Re: ATM How thin is too thin?

[mike coslo <mjc5@psu.edu>]

macaddicted wrote:

> Actually cost is more of a consideration than weight. I am planning to build
> as much of the system as I possibly can. I would dearly like to start this
> project with grinding my own mirror. You were right when you said this is my
> first project. I have been looking around on the web at the costs and it
> seems that the cost of grinding and coating a primary is pretty close to the
> cost of a well ground and coated pre-made primary. I know there is still a
> savings, but comparing Newport's and Coulter's costs I have to wonder if it
> is worth the frustration for a scope that is smaller than my "dream" scope
> (comparing a  12.5" kit to a 13.1" primary/secondary). <snip>


	Hey, Dave. for keeping costs down, don't be afraid to prowl around.
What finally got me pushing glass was getting three 12.5 inch pyrex
blanks for 15 dollars each! The old gent who had them was moving away,
and was tired of moving the blanks with him. I also got a bunch of
optical glass and other goodies with. So if you are willing to search
and be patient, the deals are out there.

	Another cost related item will be what it will take to build a mirror
cell for the thin mirror. Lots of tradeoffs here

	<unsnip>
> system for a f/5-5.5 system for the larger system, if I do build it. Once I
> have learned how to complete a smaller system I would have more confidence
> in a building a larger one. <snip>

	This is a very good move.

> I am still in the process of building a foundation of information. I have
> been in contact with Richard, and I am going to discuss slumping with him. I
> have ordered the Kriege and Texereau books from William Bell <snip>

	I also took a look at slumping mirrors. I decided against it after
learning that I would have to grind a form. Nothing wrong with this, but
it becomes more and more cost effective when you make more and more
mirrors. For a one off mirror, slumping is best for experimenting with
the method or working with a thin mirror that you don't want getting to
thin in the middle (note: I haven't made a slumped mirror, so this is
only an opinion, take it with a grain of salt)


> I know this is not true for everyone, but for me grinding your own optics is
> what makes a home built scope special.

	That's why we're here!

> I really don't know at this point what I am going to do. Dan's two blank kit
> is so tempting, and despite all the warnings about thin mirrors the siren
> call is starting to take effect.


	Well, it can work.(thin mirror) But it does add more complexity all
along the line, which can bog you down in the details. If you decide to
do this, there is plenty of help here.

	Have you thought about selling the first scope to provide funds for the
larger one? This willl give you the experience and help pay for the new
scope. Besides, making mirrors is fun, and you might not be able to stop
at just one anyhow! ;^)

	- Mike -