RE: ATM 8"f/7 astigmatism

["CSC" <optic@gwi.net>]

I make several pinholes on the same foil, one obviously huge.  This makes it
easy to locate the return beam.  the other pinholes are smaller, and on or
two is usually optimal in size.

Sort of like looking at an open cluster.

Remember that lateral separation will introduce some astigmatism, so make
the mirror holder such that you can rotate the mirror to isolate what's on
the glass, and what's in the setup. I null test spheres using a laser
pointer without it's focusing lens as a source.  I have astig in the setup
but I know what it is.

Reflecting light off a ball bearing right at the eyepiece will eliminate the
astig from the setup, as will other clever ideas using a beam splitter,
microscope slide, etc.

Colin

-----Original Message-----
From: owner-atm@shore.net [mailto:owner-atm@shore.net]On Behalf Of
david.a.stevens@gm.com
Sent: Tuesday, September 30, 2003 12:03 PM
To: Atm
Subject: RE: ATM 8"f/7 astigmatism




Thanks for all the responses,

I have determined  the mirror is astigmatic and not stressed. I still have
to determine how astigmatic it is. After looking in ATM #2 page 70 on
astigmatism I have opted to go with test setup #2. I have made a fixture
for the eyepiece and a separate fixture for the pinhole.
The only thing I have to do is to attach the eyepiece and the maglight w/
pinhole made from aluminum foil.
 Has anybody else tried this??
How hard is the setup i.e. finding the return reflection in the eyepiece??

I am doing this both as an excercise, and to find out how much astig I have
to determine if I have to go back to grinding.


Thanks,

Dave



                      "CSC"
                      <optic@gwi.net>          To:       "Atm"
<atm@shore.net>
                      Sent by:                 cc:
                      owner-atm@shore.n        Subject:  RE: ATM 8"f/7
astigmatism
                      et


                      09/24/2003 05:40
                      PM
                      Please respond to
                      "CSC"







Elegant!  Yeah, try that.

Lenscrafters start with blanks that already have the cylinder on the back
side.  They generate the front to whatever diopter you need.

Drop in some day and some young tech will be excited to give you a tour.

Starts the mind working.

Colin

-----Original Message-----
From: Richard Schwartz [mailto:richas@earthlink.net]
Sent: Wednesday, September 24, 2003 3:24 AM
To: CSC
Subject: Re: ATM 8"f/7 astigmatism


I don't know if this would work, but what happens if you polish on an
eliptical pitch lap without rotating the mirror?

Somehow I can go to lenscrapters and have astimatism-correcting eyeglasses
made while I wait.   How does THAT work?   And while we're at it, how the
blazes do they make blended bifocals and trifocals?

. . . Richard

----- Original Message -----
From: "CSC" <optic@gwi.net>
To: "Atm" <atm@shore.net>
Sent: Tuesday, September 23, 2003 12:59 PM
Subject: RE: ATM 8"f/7 astigmatism


>
> I think it will take a long time to gradually polish it out.
> Toroidal mirrors are made by NOT rotating the tool/mirror in relation to
> each other, but you need to understand which way the astigmatism is
> oriented.  I would think that polishing with tool on top across the short
> radius axis to lengthen it, and mot across the long axis to shorten it
would
> get it in fairly roughly.
>
> Probably the best way to test would be to use an artificial star
(pinhole)
> with the foucault and an eyepiece.
>
> After getting the image reasonably round, it would be a matter of some
long
> polishing spells to smooth it all out.
>
> I did try once to polish out some astig, takes work and gumption, and I
> wasn't that successful...rough results.
>
> colin
>
> -----Original Message-----
> From: owner-atm@shore.net [mailto:owner-atm@shore.net]On Behalf Of
> david.a.stevens@gm.com
> Sent: Tuesday, September 23, 2003 7:48 AM
> To: atm@shore.net
> Subject: ATM 8"f/7 astigmatism
>
>
>
> Hello everyone,
>
>
> OK, I have made a new lap last night and it is pressing as I type. I
> beleive now that the mirror is astigmatic, my question is how to get rid
of
> it??
>
> I am going to assume the astigmatism was polished in and not ground in.
>
>
> Any suggestions would be appreciated,
>
> Thanks,
>
> Dave
>
>
>
>
>
>