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Will H.,

In answer to your question about which metal sextant to buy, the short answer is that, as far as I'm aware, there's no meaningful difference in quality between the top manufacturers of metal sextants (Cassens & Plath, Tamaya, Freiberger, etc.). All of their instruments are excellent and will give you similar results, and choosing one mostly comes down to personal preference -- more on that below. The Astras are also very good and will give you comparable results. Based on my limited experience with them, the Astras appear to be perhaps slightly less durable: One Astra that I've used suffered a broken clamp on the index arm, and I've heard of someone else whose micrometer drum broke after heavy use. But the vast majority of Astra users really like them and, as you point out, they're cheaper than their German or Japanese alternatives.

Two significant differences between the different metal sextants are their weight (which depends on their size and the material they're made out of) and the accessories you can buy for them. The Cassens & Plath sextants are made of bronze, which makes them quite heavy. The Astra IIIb and Freiberger sextants are made of aluminum, which makes them lighter (quite a bit in the case of the Freiberger “yacht” model). And the Astra Professional and Tamaya sextants have an aluminum frame and a bronze arc, which puts their weight somewhere in the middle. Some believe that a heavier sextant makes it steadier and gives better results, and others believe a lighter instrument is less tiring to the arm and gives better results. I’m in the latter camp, but it’s really a personal choice (maybe I have weak arms 😉). The various metal sextants also come with different accessories. Cassens & Plath, Astra (and, I believe, Tamaya) use a “standard” attachment for the telescope, which means that you’d be able to swap out scopes, attach an artificial bubble horizon, or other accessories from various makers more easily. Freiberger uses a proprietary attachment, which means you can use only their telescopes and accessories.

I guess the bottom line is that, if you’re looking for a serviceable metal instrument that’s versatile, relatively affordable, and will give you good results, the Astra is a good choice. If you like precision engineering and “beautiful machinery” that will last a lifetime, the finish on the German instruments would probably be more satisfying to you. Among the latter, if you’d like a bronze sextant, Cassens & Plath is the way to go, but if you’re looking for an aluminum instrument, then you might want to look at Freiberger.

On a more general level, if you’re looking for some general tips and thoughts about sextants and their accessories, I recommend “The Sextant Handbook” by Bruce Bauer. It’s a short, practical guide by a working mariner, and you might be able to check our a copy from your local library.

I hope this helps,

Denis