ATM [Fwd: BOUNCE atm@shore.net: Admin r

[PFAFF2@delphi.com]

> setup like this how do you move the knife-edge to cut into the rays? This
> is kind of confusing to me, since the light source is also moving. I can see
> shadow patterns by moving by eye up and down behind the knife, these also
> appear to cut from the bottom or top depending on how far behind the knife I
> place my eye, this is without moving the knife at all. It is also hard to hold
> my head still, causing the shadows to dance around. It seems that it should be
> the knife and not my eye position that creates the shadows since it will be
> rather hard to measure my eye position. 
> 
> Can someone tell me a step-by-step procedure for simply finding the focal
> length with this type of tester. I appreciate any help I can get on this.
> 
>                                              Adrian Pederson
>                                              pederson@uwplatt.edu  
> 
> 
> --------------38DE713455D7--
> 
> 
I would place a small white piece of paper like a label
on the face of the razor blade ( the side facing the mirror)and focus the
return image as sharp as possible on the razor blade. Adjust the mirror and
tester position to do this. Now move the tester so that the image is projected 
on the knife edge where your eye will be. As this is a horizontal knife edge
you move it up or down to find cut off. Move it longitudinal to find the null
point for the zones. 

I also find it helpful to hold a white poster board near the RC to find the
the image than adjust the mirror to get it near the knife edge.

Bob Pfaff