uscra112 wrote on Aug 6
th, 2016 at 2:01pm:
I had to remove one of the reticle cells* from a Cummins scope I have. It was indeed held in place by a tiny grub screw going thru the cell wall from the inside.
What conceivable reason would justify such a bad idea? As opposed to a screw through the tube wall from the outside. Evidently, at some point Cummins himself must have recognized the stupidity of it, because the Cummins I have has screws through the tube wall, a total of three. Another Cummins I once had must have been constructed the same way, as I disassembled it without such extreme measures as you found necessary; I'd never have attempted it otherwise.
Quote:*The Cummins had two cells, one at each internal focal plane. The forward one is the horizontal crosshair, and the rearmost is the vertical.
And this must be why it's impossible to eliminate parallax! You can adjust the focal plane of the objective to fall on one of the wires or the other, but not both simultaneously. Trying to do so drove me mad, until I finally gave up; moreover, I remember the error as being extreme, not the little bit that can be tolerated in other scopes. The best part: I found this out AFTER I had filed two slots in a barrel for the Cummins mounts!
I have a copy of an 1892 Cummins catalog, in which there are very detailed instructions for mounting and adjusting the crosswires, but NOT ONE WORD about adjusting for parallax.