A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Ed Popko
Date: 2020 Feb 9, 03:44 -0800
I recently had my Link Aviation A-12 bubble octant refurbished, the bubble chamber was dry and a film of crud clouded the viewing window. Some other minor items with the battery cylinders were fixed as well.
After taking more than a hundred shots from a stable platform (slouched over a rubber yoga mat over hood of car), I am impressed with what the A-12 can achieve. Frank's GPS Anti Spoof Pro app is a huge help when using this octant. It provides body Hs for preset, time pause, GPS lat/lon, has Limb/Horizon settings for Center of body and Bubble. In addition, it computes Hs based on IC, EH, temp and pressure so you have a way to compare your sight.
I didn't grow up in the video game era so centering the bubble and body took some getting used to. The most difficult part for me was reading the vernier. These poorly lit tick marks are really tough on the eyes.
Below are the pros/cons I found. I would be interested in the experiences of other A-12 users and any advice on good technique:
- Small, compact, rugged construction
- Day/night use
- Easy to use
- Capable of 1' Hs accuracy with care and stable surface
- Sun and full moon fits bubble perfectly
- Eyeglass friendly, rubber eyecup if flat and one can get their glasses right up to the viewer
- White recording drum turns in intuitive direction for raising or lowering body in viewer
- Filters easy to manage
- Easily adjusted bubble illumination
- Requires a steady platform for good results, don't know how those air navigators did it (hats off to them)
- Narrow field of view requires pre-calculation of Hs!
- Vernier and averaging drum night-light not effective
- Vernier very difficult to read, very fine markings
- Only bright stars are usable, bubble chamber viewing window frost obscures dim ones, Venus, Sirius, Aldebaran, Pollux OK
- Difficult to determinme IE. Polaris is not very visible.
- Easier to use Air Almanac and Q factor for determining IE with Polaris than Nautical Almanac's four-part correction
- No cross hairs to center bubble!!
- Centering non-full moons is challenginin bubble is challenging
- Averaging drum with graphite tick marks