Re: [ATM] Polish / figure question

[William Marriott <bmarriott@pacbell.net>]

Hello;

Well, I thought I would chime in here, despite the
fact I have not made a binoc scope, so my thoughts are
in theory only. 

When you say your mirrors are f 5.097, and I am
assuming when you say 12", that you may mean 12.5", if
standard diameter Pyrex,if not, no matter, just
different numbers, that means the focal length is
63.7125", or R=127.425  So, this would be pretty darn
difficult to measure to that accuracy with a knife
testing rig, are you measuring with a spherometer?  If
so, how many places does it measure to?

When I try to hit a focal length right on the nose, I
use a very accurate spherometer that can measure to a
fraction of a .0001"
It is marked in tenths, but being very clean and
carefull, you can say its 1/4 of a tenth, or 1/3rd of
a tenth, etc. 

When you are polishing out your glass, it is much
easier to change the fl by going more concave, than
trying to go less concave, especially with a machine,
by hand I am not sure. If you can get them to read the
same with an accurate gauge, I think you would be
halfway there.  Then when polishing, I would try to
work center and edge equally, maybe going back and
forth between the two pieces of glass, alternating MOT
and TOT, and once fully polished out, trying to get
the less concave of the two, if there is one, to drift
into spec by working the center more. Once there, one
would think that figuring would not change anything,
unless you had to go back to a sphere several times

I do not know the allowable difference in fl for a
binocular scope, so maybe I am being too detailed.

So, that is how I would approach it, if I ever make a
bino scope, I will find if I am correct or not.

Best regards

Bill Marriott
V-A Optical Labs

PS, Gugloz 64 at 70 deg.F, sounds like the perfect
combination.



--- j h <quantemlp@hotmail.com> wrote:

> Hello to everyone,
> 
> I have a quick question and before I proceed I would
> like some input as to a 
> direction.  I have ground out 2 mirrors for a bino
> scope.  Mirror a and 
> mirror b, both 12" f/5.097.  I have used one tool to
> make both mirrors and I 
> am now at the polishing stage (excitment building
> here).  Would it be good 
> to polish one mirror out and then the other mirror
> out before figuring, 
> or.......... polish for one hour on mirror A and
> then one hour on mirror B 
> continuing the altering processess until both are
> polished out completely.  
> I understand that figuring of course would be one
> mirror at a time.  I am 
> using a full size lap gou 64,  room temp is about 70
> degrees where I will be 
> polsihing.
> 
> thanks to everyone for making this an enjoyable list
> to belong to.
> 
> Clear skys,
> charles
> 
> 
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
> 

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