[Author Prev][Author Next][Thread Prev][Thread Next][Author Index][Thread Index]

Re: [ATM] ronchi accuracy

At 2005-12-08 17:57 -0700, jeff newsom wrote:

>    Isn't using a Ronchi program with the ruler mode very similar in 
> accuracy to using pins or a couder mask?

Suiter sez, p. 297, the "geometric Ronchi test" can't distinguish between a 
good mirror and a mirror with "unacceptable correction errors".  The main 
problem is diffraction messes up what you see.  I wrote the DIFFRACT 
simulation program in an attempt to use wave optics to model the 
diffraction patterns and turn Ronchi into the "poor-man's interferometer" - 
it didn't work.

Suiter also says that the Ronchi test sensitivity can be improved by moving 
the Ronchi screen longitudinally, measuring the movement and comparing with 
theoretical patterns.  I think Mel Bartels uses this method (but I'm not 
sure).  Suiter says, p. 296, "Unfortunately, the test is almost never 
undertaken in this manner, probably because it so closely resembles the 
Foucault test that the user was trying to avoid in the first 
place."  Perhaps John Sherman's LWT (Lateral Wire Test) version of Ronchi 
might also be an <easier> improvement.

         -- Jim Burrows
         -- mailto://burrjaw@earthlink.net
         -- http://home.earthlink.net/~burrjaw
         -- Seattle N47.4723 W122.3662 (WGS84) 

_______________________________________________
ATM mailing list http://www.atmlist.net/