NavList:

Paul Dolkas you wrote:

The A-12 had a different type of light path than the Kollsman – you don’t view the star through the cell (see attached).  Rather than using a mirror to reflect the light up into the cell from below,  you could use a prism to bend it down to view the cell from above. Placing the lamp behind the cell would give you a dark circle against a bright background. So it could be done.

 Paul

I’ve changed this to a new thread.  I thought, just for fun, could you make a substitute chamber for an A12 with the upper glass at the bottom and the bottom glass at the top, and with a ball in it, probably with a bit of extra separation between the glasses?  First thing was to check the sun came through a dark object.  I cut a small circle from sticky-backed plastic and stuck it onto the top of the chamber (photo one).  Yes the black circle shows up OK from the eyepiece.  Then the Sun came out for a few seconds, and yes you can see the Sun through the black disc OK. I’m afraid photo two’s not very good because I couldn’t hold the sextant steadily enough with one hand, and I had no way of checking where I was aiming.  Also, the camera didn’t like all the light creeping around the edges if the shades.  Tonight if there’re no stars, I’ll try taping a led to the garage door to see if you can see that through the black disc.  Then we need someone to contribute a dead A12 chamber in the cause of science.  If afraid I’ve only got the one, and that’s too precious to start mucking about with.  DaveP