To: "Russell Jocoy"
,milnecd{at}yahoo.com,atm{at}shore.net
From: Chuck Dethloff 
Reply-To: Chuck Dethloff 


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>>From: Clive Milne 
>>***snip***If your scope
>>still vibrates, I'd wager it's not the truss tubes at fault.
>>It might be time to take a good hard analytical look at the whole
>>design from the ground up.  Just because everyone has built them
>>basically the same way for for the last 15 years doesn't make it right.
>>It's high time we moved on.
>>    ~Clive.

At 11:00 PM 7/23/2003 -0400, Russell Jocoy wrote:

>           Here, here.... I agree, How can you blame vibration on supports
> when you are using
>primative secondary cages made of wood and rocker boxes of thick Plywood.


Guys,

I admit that I am troubled by parts of the above quotes. You know, maybe it
is time that we quit worrying so much about how others build scopes
compared to what "we" think is the best way. What has been done
in the past has worked very well for a lot of people. So have some of the
newer designs for others. There ain't one single right or wrong way to
design a scope, it comes down to pluses and minuses for _any_ design and
what goals are most important to the individual building the scope. I don't
see a "holy grail" of Dobsonian design out there, so lets not
pretend that there is one.

And what is adequate structurally comes down to a lot more than calculated
minimum values in the real world. Engineers have over-designed for many
years for one very good reason. So that the dang thing does not fall apart
if the materials weaken with age and cumulative stress, or perhaps they
 made an errant assumption or calculation somewhere along the way.
Like was obviously made recently by NASA engineers despite their qualifications.

Or maybe it is exposed to abnormal abuse on occasion. As an example, a
couple years ago a good friend of mine had his 20" Obsession tarped up
outside at my house to protect it from rain between observing sessions. The
next day unusually strong winds caught his OTA just right (well actually,
just wrong) and blew the OTA up and over out of the rocker box. It landed
upside down on its back apparently with the cage hitting the ground first.
Despite that it only sustained minimal mostly cosmetic damage. That
happened to be one of those primitive wooden cages Russell. If I was
wagering, I would bet that a more minimal cage ring and truss assembly
would have been crushed like an eggshell. Which by the way is also very
rigid for its mass.

I have looked through a lot of scopes over the years. Many of my friends
have built ultra-light scopes. I certainly do not want to offend them or
anyone else who likes a more minimal scope while making my points. But I
need to say what I honestly feel as well, and my opinions are not based
merely upon mistaken bias. Nor do I feel they are invalid because I don't
offer up pages of scientific data in support of my viewpoint. Those that
only accept that type of evidence are only seeing part of the big picture
IMHO. My thoughts are rather based upon my experiences and what I see
through the eyepiece of various other scopes.

Most of my frustrations here are with the insinuations from Clive and
others on this list from time to time that these old dinosaurs have just
outlived there useful time. Really? Granted, any scope of any design needs
to be well constructed not just well engineered to work at its best. But
regarding strength and rigidity (interpreted from at the eyepiece
performance), nothing I have seen exceeds the more traditional works of the
past 20 years if well constructed. And the vast majority of the more
minimal scopes I have seen are a lot more sensitive to vibration than the
traditional designs.

Having said that, I am now getting closer to 50 years old and weights that
I handled easily 20 years ago are more imposing. I can see why many folks
want lighter and more portable scopes. As a result of this, I am going to
build my new 24" in a much lighter fashion than I ever thought I would
ten years ago. And I readily admit that I never would have felt comfortable
even considering building a scope so minimal if not exposed to the work of
Mel Bartels, Greg Babcock, Bruce Sayre, Tom Osypowski, and others as well.
I am also inspired by the work of many of you that I have never met in
person. As I have worked through the design of this scope I think I visited
just about every web page out there put up about ultra light scopes. My
thoughts and design have been influenced not only by scopes I have looked
through, but also by the work of Stathis Kafalis, Ruediger Heins and others
that I will probably never have a chance to look through. I feel a measure
of appreciation and respect to all that have pushed the envelope over the
years and taught us new ways, including you Clive.

But please don't ignore or devaluate the positives of the past in an
attempt to enhance the glory of the present. Build what you like and let
others build what they like without making them feel ignorant or wasteful
for not building them in the latest fashion.

Chuck Dethloff


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From:
Clive Milne <milnecd{at}yahoo.com>
***snip***If your scope
still vibrates, I'd wager it's not the truss tubes at fault. It
might be time to take a good hard analytical look at the whole
design from the ground up.  Just because everyone has built
them
basically the same way for for the last 15 years doesn't make it right.
It's high time we moved on.
   ~Clive.
At 11:00 PM 7/23/2003 -0400, Russell Jocoy wrote:
     &nbs=
p;   
Here, here.... I agree, How can you blame vibration on supports when you
are using
primative secondary cages made of wood and rocker boxes of thick
Plywood.
Guys,
I admit that I am troubled by parts of the above quotes. You know, maybe it
is time that we quit worrying so much about how others build scopes
compared to what "we" think is the best way. What has
been done in the past has worked very well for a lot of people. So have
some of the newer designs for others. There ain't one single right or wrong
way to design a scope, it comes down to pluses and minuses for _any_ design
and what goals are most important to the individual building the scope. I
don't see a "holy grail" of Dobsonian design out there,
so lets not pretend that there is one.  And what is
adequate structurally comes down to a lot more than calculated minimum
values in the real world. Engineers have over-designed for many years for
one very good reason. So that the dang thing does not fall apart if the
materials weaken with age and cumulative stress, or perhaps they
<gasp> made an errant assumption or calculation somewhere
along the way. Like was obviously made recently by NASA engineers despite
their qualifications. Or maybe it is exposed to
abnormal abuse on occasion. As an example, a couple years ago a good friend
of mine had his 20" Obsession tarped up outside at my house to
protect it from rain between observing sessions. The next day unusually
strong winds caught his OTA just right (well actually, just wrong) and blew
the OTA up and over out of the rocker box. It landed upside down on its
back apparently with the cage hitting the ground first. Despite that it
only sustained minimal mostly cosmetic damage. That happened to be one of
those primitive wooden cages Russell. If I was wagering, I would bet that a
more minimal cage ring and truss assembly would have been crushed like an
eggshell. Which by the way is also very rigid for its mass.
 I have looked through a lot of scopes over the years.
Many of my friends have built ultra-light scopes. I certainly do not want
to offend them or anyone else who likes a more minimal scope while making
my points. But I need to say what I honestly feel as well, and my opinions
are not based merely upon mistaken bias. Nor do I feel they are invalid
because I don't offer up pages of scientific data in support of my
viewpoint. Those that only accept that type of evidence are only seeing
part of the big picture IMHO. My thoughts are rather based upon my
experiences and what I see through the eyepiece of various other scopes.
 Most of my frustrations here are with the insinuations
from Clive and others on this list from time to time that these old
dinosaurs have just outlived there useful time. Really? Granted, any scope
of any design needs to be well constructed not just well engineered to work
at its best. But regarding strength and rigidity (interpreted from at the
eyepiece performance), nothing I have seen exceeds the more traditional
works of the past 20 years if well constructed. And the vast majority of
the more minimal scopes I have seen are a lot more sensitive to vibration
than the traditional designs.  Having said that, I am
now getting closer to 50 years old and weights that I handled easily 20
years ago are more imposing. I can see why many folks want lighter and more
portable scopes. As a result of this, I am going to build my new
24" in a much lighter fashion than I ever thought I would ten
years ago. And I readily admit that I never would have felt comfortable
even considering building a scope so minimal if not exposed to the work of
Mel Bartels, Greg Babcock, Bruce Sayre, Tom Osypowski, and others as well.
I am also inspired by the work of many of you that I have never met in
person. As I have worked through the design of this scope I think I visited
just about every web page out there put up about ultra light scopes. My
thoughts and design have been influenced not only by scopes I have looked
through, but also by the work of Stathis Kafalis, Ruediger Heins and others
that I will probably never have a chance to look through. I feel a measure
of appreciation and respect to all that have pushed the envelope over the
years and taught us new ways, including you Clive. 
But please don't ignore or devaluate the positives of the past in an
attempt to enhance the glory of the present. Build what you like and let
others build what they like without making them feel ignorant or wasteful
for not building them in the latest fashion.  
Chuck Dethloff 



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