use it? Just as important, I thought
> this type of scope would possibly connect me with other people who had
> similar views to myself in terms of our place in the universe and where we
> in the West are currently heading. I hope for your best wishes as I embark
> upon my journey. For those of you in North America, Europe and Australia who
> have never seen the full glory of the Southern Sky in a big scope, I hope to
> be able to share my good fortune with you in the not too distant future.
>
>
>



--
attilla danko, danko@..., http://cleardarksky.com/csk


[Non-text portions of this message have been removed]

Mike,
Who are you having make the primary and secondary mirrors? Who is going to make
the structure to carry these behemoth pieces of glass? Curious minds would like
to know<g>. BTW, congrats on stepping up to such large aperture. I can only
imagine how your Southern constellations are going to look in that beautiful
scope. We never have Omega Centauri more than about 10-15 degrees above the
horizon and you will be looking at it overhead with 40" of aperture! Bob

--- In bigdob@yahoogroups.com, "Mike Paulus" <mikepaulus79@...> wrote:
>
> Well this forum has been very quiet so I may as well try to liven it up.
> I live in the Southern hemisphere and have ordered a 40 inch F3 from a well
respected US optician. My first view of the heavens apart from a crappy Kmart
scope many many years ago was through a 32 inch F3.6 Kennedy mirror and I must
say I was blown away. I knew then that I was lucky enough to have the funds to
afford that kind of a scope or better so I thought, why not? Rather than a new
Landcruiser or some other bauble, why not get something that totally grounds me
every time I use it? Just as important, I thought this type of scope would
possibly connect me with other people who had similar views to myself in terms
of our place in the universe and where we in the West are currently heading. I
hope for your best wishes as I embark upon my journey. For those of you in North
America, Europe and Australia who have never seen the full glory of the Southern
Sky in a big scope, I hope to be able to share my good fortune with you in the
not too distant future.
>

Hi Mike,
I've been fortunate in having the use of a 24" at Magellan Observatory in
Australia for 8 nights (4 usable) a few years ago; in my opinion, the southern
skies are better than ours in terms of objects - we have nothing that can
compare to Eta Carinae or the Magellanics, for example. Before that, in 2000, I
took a 13.1" with me to South Island, New Zealand (45° south latitude) for a
couple of weeks. Having a 1-meter telescope there will be terrific!. Where are
you located? When do you expect delivery?
Clears,
Shneor

--- In bigdob@yahoogroups.com, "Mike Paulus" <mikepaulus79@...> wrote:
>
> Well this forum has been very quiet so I may as well try to liven it up.
> I live in the Southern hemisphere and have ordered a 40 inch F3 from a well
respected US optician. My first view of the heavens apart from a crappy Kmart
scope many many years ago was through a 32 inch F3.6 Kennedy mirror and I must
say I was blown away. I knew then that I was lucky enough to have the funds to
afford that kind of a scope or better so I thought, why not? Rather than a new
Landcruiser or some other bauble, why not get something that totally grounds me
every time I use it? Just as important, I thought this type of scope would
possibly connect me with other people who had similar views to myself in terms
of our place in the universe and where we in the West are currently heading. I
hope for your best wishes as I embark upon my journey. For those of you in North
America, Europe and Australia who have never seen the full glory of the Southern
Sky in a big scope, I hope to be able to share my good fortune with you in the
not too distant future.
>

Mike,
I noticed on a recent post by Mike Lockwood that he is currently working on a
1.1 meter mirror. That sounds surprisingly close to what you are getting<g>. If
in fact you are getting one of Lockwood's mirrors, you will be in for a treat. I
have a 28" f/3.54 Lockwood/Starmaster and really love how the scope/mirror
performs. Of course we only have steady Florida skies and cannot go lower that
18 degrees latitude down in the Keys. We get a little glimpse of what you have
overhead. The only thing is that the Moon is corretly positioned here and upside
down for you guys<g>. Bob

--- In bigdob@yahoogroups.com, "gumbydad2002" <wsrs@...> wrote:
>
> Mike,
> Who are you having make the primary and secondary mirrors? Who is going to
make the structure to carry these behemoth pieces of glass? Curious minds would
like to know<g>. BTW, congrats on stepping up to such large aperture. I can only
imagine how your Southern constellations are going to look in that beautiful
scope. We never have Omega Centauri more than about 10-15 degrees above the
horizon and you will be looking at it overhead with 40" of aperture! Bob
>
> --- In bigdob@yahoogroups.com, "Mike Paulus" <mikepaulus79@> wrote:
> >
> > Well this forum has been very quiet so I may as well try to liven it up.
> > I live in the Southern hemisphere and have ordered a 40 inch F3 from a well
respected US optician. My first view of the heavens apart from a crappy Kmart
scope many many years ago was through a 32 inch F3.6 Kennedy mirror and I must
say I was blown away. I knew then that I was lucky enough to have the funds to
afford that kind of a scope or better so I thought, why not? Rather than a new
Landcruiser or some other bauble, why not get something that totally grounds me
every time I use it? Just as important, I thought this type of scope would
possibly connect me with other people who had similar views to myself in terms
of our place in the universe and where we in the West are currently heading. I
hope for your best wishes as I embark upon my journey. For those of you in North
America, Europe and Australia who have never seen the full glory of the Southern
Sky in a big scope, I hope to be able to share my good fortune with you in the
not too distant future.
> >
>

----- Original Message -----

> From: gumbydad2002 <wsrs@...>
>
> Mike,
> I noticed on a recent post by Mike Lockwood that he is currently working on a
> 1.1 meter mirror. That sounds surprisingly close to what you are
> getting<g>.

But that might be the 1.1m cellular mirror first mentioned here a few years ago-
I'm pretty sure he's doing that one (after very long delays in finding someone
who could make the cellular blank).

OTOH, who else is known for making such large, fast mirrors?

-John


> If in fact you are getting one of Lockwood's mirrors, you
> will be in for a treat. I have a 28" f/3.54 Lockwood/Starmaster and really
> love how the scope/mirror performs. Of course we only have steady Florida
skies
> and cannot go lower that 18 degrees latitude down in the Keys. We get a little
> glimpse of what you have overhead. The only thing is that the Moon is corretly
> positioned here and upside down for you guys<g>. Bob
>
> --- In bigdob@yahoogroups.com, "gumbydad2002" <wsrs@...> wrote:
>>
>>  Mike,
>>  Who are you having make the primary and secondary mirrors? Who is going to
> make the structure to carry these behemoth pieces of glass? Curious minds
would
> like to know<g>. BTW, congrats on stepping up to such large aperture. I
> can only imagine how your Southern constellations are going to look in that
> beautiful scope. We never have Omega Centauri more than about 10-15 degrees
> above the horizon and you will be looking at it overhead with 40" of
> aperture! Bob
>>
>>  --- In bigdob@yahoogroups.com, "Mike Paulus"
> <mikepaulus79@> wrote:
>>  >
>>  > Well this forum has been very quiet so I may as well try to liven it
> up.
>>  > I live in the Southern hemisphere and have ordered a 40 inch F3 from a
> well respected US optician. My first view of the heavens apart from a crappy
> Kmart scope many many years ago was through a 32 inch F3.6 Kennedy mirror and
I
> must say I was blown away. I knew then that I was lucky enough to have the
funds
> to afford that kind of a scope or better so I thought, why not? Rather than a
> new Landcruiser or some other bauble, why not get something that totally
grounds
> me every time I use it? Just as important, I thought this type of scope would
> possibly connect me with other people who had similar views to myself in terms
> of our place in the universe and where we in the West are currently heading. I
> hope for your best wishes as I embark upon my journey. For those of you in
North
> America, Europe and Australia who have never seen the full glory of the
Southern
> Sky in a big scope, I hope to be able to share my good fortune with you in the
> not too distant future.
>>  >
>>
>
>
>
>
> ------------------------------------
>
> Yahoo! Groups Links
>
>
>

Hi,

--- In bigdob@yahoogroups.com, John Mahony <jmmahony@...> wrote:
> > From: gumbydad2002 <wsrs@...>
> > I noticed on a recent post by Mike Lockwood that he is currently
> > working on a
> > 1.1 meter mirror. That sounds surprisingly close to what you are
> > getting<g>.

> But that might be the 1.1m cellular mirror first mentioned here a
> few years ago- I'm pretty sure he's doing that one (after very
> long delays in finding someone who could make the cellular blank).

You're close - it's a 1.1m monolithic Supremax replacement for a cellular blank
that never showed up.  One vendor never delivered, and another declined to
produce it.

I am producing two 40" f/3s for clients (one amateur, one scientific), and one
for myself if I ever get time to finish it!  There are a number of other 40"+
mirrors in the queue too.

I recently completed a 50" f/2.2 R-C primary, and will be testing it in
combination with a secondary mirror soon, in order to verify the figure of the
secondary mirror.

> OTOH, who else is known for making such large, fast mirrors?

Some claim to.  Do your research and be careful who you give your money to.

Mike Lockwood

> OTOH, who else is known for making such large, fast mirrors?


Some claim to.  Do your research and be careful who you give your money to.


Steve Kennedy also makes excellent fast mirrors and have been making them longer
than anyone else.  I have not seen a bad Kennedy mirror and I have looked
through at least ten of them including recent examples.  I don't know what
happened with Wambo's mirror, but given how that process and review evolved, I
have serious doubts about the validity of the review.    Steve never had a
chance to look at the mirror so we will never know what happened.


Also for all of you to know, Kennedy is now using OMI as his coater as he had
some serious problems with Flabeg...Wambo's mirror included.


BTW, Kennedy will be making my next fast 28" mirror.


Clear skies,

Alvin






[Non-text portions of this message have been removed]

"Steve Kennedy also makes excellent fast mirrors and have been making them
longer than anyone else.  I have not seen a bad Kennedy mirror and I have looked
through at least ten of them including recent examples..."
Alvin

Respectfully, it's a good thing you never observed with my K32.  Your "have not
seen" record would have quickly come to an end.

Good Luck with your next Kennedy mirror.

dave

Hi Dave,


I know of two "bad" 32 inch mirrors. Do you have the other Webster 32?  Did you
talk with Kennedy to resolve the issue?  I know of two others had their mirrors
recoated at OMI and one of them got it back and the difference was night and
day.  The figure was fine, just the coating.  The other didn't get it back yet
as it is being coated now.  One is a 30" f/3.3 and other is 24" f/3.3.


I think your issue might be just the coating.  Talk with Kennedy if you haven't
yet.


Best,

Alvin

----------------------------------------

From: "daveleason" <davensldvd@...>

Sent: Wednesday, September 07, 2011 1:39 AM

To: bigdob@yahoogroups.com

Subject: [bigdob] Re: Large fast dob




"Steve Kennedy also makes excellent fast mirrors and have been making them
longer than anyone else.  I have not seen a bad Kennedy mirror and I have looked
through at least ten of them including recent examples..."

Alvin


Respectfully, it's a good thing you never observed with my K32.  Your "have not
seen" record would have quickly come to an end.


Good Luck with your next Kennedy mirror.


dave






[Non-text portions of this message have been removed]

--- In bigdob@yahoogroups.com, "parabola30" <parabola30@...> wrote:
> Some claim to.  Do your research and be careful who you give your
> money to.

Just for clarification, the discussion was about a 1.1m mirror, and I was
talking about ~1-meter and larger mirrors.

I was talking about doing your research so that you actually receive a mirror,
rather than getting nothing.  In that size range you need to be careful.

Mike Lockwood

Hi folks,

Well you guessed it. Mike Lockwood is making both the primary and secondary. I'm
the "amateur" mentioned in Mike L's response. The truth is that "newbie,
kinderstronomer" is probably more applicable to my astronomy knowledge and
skills but hey, I figure you're never too old too learn something new. Delivery
is scheduled around April next year and SDM telescopes based here in Australia
is making the scope which will have all the goto and tracking functions (argo,
servocat) to make finding things to observe relatively easy. The scope will be
located around 38S on a farm with relatively dark skies. I'm currently planning
the site of the scope and observatory (roll back roof) and maybe some attached
accomodation to allow for visitors. What's a reasonable amount someone would pay
to use a 40inch F3 in Southern skies with self contained accomodation per night
I wonder (not a lot of money in sheep unfortunately) which helps to pay for some
of the the scope/farm maintenance and my red wine supply?
Also important is the design of the access ramp/ladder. I'd like something that
is easy and comfortable to use for long observing sessions, maybe some kind of
self moving chair on hydraulic ramp.
A lot of things to get sorted before the scope arrives.
Cheers
Mike

--- In bigdob@yahoogroups.com, "Mike Paulus" <mikepaulus79@...> wrote:
>
> Well this forum has been very quiet so I may as well try to liven it up.
> I live in the Southern hemisphere and have ordered a 40 inch F3 from a well
respected US optician. My first view of the heavens apart from a crappy Kmart
scope many many years ago was through a 32 inch F3.6 Kennedy mirror and I must
say I was blown away. I knew then that I was lucky enough to have the funds to
afford that kind of a scope or better so I thought, why not? Rather than a new
Landcruiser or some other bauble, why not get something that totally grounds me
every time I use it? Just as important, I thought this type of scope would
possibly connect me with other people who had similar views to myself in terms
of our place in the universe and where we in the West are currently heading. I
hope for your best wishes as I embark upon my journey. For those of you in North
America, Europe and Australia who have never seen the full glory of the Southern
Sky in a big scope, I hope to be able to share my good fortune with you in the
not too distant future.
>

What is the market like for a coma corrector for very fast big dobs?   I am
starting to figure a super fast 32" and find that the Televue type 2 Parracorr
will introduce significant vignetting.  It is a verg good lens and I like the
way they have adapted it for both visual and photographic applications. 
However, if we could find a supplier who will make one in a 3" barrel, that
would be a significant improvement.  As others are now makeing the superfast
dobs, I can see a definite market.  What are your ideas?

Dr. Phill

>>>
What is the market like for a coma corrector for very fast big dobs?   I am
starting to figure a super fast 32" and find that the Televue type 2
Parracorr will introduce significant vignetting.


How 'super fast' is the 32"? Sounds wonderful!

I've been observing with my f/3.0 scope for a year and a half now, first
using the original TV coma corrector, then switching to the P2 when it came
out. What a nice improvement. Stars are truly pinpoint to the edge - clearly
better than a f/5 scope without a coma corrector. I'm into extreme fields so
it is important that there be no noticeable vignetting, whether from the
coma corrector, the diagonal or upper ring. I find no noticeable vignetting
when observing with my biggest exit pupil eyepiece (6mm in my scope), the
21mm Ethos.

In fact, it's opened up a new world of RFT viewing. I get more aperture for
the same field of view, which has meant that I can see large scale objects
better than ever before. The number one comment I get by far from other
amateurs is how bright the objects appear.

I've also got chances to observe with f/3.5 scopes fairly extensively (18
and 20 inches aperture) and can't see any vignetting here either.

I use a tight upper end - just a fraction of an inch larger than the mirror.
That reduces overall size and weight by ~15%. Also the upper end can now be
used as a baffle.

For more, see my f/3.0 scope at
http://www.bbastrodesigns.com/ZipDob/ZipDob.html Some observing comments are
near the end.

See Babcock's f/3.5 scope at http://www.bbastrodesigns.com/osp11/osptwa.html


Hmm, I don't seem to have images of Swayze's 18 inch f/3.5, which is a most
wonderful scope - the optics are incredible and the views stunning. It's a
conventional closed tube affair. He uses a bino-viewer to boot - I was
somewhat surprised to find no compromise in the views - we looked at a lot
of stuff with it.

See my RFT comments at http://www.bbastrodesigns.com/rft.html

See my upper ring sizing comments at
http://www.bbastrodesigns.com/SmallerUpperCage/SmallerUpperCage.html

See my comments on grinding my f/3.0 at
http://www.bbastrodesigns.com/JoyOfMirrorMaking/JoyOfMirrorMaking.html


Mel Bartels

My neighbor was over the other night and had a chance to see my 28" Newt
although we were using my 18" that night for a neighborhood show-and-tell with
some neighborhood children. The topic came around to how many large Newts 28"
and larger are in the USA? I said to him that I guessed maybe 300? Does anybody
have a sense of what a more accurate number might be? Bob

If I had to guess based just on my local region (Indiana), I'd come up with a
considerably lower estimate- maybe 100.  But there are obviously other parts of
the country with much better observing conditions, and others with higher
average incomes, so I don't really know.  How many are there just in Arizona?  S
California?

The number seems to increase considerably if you drop to 24"/25".  In the other
direction, about a decade ago I heard two vendors at a major star party trying
to list all the existing 36"+ amateur scopes they knew of in the US, and they
came up with about 6.  I think it's at least twice that now, especially if you
add a few in other countries.


-John



----- Original Message -----
> From: gumbydad2002 <wsrs@...>
>
> My neighbor was over the other night and had a chance to see my 28" Newt
> although we were using my 18" that night for a neighborhood show-and-tell
> with some neighborhood children. The topic came around to how many large Newts
> 28" and larger are in the USA? I said to him that I guessed maybe 300? Does
> anybody have a sense of what a more accurate number might be? Bob

I'd guess 100. The Oregon Star Party is a major center of large dob activity
over the years. I count maybe 12-15 *different* 28" and larger scopes (5
scopes of 40" and larger) over the years. Multiply that by a half dozen
centers across the USA and one gets ~100-ish.

There are many more 26, 25 and 24 inch scopes - say 3x to 4x times more.

I'm more interested in the most popular large dob size. It appears to be
16", based on the Oregon Star Party over the years. That makes sense because
the trade-off curve between expense and results/effectiveness/total usage
takes a nose dive beyond 16-20".

Mel Bartels




-----Original Message-----
From: bigdob@yahoogroups.com [mailto:bigdob@yahoogroups.com] On Behalf Of
John Mahony
Sent: Sunday, September 11, 2011 10:28 AM
To: bigdob@yahoogroups.com
Subject: Re: [bigdob] How Many Dobs 28" and larger in the USA

If I had to guess based just on my local region (Indiana), I'd come up with
a considerably lower estimate- maybe 100.  But there are obviously other
parts of the country with much better observing conditions, and others with
higher average incomes, so I don't really know.  How many are there just in
Arizona?  S California?

The number seems to increase considerably if you drop to 24"/25".  In the
other direction, about a decade ago I heard two vendors at a major star
party trying to list all the existing 36"+ amateur scopes they knew of in
the US, and they came up with about 6.  I think it's at least twice that
now, especially if you add a few in other countries.


-John



----- Original Message -----
> From: gumbydad2002 <wsrs@...>
>
> My neighbor was over the other night and had a chance to see my 28" Newt
> although we were using my 18" that night for a neighborhood show-and-tell
> with some neighborhood children. The topic came around to how many large
Newts
> 28" and larger are in the USA? I said to him that I guessed maybe 300?
Does
> anybody have a sense of what a more accurate number might be? Bob


------------------------------------

Yahoo! Groups Links

Mel's opinion and mine differ, both in terms of the weight difference with a
slightly larger UTA, and with the vignetting significance.
While the math works for calculating light loss at the edge of the field, it
depends on how you view the vignetting.  For one star at one edge of the field,
the math on his site works out.  But the vignetting occurs at every angle,
meaning the entire periphery of the field is dimmed, not just one side.

Second, the light loss caused by a small entrance pupil in the scope multiplies
the light loss from the secondary itself.  The reduced edge brightness is
compounded by the significant vignetting of the typical secondary size.

But, is this a vignetting that has its merits due to a significant weight loss
in the scope?

Not as I see it.

The mirror box, groundboard, and pole lengths can all remain the same if the UTA
is expanded in size slightly (though a baffle directly above the primary might
have to have its opening expanded a tiny amount).  In fact, the scope is more
rigid if the poles are not parallel in the first place, so having a scope whose
poles expand slightly to a larger diameter UTA is a good thing.

Plus, the heavier UTA will be only a small amount heavier.  I'd be very liberal
to say 1-1.5 lbs heavier on a 100 lb scope, allowing for a slight increase in
secondary size, spider vane lengths, and wooden ring diameter(s).

Now because very fast scopes are likely to use shorter focal length eyepieces as
a low power eyepiece (I'm seeing the 21 Ethos considered for many short dobs'
lowest power eyepiece), the field stop is smaller and the amount the UTA should
be larger than the primary mirror is reduced thereby.

But since you can achieve essentially zero vignetting with a UTA ID about the
same size as the primary mirror plus the field stop of the lowest power
eyepiece, if the f/3 scope is using a 21 Ethos, the scope's UTA's I.D. only has
to be 1.4" larger than the mirror to eliminate entrance pupil vignetting.  That
0.9" increase in diameter of the UTA won't add the 10-15 lbs that Mel mentions. 
Especially since no extra weight needs to be added to the mirror box to
counterbalance the heavier UTA if the altitude axis is slightly repositioned in
the plans for the scope.  Any extra height in the sideboards will also add very
little extra weight--maybe a pound.

When I rebuilt the UTA on my scope to a larger diameter, I simply used a few
construction tricks to keep the weight nearly the same, even though my UTA
increased in diameter by nearly an inch.  In my case, I did not even have to add
additional weight to the mirror box, nor increase the height of the side boards
to change the altitude axis position.

Since the weight difference is negligible, there doesn't appear to be a good
reason to reduce the size of the UTA and vignette the edge of the field.

I could be missing something here, but I don't think there is any value in
reducing the UTA I.D. to such a small size.

Where significant weight saving can occur is in the weight of the primary
mirror.  I'm moving from a 55mm thick mirror to a 32mm thick mirror, and that
will save weight in any design.

Don Pensack
Los Angeles



--- In bigdob@yahoogroups.com, "Mel Bartels" <mbartels@...> wrote:
>
> >>>
> What is the market like for a coma corrector for very fast big dobs?   I am
> starting to figure a super fast 32" and find that the Televue type 2
> Parracorr will introduce significant vignetting.
>
>
> How 'super fast' is the 32"? Sounds wonderful!
>
> I've been observing with my f/3.0 scope for a year and a half now, first
> using the original TV coma corrector, then switching to the P2 when it came
> out. What a nice improvement. Stars are truly pinpoint to the edge - clearly
> better than a f/5 scope without a coma corrector. I'm into extreme fields so
> it is important that there be no noticeable vignetting, whether from the
> coma corrector, the diagonal or upper ring. I find no noticeable vignetting
> when observing with my biggest exit pupil eyepiece (6mm in my scope), the
> 21mm Ethos.
>
> In fact, it's opened up a new world of RFT viewing. I get more aperture for
> the same field of view, which has meant that I can see large scale objects
> better than ever before. The number one comment I get by far from other
> amateurs is how bright the objects appear.
>
> I've also got chances to observe with f/3.5 scopes fairly extensively (18
> and 20 inches aperture) and can't see any vignetting here either.
>
> I use a tight upper end - just a fraction of an inch larger than the mirror.
> That reduces overall size and weight by ~15%. Also the upper end can now be
> used as a baffle.
>
> For more, see my f/3.0 scope at
> http://www.bbastrodesigns.com/ZipDob/ZipDob.html Some observing comments are
> near the end.
>
> See Babcock's f/3.5 scope at http://www.bbastrodesigns.com/osp11/osptwa.html
>
>
> Hmm, I don't seem to have images of Swayze's 18 inch f/3.5, which is a most
> wonderful scope - the optics are incredible and the views stunning. It's a
> conventional closed tube affair. He uses a bino-viewer to boot - I was
> somewhat surprised to find no compromise in the views - we looked at a lot
> of stuff with it.
>
> See my RFT comments at http://www.bbastrodesigns.com/rft.html
>
> See my upper ring sizing comments at
> http://www.bbastrodesigns.com/SmallerUpperCage/SmallerUpperCage.html
>
> See my comments on grinding my f/3.0 at
> http://www.bbastrodesigns.com/JoyOfMirrorMaking/JoyOfMirrorMaking.html
>
>
> Mel Bartels
>

I counted 10 30 and larger at Okie Tex last year.  Three were larger than 30. 
The largest being 33 I think.  Almost no one from the west coast was there so
there is little overlap.

Dale Eason

Dale,

I have had two educated guesses. What is your guess as to how many 28" and over
dobs are in the USA?

Bob

--- In bigdob@yahoogroups.com, "atmpob" <atmpob@...> wrote:
>
>
> I counted 10 30 and larger at Okie Tex last year.  Three were larger than 30. 
The largest being 33 I think.  Almost no one from the west coast was there so
there is little overlap.
>
> Dale Eason
>

Hi, I'm writing from the U.K. where large Dobs are really thin on the ground,
and astro-imaging with small instuments seems to be the main aim of many,
although I wonder if the two are linked, as visual observation of galaxies and
also many other objects can only offer a feast for the eyes with a large
aperture, its a pity that most astronomical society do not give the chance for
people to look through a big dob,
   John Dobsons 24 inch (f6.5) inspired many of those who looked through it, and
despite its huge solid tube travelled around and was used by a great number of
people, but it was a group effort, more recent larger but "lighter" weight
instruments might be more common if more astronomers got together to help with
transport to great observing sites, if the trend is now to more moderate
apertures does that mean more lone observing than there was at the peak of the
dobsonian expansion?

Neil


--- In bigdob@yahoogroups.com, "Mel Bartels" <mbartels@...> wrote:
>
> I'd guess 100. The Oregon Star Party is a major center of large dob activity
> over the years. I count maybe 12-15 *different* 28" and larger scopes (5
> scopes of 40" and larger) over the years. Multiply that by a half dozen
> centers across the USA and one gets ~100-ish.
>
> There are many more 26, 25 and 24 inch scopes - say 3x to 4x times more.
>
> I'm more interested in the most popular large dob size. It appears to be
> 16", based on the Oregon Star Party over the years. That makes sense because
> the trade-off curve between expense and results/effectiveness/total usage
> takes a nose dive beyond 16-20".
>
> Mel Bartels
>
>
>
>
> -----Original Message-----
> From: bigdob@yahoogroups.com [mailto:bigdob@yahoogroups.com] On Behalf Of
> John Mahony
> Sent: Sunday, September 11, 2011 10:28 AM
> To: bigdob@yahoogroups.com
> Subject: Re: [bigdob] How Many Dobs 28" and larger in the USA
>
> If I had to guess based just on my local region (Indiana), I'd come up with
> a considerably lower estimate- maybe 100.  But there are obviously other
> parts of the country with much better observing conditions, and others with
> higher average incomes, so I don't really know.  How many are there just in
> Arizona?  S California?
>
> The number seems to increase considerably if you drop to 24"/25".  In the
> other direction, about a decade ago I heard two vendors at a major star
> party trying to list all the existing 36"+ amateur scopes they knew of in
> the US, and they came up with about 6.  I think it's at least twice that
> now, especially if you add a few in other countries.
>
>
> -John
>
>
>
> ----- Original Message -----
> > From: gumbydad2002 <wsrs@...>
> >
> > My neighbor was over the other night and had a chance to see my 28" Newt
> > although we were using my 18" that night for a neighborhood show-and-tell
> > with some neighborhood children. The topic came around to how many large
> Newts
> > 28" and larger are in the USA? I said to him that I guessed maybe 300?
> Does
> > anybody have a sense of what a more accurate number might be? Bob
>
>
> ------------------------------------
>
> Yahoo! Groups Links
>

Don, I always enjoy debating telescope design with you. Keep in mind though
that I spent a half year designing the scope and a year and a half using it
so I am very tuned into what happens at F3.

One does not have to take advantage of the slighter smaller size and lighter
weight that very fast f/3 telescopes offer. It's an individual choice - no
harm is done to the design.

Your comments that entire periphery of the field is dimmed and that typical
secondary sizes significantly vignette are not valid for optimized systems.

Further, expanding the upper end while leaving the mirror box the same size
is not ideal. That means that the upper end cannot fit into the mirror box
which wastes space. And the truss tubes are no longer parallel to the mirror
box, complicating design and building.

Finally, the formula that adds the field stop to the mirror diameter to
arrive at the upper end inner diameter ignores the diagonal's clipping of
the light cone and results in larger than necessary upper ends.

Usability of portable scopes is the combination of weight, size, time of
setup and ease of setup. Making the scope a little smaller and a little
lighter is important to me.  That's me; others will have other usability
requirements.

The illumination drop off at f/3 is extremely gradual. So much so that the
minimum sized diagonal is entirely adequate for visual use. The smallest
possible diagonal also allows a bit more light throughout the field. There
is an unnoticeable gain of light of a couple hundredths of magnitude at the
center of the field of view and an unnoticeable loss of light at the extreme
edge of the field of view of a tenth of a magnitude.

The impact of clipping the light cone at the diagonal's edge for the center
of the field means that the upper ring need be no larger than the mirror
diameter. I like to add a small design factor.

The result when viewing from the edge of the field of view is a tiny arc of
vignetted light, perhaps a couple hundreds of magnitude loss (compensated
for by the increased light throughput by virtue of the smaller optimized
diagonal). I explain all this on
http://www.bbastrodesigns.com/SmallerUpperCage/SmallerUpperCage.html which
includes actual images from my f/3 scope.

Mel Bartels



-----Original Message-----
From: bigdob@yahoogroups.com [mailto:bigdob@yahoogroups.com] On Behalf Of
pensack1
Sent: Monday, September 12, 2011 9:40 AM
To: bigdob@yahoogroups.com
Subject: [bigdob] Re: coma corrector for very fast dobs

Mel's opinion and mine differ, both in terms of the weight difference with a
slightly larger UTA, and with the vignetting significance.
While the math works for calculating light loss at the edge of the field, it
depends on how you view the vignetting.  For one star at one edge of the
field, the math on his site works out.  But the vignetting occurs at every
angle, meaning the entire periphery of the field is dimmed, not just one
side.

Second, the light loss caused by a small entrance pupil in the scope
multiplies the light loss from the secondary itself.  The reduced edge
brightness is compounded by the significant vignetting of the typical
secondary size.

But, is this a vignetting that has its merits due to a significant weight
loss in the scope?

Not as I see it.

The mirror box, groundboard, and pole lengths can all remain the same if the
UTA is expanded in size slightly (though a baffle directly above the primary
might have to have its opening expanded a tiny amount).  In fact, the scope
is more rigid if the poles are not parallel in the first place, so having a
scope whose poles expand slightly to a larger diameter UTA is a good thing.

Plus, the heavier UTA will be only a small amount heavier.  I'd be very
liberal to say 1-1.5 lbs heavier on a 100 lb scope, allowing for a slight
increase in secondary size, spider vane lengths, and wooden ring
diameter(s).

Now because very fast scopes are likely to use shorter focal length
eyepieces as a low power eyepiece (I'm seeing the 21 Ethos considered for
many short dobs' lowest power eyepiece), the field stop is smaller and the
amount the UTA should be larger than the primary mirror is reduced thereby.

But since you can achieve essentially zero vignetting with a UTA ID about
the same size as the primary mirror plus the field stop of the lowest power
eyepiece, if the f/3 scope is using a 21 Ethos, the scope's UTA's I.D. only
has to be 1.4" larger than the mirror to eliminate entrance pupil
vignetting.  That 0.9" increase in diameter of the UTA won't add the 10-15
lbs that Mel mentions.  Especially since no extra weight needs to be added
to the mirror box to counterbalance the heavier UTA if the altitude axis is
slightly repositioned in the plans for the scope.  Any extra height in the
sideboards will also add very little extra weight--maybe a pound.

When I rebuilt the UTA on my scope to a larger diameter, I simply used a few
construction tricks to keep the weight nearly the same, even though my UTA
increased in diameter by nearly an inch.  In my case, I did not even have to
add additional weight to the mirror box, nor increase the height of the side
boards to change the altitude axis position.

Since the weight difference is negligible, there doesn't appear to be a good
reason to reduce the size of the UTA and vignette the edge of the field.

I could be missing something here, but I don't think there is any value in
reducing the UTA I.D. to such a small size.

Where significant weight saving can occur is in the weight of the primary
mirror.  I'm moving from a 55mm thick mirror to a 32mm thick mirror, and
that will save weight in any design.

Don Pensack
Los Angeles



--- In bigdob@yahoogroups.com, "Mel Bartels" <mbartels@...> wrote:
>
> >>>
> What is the market like for a coma corrector for very fast big dobs?   I
am
> starting to figure a super fast 32" and find that the Televue type 2
> Parracorr will introduce significant vignetting.
>
>
> How 'super fast' is the 32"? Sounds wonderful!
>
> I've been observing with my f/3.0 scope for a year and a half now, first
> using the original TV coma corrector, then switching to the P2 when it
came
> out. What a nice improvement. Stars are truly pinpoint to the edge -
clearly
> better than a f/5 scope without a coma corrector. I'm into extreme fields
so
> it is important that there be no noticeable vignetting, whether from the
> coma corrector, the diagonal or upper ring. I find no noticeable
vignetting
> when observing with my biggest exit pupil eyepiece (6mm in my scope), the
> 21mm Ethos.
>
> In fact, it's opened up a new world of RFT viewing. I get more aperture
for
> the same field of view, which has meant that I can see large scale objects
> better than ever before. The number one comment I get by far from other
> amateurs is how bright the objects appear.
>
> I've also got chances to observe with f/3.5 scopes fairly extensively (18
> and 20 inches aperture) and can't see any vignetting here either.
>
> I use a tight upper end - just a fraction of an inch larger than the
mirror.
> That reduces overall size and weight by ~15%. Also the upper end can now
be
> used as a baffle.
>
> For more, see my f/3.0 scope at
> http://www.bbastrodesigns.com/ZipDob/ZipDob.html Some observing comments
are
> near the end.
>
> See Babcock's f/3.5 scope at
http://www.bbastrodesigns.com/osp11/osptwa.html
>
>
> Hmm, I don't seem to have images of Swayze's 18 inch f/3.5, which is a
most
> wonderful scope - the optics are incredible and the views stunning. It's a
> conventional closed tube affair. He uses a bino-viewer to boot - I was
> somewhat surprised to find no compromise in the views - we looked at a lot
> of stuff with it.
>
> See my RFT comments at http://www.bbastrodesigns.com/rft.html
>
> See my upper ring sizing comments at
> http://www.bbastrodesigns.com/SmallerUpperCage/SmallerUpperCage.html
>
> See my comments on grinding my f/3.0 at
> http://www.bbastrodesigns.com/JoyOfMirrorMaking/JoyOfMirrorMaking.html
>
>
> Mel Bartels
>




------------------------------------

Yahoo! Groups Links

Just in Sierra Vista, Az I know of 4 X 30" and larger with a 40" under
construction by someone. population 50k.  Neal

[Non-text portions of this message have been removed]

At Chiefland (Florida) Astronomy Village alone there are 36" and 42" Dobs.
Plus at least one frequent weekend visitor often brings his 30".

Mike

--- In bigdob@yahoogroups.com, "Neal Galt" <neal@...> wrote:
>
> Just in Sierra Vista, Az I know of 4 X 30" and larger with a 40" under
construction by someone. population 50k.  Neal
>
> [Non-text portions of this message have been removed]
>

Oooops...hit the 'send' button too soon.
Wanted to add that my 28" is there every new moon weekend and it is often joined
by at least one other 28.

Mike

--- In bigdob@yahoogroups.com, "mharveyww1" <mharveyww1@...> wrote:
>
> At Chiefland (Florida) Astronomy Village alone there are 36" and 42" Dobs.
> Plus at least one frequent weekend visitor often brings his 30".
>
> Mike
>
> --- In bigdob@yahoogroups.com, "Neal Galt" <neal@> wrote:
> >
> > Just in Sierra Vista, Az I know of 4 X 30" and larger with a 40" under
construction by someone. population 50k.  Neal
> >
> > [Non-text portions of this message have been removed]
> >
>

I live in San Diego and the astronomy club I belong
to has over 500 members. My friend has a 24" and I only
know of one other person with a 25". That is it, there
isn'n anything bigger.

    Best, John



--- In bigdob@yahoogroups.com, "Michael" <mharveyww1@...> wrote:
>
> Oooops...hit the 'send' button too soon.
> Wanted to add that my 28" is there every new moon weekend and it is often
joined by at least one other 28.
>
> Mike
>
> --- In bigdob@yahoogroups.com, "mharveyww1" <mharveyww1@> wrote:
> >
> > At Chiefland (Florida) Astronomy Village alone there are 36" and 42" Dobs.
> > Plus at least one frequent weekend visitor often brings his 30".
> >
> > Mike
> >
> > --- In bigdob@yahoogroups.com, "Neal Galt" <neal@> wrote:
> > >
> > > Just in Sierra Vista, Az I know of 4 X 30" and larger with a 40" under
construction by someone. population 50k.  Neal
> > >
> > > [Non-text portions of this message have been removed]
> > >
> >
>

John,

A friend of mine surmised that there may be less than 100 in the USA when you
use the criteria of >28". He thought the number might well be about 80? We all
know that there are a lot of 25/24 inch dobs running around the country. It
seems that above the 25" range, the scope count may diminish significantly?
Since this is the Big Dob site, I thought the question would be an interesting
one as I had commented about my neighbor's friends observation that this size
was fairly rare and had originally made a guess of about 300 which seems to
probably be a high number. Bob

--- In bigdob@yahoogroups.com, "john" <2kuhl@...> wrote:
>
>
>    I live in San Diego and the astronomy club I belong
> to has over 500 members. My friend has a 24" and I only
> know of one other person with a 25". That is it, there
> isn'n anything bigger.
>
>    Best, John
>
>
>
> --- In bigdob@yahoogroups.com, "Michael" <mharveyww1@> wrote:
> >
> > Oooops...hit the 'send' button too soon.
> > Wanted to add that my 28" is there every new moon weekend and it is often
joined by at least one other 28.
> >
> > Mike
> >
> > --- In bigdob@yahoogroups.com, "mharveyww1" <mharveyww1@> wrote:
> > >
> > > At Chiefland (Florida) Astronomy Village alone there are 36" and 42" Dobs.
> > > Plus at least one frequent weekend visitor often brings his 30".
> > >
> > > Mike
> > >
> > > --- In bigdob@yahoogroups.com, "Neal Galt" <neal@> wrote:
> > > >
> > > > Just in Sierra Vista, Az I know of 4 X 30" and larger with a 40" under
construction by someone. population 50k.  Neal
> > > >
> > > > [Non-text portions of this message have been removed]
> > > >
> > >
> >
>

I have SW  Dobsonian 8" like that one
http://www.canadiantelescopes.com/Shop-By-Brand/Dobsonians_3/Sky-Watcher-Traditi\
onal-8-Dobsonian
It is a good guy but I would like to peplace the scop from dob mount to
motorized EQ or Go To type mount. My question is:
is it enough to get QE5 or it should be QE6 only? Any suggestions would be
appreciated.
Thank you.

Alex
Toronto, Canada.

[Non-text portions of this message have been removed]

Go BIG or go home is my matto. Aperture rules.
 
George
 
From: Alex <va3ttt@...>
To: "bigdob@yahoogroups.com" <bigdob@yahoogroups.com>
Sent: Tuesday, September 13, 2011 12:02 PM
Subject: [bigdob] Want to replace Sky Watcher Dobsonian 8"

I have SW  Dobsonian 8" like that one
http://www.canadiantelescopes.com/Shop-By-Brand/Dobsonians_3/Sky-Watcher-Traditi\
onal-8-Dobsonian
It is a good guy but I would like to peplace the scop from dob mount to
motorized EQ or Go To type mount. My question is:
is it enough to get QE5 or it should be QE6 only? Any suggestions would be
appreciated.
Thank you.

Alex
Toronto, Canada.

[Non-text portions of this message have been removed]



------------------------------------

Yahoo! Groups Links



[Non-text portions of this message have been removed]