From: "Dan Chaffee" 
To: 
Reply-To: "Dan Chaffee" 


>You will want to build several spherometers as Dave indicates.  Difference
> in them is the radius you measure to.  Also several dial indicators are
> helpful.

I don't understand why. I made a very successful 7" achromat with one
and only one spherometer and NO dial indicator. It consists of a micrometer
attached to the end of a lever arm that yields a movement 33% of what the
micrometer indicates. The accuracy is easily under .001" and the two
'feet' balls contact very nearly to the edges of the lenses
giving the maximum depression that can be measured (and resulting in better
accuracy  than if measuring a smaller segment of the curve). By reversing
the direction of the motion of the lever arm and placing a bolt near the
pivot, it doubles as a very sensitive wedge checker. There is no lateral
color that I can see in this lens, which means wedge is as good as it needs
to be. I had the micrometer and I think it set me back $10 for the aluminum
to make the lever arms and $4 or so for several ball bearings for the
points and to calibrate with.

Dan Chaffee

--- BBBS/NT v4.00 MP