From: "DAVID K OESTREICH" 
To: "Vladimir Galogaza" ,
        "ATM shore" 
Reply-To: "DAVID K OESTREICH" 


I appreciate Vladimir's letter of "tough love". I mad the mistake
of following the canon according to Dobson implicitly. There are other ways
including the moldy texerau book which I have read. The problem to finding
a good book is which book. There are more bad books than there are good.
The opinions sent back indicate there are as many opinions too. There does
eem to be a common thread... The tile tool. But I have had people tell me
destroy the lap and use the tool as well as yourself who indicates that I
should keep it. None of us probably has the perfect answer or probably is
the one true authority including the venerable old Mr. Dobson.  The
following is a lesson that I too should follow...---> Forget the baggage
of emotion and personality and deal with just the facts. This whole
approach should be dealt with the same idealistic scientific impartiality
that many of these scientific disciplines require.
John was a pain in the ass on many account and anyone who has had any
dealings with him will verify this. There is his way and only his way. He
has had some success in his method of mirror grinding/polishing.
I don't wish to denigrate his acchievement. Many disciplines involve a
master and a learner. Sometime the combination of two are incompatible. The
old adage that eventually the student has gone beyond the master probable
is true. But it ONLY BECOMES TRUE WITH TIME. We all need to learn from
someone. Only through that learning process and future endeavors at
experimentation does one learn "the true way".
You may indeed have attained your mater's or journeymen status in this
endeavor. Other's have not other's rely on the opion of a master to give us
at least some initial guidance. Remember you were probably at my level at
one time.
You probably had the same issues in determining an appropriate method. The
fact that the initial attempt left a bad taste in my mouth was in no small
part due to the irracible nature of John Dobson. The fact that I want to
try again speaks volumes. Some of us quit easily. I don't think I am one of
them.
I made mistakes and the methods we used to test our optics were meager at
best. I made the mistake of following John's junkyard approach to scope
building. It didn't seem to work for me. That is why I am here asking these
questions.
Please Vlad do us all a favor and remember where you started before passing
judgement on others.
-Karlo
----- Original Message -----
From: "Vladimir Galogaza" 
To: "ATM shore" 
Sent: Friday, December 20, 2002 8:54 AM Subject: Re: ATM HELP! mirror
making crossroads


>
> David,
>
> If it is true that  mirror has so wide "edge" than you might consider
> that it was never really finished .
> You said that it takes you six months to regain your composure.
> It seems to me that   you are bound to
> another disappointment if you will not modify your approach.
>  This is my reaction to the sentence:"Last summer I took a telescope
making
> class
> from John Dodbson. A not entirely pleasurable experience. "
>
> If you do not understand what you are doing, no amount of authority
> can save you from yourself. You may read good books and may
> work with good people and falsely think that this suffice to protect you
> from mistakes.
>
> If you left  your instructor to measure focal length  FOR you ,
> or INSTEAD of you,  than even if he made mistake
> you made it also, and much more important one.
> You did not check on his measurements which you should, not in order to
> question his authority but to see if you understood what he learned you
> by duplicating (or not) his measurement.
>
> Richard Schwartz, "authority on antiauthority"   wrote a lot on this
> subject for our list. So the problem is not uncommon.
>
> Some are in need for advices from gurus to be led by hand comfortably but
> blindly,
>  and some to confirm their own conclusions. It is up to you to choose.
>
> From your letter I see that now you are inclined to follow the second path
> which is optimistic development and kind of warranty for success
> and satisfaction.
>
> >I will need to remove the pitch and begin grinding anew.
>
> Make new tile tool and regrind the mirror to sphere to the very edge
> before starting polishing.
> Save your polishing tool for later polishing of a reground mirror.
> It can be  modified ,  to the new  f/6 curve.
>
> >My suspicion is that the curve never made its way out there in
> >rough grinding.
>
> You should be able to see this immediately by simple Sharpie test, and
later
> at polishing by KE and Ronchi test. You did not mention testing.
> Have you done it and how?
> I will suggest, before doing anything at all  make a good KE and Ronchi
test
> of the present mirror and find out what kind of surface you have got.
>
> Measure the ROC while grinding, with spherometer, template, or other
method
> while keeping sphericity until you are at required f-number but do not
> insist on 6.000 because Richard will get you.
>
> From your present sagita of 2.5 mm you have to dig additional
>   0.8 mm for f/6 ( approximately). You may do that with finer than 80
grit.
> There is no law on this. Its compromise between spending time to remove
deep
> pits
> and  making smaller pits. I think there is no consensus about this.
>
> >I really don't think that fine grinding could have made such an impact on
> >the curve...particularly because I was sooooo careful in fine grinding of
> >not going over the edge of the mirror with the tool.
>
> Going over the edge with a tool is not uncarefulness, it is part of the
> usual procedure. Because you did not,  it may caused  this edge problem.
> Regarding possible impact of the fine grinding on the curve, it suffice to
> say that  figuring usually starts from polished sphere and is done  by
> POLISHING.
>  So grinding with any size grit can have considerable impact on curve.
>  Do not fool yourself. We are speaking in terms of wavelengths.
>
> >This is based on the tremendously sucky reading I got off the star test.
>
> How you did your collimation? Is your mirror coated?
>
> >. I took the advice of someone who either has diminished visual acuity or
> >diminished faculties.That is over ...............
>
> How can you tell that it is over? What makes you so sure about it?
>
> Starting with 12.5" mirror is not easy task. That you have made some
> mistakes could be expected, but you have made it to the complete scope
which
> is great
> achievement. Your decision to make it even better is also great. I wish
you
> all success in this.
> Have a happy New Year.
>
>
> Regards
> Vladimir.
>
>
>
>
>
>
>
>

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