Re: ATM 8" f3.8 -- Worthy project?

[Dwight Elvey <elvey@hal.com>]

"Bob May" <bobmay@nethere.com> wrote:
> 
> Interesting sounding idea but I do believe that the wire and the slit need
> to be pretty close to each other in width?????  The reflection of the laser
> from the wire is an intriguing one tho.  Does anybody have any experience
> with the setups of the wire test that would indicate whether this would
> work?  A narrow slit and a wide wire is basically what is being stated.

Hi Bob
 In the wire tester the source needs to be smaller than the wire
or you begin to see around the wire to the source and lose
contrast. I think that even with a wide wire, you can still
get both edges with a slit that is almost as wide as that
wire. The problem here is that I think a small loss in accuracy
of the measurement happens because of the angles relative to
the axis of the mirror. I'm not sure how much this would be
in the case of the 0.0015 wire but I'm sure it could be worked
out. It would be interesting to see what change this
would make as the wire got wider ( Are you listening Jim B. ).
Having the larger wire also means that contrast will be
lost faster for rough surfaces of the mirror but I don't
think this is a big issue.
 You do need to have an adjustable slit source. This way you
can adjust the shadow size to be practical.
Dwight