[ATM] Book Review.... sort of

["Jerry" <wa4guu@verizon.net>]

I don't even remember ordering this book.  Several weeks ago I found it on
the shelf among my telescope and ATM books. I guess the last time I ordered
some rouge and cerebral oxide from Willmann-Bell I must have decided another
book on the shelf would help prevent the others from falling over. It is the
newer ATM book "A Manual for Amateur Telescope Makers" by Karine and
Jean-Marc Lecleire and of course published By Willmann-Bell.

I am mainly interested in mirror making. Since grinding and polishing is
largely a simple process that once you have made one surface successfully,
you probably understand it well enough that there is not much motive for
spending money to read about it.  It is figuring that I would be interested
in.  I have no problem pushing a parabola onto a mirror. It took a while to
get the hang of it but it is easy now. Still, I am always interested in how
other people do it, and I haven't made a perfect edge yet.  Next time.

I used the 3 volume ATM books and Jean Texereau's "How to Make a Telescope"
all also published by Willmann Bell as my guide and had no knowledge or
experienced people helping me. That leaves a lot of room to learn something
I suppose.

The 3 volume ATM book while having much good information in them, also has
much misinformation. I would say that they were largely an impediment to
finishing my first mirror. For some reason it seems that bad information is
the easiest for a beginner to accept as correct. The books are a collection
of articles on various aspects of optics fabrication and a host of other
subjects related to ATM.  Good reading but don't try to make a mirror with
them as your only guide.

"How to Make a Telescope" however is very good. I can only find fault with
his method of making a pitch lap. That is so trivial that I shouldn't call
it a fault.  The method I use is not the easiest but I like it anyway, so I
will allow that peculiarity to Jean Texereau. His reduction of Foucault test
readings to an error profile is still a very good way to learn about
measuring a mirror. Many computer programs that serve this purpose have done
nothing but reproduce his method on a computer screen. Beginners could still
learn from doing it that way before they use the programs.  Texereau also
has some rather simple methods of determining a profile adequate for
figuring purposes right to the finished mirror that can be done quicker than
you can enter the data in the programs. All of his figuring methods are
illustrated on two pages. I've used all of them at one time or another.  My
only complaint is that I would have liked him to have described them more
fully. Still I have not found better anywhere. If you have, let me know.

Having used only those books, and for practical purposes really only one
book (methods that worked), Jean Texereau's "How to Make a Telescope", I
can't help but wonder if there are methods of equal value that he did not
cover.  I am always interested in how people figure their mirrors. 

There is more than one way of skinning a cat.  But when we talk about
figuring, there may be more than one way to do it right, there are even more
ways that are wrong and won't do it at all.


	This brings me to the new book "A Manual for Amateur Telescope
Makers".  I don't like to be negative, so I will ask a question or two.  Has
anyone used the figuring techniques in this book to successfully figure a
mirror?  If you did, did you find any of those methods to be wrong?  Of
course you can tell I have a negative view of some of the figuring
techniques I see in there. I use some of those techniques but not for what
they do. And since I have used them for other reasons, I think I have a
grasp of what they would do.  I don't think they will do what the book says
they do.

I have never seen any defect that required a figure 8 stroke to fix. With
ease, I have used straight strokes to fix anything. In one place working for
a half hour on a raised zone is recommended with no concern shown for the
magnitude of the defect. And I see where pressure is put on the wrong side
of the lap. I know that with a raised edge you have a choice of wearing the
high edge to the longer radius inside of it, or wearing what is inside it to
the shorter radius of the raised edge. The method described in the book
would have to be directed more specifically than stated.

I will be sure to try these methods as presented in the book on my next
mirror to see if I can force them to work as described.  Until I see them
actually work, from my experience I would have to say this is a serious step
backward from Jean Texereau's book.

I make no claim of being an expert. My opinion is based on my experience,
more than some and less than others. I am interested what other mirror
makers think of the figuring methods in these books.

My opinion is that Texereau is still the best guide to mirror making.

Jerry

	
 
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