foucault tester

I built a Foucault tester. Photos attached.

Is the telescope viewer supposed to be focused on the mirror that is being tested? Or on infinity?

From the picture, is there any way if you can tell me whether the slit for the light source is narrow enough?

I'm asking because I don't see any patterns like the ones in the book when testing a parabolic mirror. So, I must be doing something wrong.

Clears,
Joe

PS For the record: I can see the mirror darken when moving the knife edge into the field of view.

Attached Image:

more pix

Attached Image:

Focus the scope on the mirror surface.

If you can see the shadow of the knife edge but not any patterns, you may not be close enough to the radius of curvature with the knife edge. Slide the assembly closer to the mirror or further back until you get the knife at the radius of curvature and the mirror darkens all over at once as you move the knife edge into the beam.. Then you should be able to make fine adjustments to see the patterns.

hope this helps,

dan