Re: ATM ronchi-confused-bob may

["john" <jp@premier1.net>]

bob,thanks,
i let the mirror sit overnite,
got my tex readings on a 4zone mask,
1)0.0000
2)0.1600
3)0.5800
4)1.7600
went two trips aroun the barrel with a 8inch tool,
let it sit,
second readings,
1)0.0000
2)0.1300
3)0.5500
4)1.6500
,
it looks to me that i need to knock the 3 and four zone down some,
be aware that im very knew to the focalt testing,
i run my measurements at each zone 3times checking on how close i come
each time,
,
experience can be a frustrating teacher,
thanks,
jep.
----- Original Message -----
From: "Bob May" <bobmay@nethere.com>
To: <atm@shore.net>
Sent: Tuesday, April 10, 2001 11:04 AM
Subject: Re: ATM ronchi-confused


>
> The images with the Ds in them are more for reference as to what the image
> looks like that close to the center.  Better to go further from the ROC
with
> the grating and see what the lines look like as they curve.  The problem
> with the Ronchi Test is that you need to be very careful with the
> positioning of the grating and in reading the lines or you won't be seeing
a
> Paraboloid but rather a Hyperboloid or Elipsoid curvature.  The Ronchi
Test
> is best done as a check on the smoothness and evenness of the curvature
> rather than the qualititive test as to exactly what figure that you are
> looking at.  The Foucault Test is excellent for finding out if the various
> zones are the correct ROC but relatively poor for finding out whether the
> curvature changes are correct.  The two tests actually compliment each
other
> and my process is to get the zones right and then use the Ronchi Test to
> insure that the shape of the mirror is correct.  Just using the Foucault
> Test, especially when not enough zones are done, can produce a very zoney
> mirror while the Ronchi Test has a very difficult job saying when you have
> the correct Paraboloid curvature.
> Usually when testing, I use zone 1 and 5 of a 5 zone mask to tell if the
> mirror meets the Paraboloid change for the ROC and then look at the
overall
> shape of the mirror for whether it is a smooth and correct shape.
>
>
>