What makes a good scope? Although this scope has higher quality optics than any being currently made for sextant use, the most important feature is the fork (sometimes called a rising piece) that should be exactly perpendicular to the optical axis. Each degree of error in this will add a one minute error in high altitude sextant sights. The fork on this scope is cast as part of the aluminum body, and has no error of perpendicularity. All other currently available high powered scopes are merely one-half of a binocular set, with a fork screwed onto the side. We have seen errors as high as 3 degrees on some of them.
The 7×35 Prism Telescope fits the following modern metal sextants:
- Astra IIIB
- Astra III Professional
- Cassens & Plath
- C. Plath
- Tamaya (full sized)
|To determine the fit on another sextant, the ends of the fork from its regular scope should approximately match the outlines to the right.|