NavList:

Bill you wrote:

"Is there any reason one could not dispense with the scope and use a
zero-magnification sight tube to take the optics out of the system?"

 

Yes, you have to focus the beam. Your worry that the telescope focus is related to the index correction is wrong. Just to remind you, the whole point of doing a "table-top" test of index correction is to take the human eye out of the equation.

 

By the way, from my perspective, lasers are common-place. You can buy small ones next to the candy at the check-out in any hardware store. The nice ones with levels and on-off switches are in the back of the store. But if you find lasers "exotic" or if they seem like a cheat (assuming you like to do things in antiquarian fashion), then you can use any focusable light source with a sharp image. For example, you could project a pattern of lines using an old slide projector. I'm not saying that I recommend this --a laser is the right tool for the job.