Re: [ATM] Ain't got no shperometer

["Bob May" <rmay@nethere.com>]

Pete, the accuracy of a foucault tester lies in what it is doing,
not how precise you make the movements of it.  The simplest of
testers is merely a block of wood with a edge that is fairly
straight - a filed edge on a piece of metal or even a fine
grained piece of wood - and a small light source or a larger
light source with a similar KE at the same angle as the testing
KE and of the same direction - the slitless tester version works
on this principle.  With just that, you can't tell if you have a
paraboloid but  you can see spheres quite nicely.  Add in a
device to measure the motion of the KE and you can then measure
the different zones for a paraboloid. The accuracy of the
measurinbg merely needs to be more accurate than the difference
in zones.    Measuring to a thousandth of an inch is quite good
and you really don't need more than that as your eye usually
can't see anything less than two to fivce thousandths of an inch
in difference in position of the KE, depending upon the zone you
are measuring.  The tester design that the Stellafane site has is
quite good enough for anybody   Build the measuring and pushing
points square and there will be no problems measuring any surface
within reason.
Bob May
Due to the large volume of SPAM thaat I'm getting, add an open
square bracket to the subject line or my spam filter will reject
your post~
rmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net
Replace the obvious words with the proper character.

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