Re: [ATM] fringe testing a convex and concave surface together.

[Mike Lockwood <melockwo@uiuc.edu>]

Hi,

Dale Eason wrote:
> There were recent questions about how to test convex
> and concave surfaces together.  I just ran across this
> web page.
> 
> http://www.geocities.com/stressedglass/fringetesting.html

Those are nice fringe testing photos, and they give a good idea about 
how to interpret the fringes.  Makes a very good short tutorial.  A 
good page to bookmark.

However, from the viewpoint of the photos in the site above, the 
fringe pattern will be somewhere between slightly and significantly 
distorted, depending on the thickness of the air gap.

Viewing of the fringes should be done from directly overhead (using a 
45-degree mirror allows viewing the directly overhead perspective from 
the side), in order to see the undistorted fringes.  One shouldn't be 
able to see the sides of the pieces under test.

Additionally, fringes should be viewed from a distance of at least 10 
times the diameter of the pieces away from them in order to get an 
accuracy of 1/10 wave.  Typically I try to photograph the fringes with 
my digital camera from about twice this distance away.

	Mike Lockwood

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