[ATM] Re: Spherometers

[jpcrombie at pei.eastlink.ca (James P Crombie)]

Robert
  There are quite a few sites with info on spherometers.  many more on a 
google search.

http://www.turbofast.com.au/astrotel/spherometer.html
http://www.city.ac.uk/optics/optics/downloads/LF/LF3.pdf
http://www.starastronomy.org/TelescopeMaking/Links/  (scroll down to 
spherometers)

The smaller the spherometer the less accurate it will be,  You should 
make it as large as possible to fit your lenses.  Depending on your 
measuring instrument, a piece of thick window glass will work for a 
reference or if you want something a little better, a granite surface 
place can be gotten for unde $30 for a 9x12" plate from some of the 
discount machinery suppliers like Harbour Freight or Grizzly tools in 
the US or BusyBee tools or LeeValley here in Canada.