Re: [ATM] Rough grinding, focault test

[Ken Hunter <atm_ken_hunter@yahoo.com>]

To answer a few of the recent questions about when to start testing (Focault)
   
  The best you can expect from testing during rough or fine grinding is a close approximation to the focal length. At this stage, some water or other liquid is sprayed onto the surface and immediately the sun or high intensity light is bounced from the liquids surface to find the focal length. If using the sun, the focal length is found directly at the best "focus" point. If using a light source (not at infinity), then the focal length has to be calculated. 
   
  The Focault test is done on a fully polished surface to judge the shape of the curve. At this stage, there is not enough resolution to do a Focault test on the glass. 
   
  Ken Hunter
   
  PS... Please trim your posts to reflect only the topic being discussed as done below.
   
  

Miguel <emiliarodriguez@bellsouth.net> wrote:
  Hello,

Thank you Bob May for your reply to my linear resolution question. I just 
saw a post a few emails ago about a focault test at the rough grinding 
stage, 

 		
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