Hello. Would anyone be able to confirm how an aperture tube site functioned? My thinking is that the front of the tube was fixed and must have had a post while the rear of the tube had adjustment for windage and elevation? The top rifle in the illustration is similar to what I am thinking. Thank you. Kurt

I think you understand it correctly. There would be a post or ring at the front, and the rear of the tube would be deflected by vertical and lateral external adjustments.

The rear would have an aperture to aim through and possibly a corrective lens.

I have never used one, but a modern version used to be offered on .22 B.S.A. Martini International match rifles.

I assume that the tube was intended to eliminate varying light conditions from the side or above, but otherwise I can see little advantage over the more usual front short tube and aperture rear sight.

Some of these tube sights came with interchangeable apertures both front and rear. So you could adjust the aperture size at the rear, and the type and size aperture at the front. Other than magnification these adjust much like a long tube scope, but work like iron sights.
I've owned one Unertl tube sight, and a couple unknown maker's tube sights. Only restriction I've found is they don't adjust enough to shoot much past 200yds.

Thank you Parabola and Vall for your answers. Just what I wanted to know.

I have a Martini with a Unertl tube sight which I have removed. I am looking for the ideal American gun to install the tube sight on. Any suggestions?

My choice would be almost any American single shot from the late 1800's or early 1900's, that you intend to shoot at 250 yds. or less. They look very appropriate on these rifles, and the tube sight works great out to this distance, with enough adjustment in the mounts.

Thanks, more suggestions are welcome.

eightbore, I came to the tube sight while trying to create an aperture sight for my flintlock rifle. I've been hunting with it a lot during PA's late season and realized my difficulty seeing the partridge type sights. While working on a rear aperture, that I have installed but have yet to test, I had a piece of cut off aluminum arrow shaft and looking through it realized the good sight it might make. I then remembered seeing a tube sight on an original flintlock rifle somewhere. I also came across some Martinis with tube sights in my research.