From: "Dwight K. Elvey" 
To: atm{at}shore.net
Reply-To: "Dwight K. Elvey" 


>From: J-Engineering 
>
>Hi All.
>
>I am working on laying out a Ronchi and a Foucault tester.  The design
>is such that the beam emerges from a hole in front of frosted glass.
>How big should the hole be?
>
>The beam returns through a 12 mm hole.  How close should these two holes
>be?  Is 12 mm center to center OK?  Mirrors will be in the f/5.5 to f/7
>range.
>
>I am using a JMI focusser as a linear guide so the tester will need to
>fit in a 1-1/4 inch dia adapter.
>
>Thanks for your help!
>--
>Ray
>Ray{at}J-Engineering.com

Hi Ray
 You need to tell us the length of the tube on the focuser.
The 5.5 will be the limiting factor. Both holes would need to be within a
circle formed by the entrance of the focuser tube and a 1:2(5.5/2)
triangle, rotated around the inside of the bore. The increase by 2 is
because we are at ROC and the /2 part is because we are talking diameter
and not radius.
 As an example, lets say that the distance from the knife
edge was 2.5 inches to the front of the focuser tube. Now, let us say that
the diameter of the focuser tube was 2 inches. 2.5 / ( 2(5.5/2) ) = .455
inches.
 This means that both holes would need to be within
a circle that was ( 2 - 2(.455) ) = 1.09 diameter. The 2* is because this
cuts in from both sides.
 This is enough space for your two 12mm holes.
You don't really need two holes, though. You just need to baffle the light
source so that it doesn't shine into your eye while looking past the knife
edge or through the Ronche. This can be done with a single large hole. In
the above example, the 1.25 adapter could be that hole.
Dwight

--- BBBS/NT v4.00 MP