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The 5-element 2:1:2 design of Masuyama originated with a design of Carl Zeiss' company called the Astroplanokular.
Masuyama's production, under that label (the original "Swan" logo, by the way) used conventional glass types.
The "Pseudo-Masuyama" eyepieces from the '80s and early '90s contained some high-index glasses, so were smaller.
they were sold under the names:
Meade Series 4000 "Super Plossl" (made by Kowa)
Celestron Ultima
Orion Ultrascopic
Baader Eudiascopic
Antares Elite
Parks Gold Series Super Plossl
Omcon Ultima
Tuthill Plossl
Takahashi LE
All were made in Japan.
The Takahashi LE is still in production, as is a new version sold by Kasai called the "Astroplan".
The design has been copied by the Chinese, so there may be even more versions of these now. The Chinese versions seem to have stretched the apparent fields to 55-60 degrees, with the corresponding loss of correction at the edge.
Since most eyepieces are "farmed out" for production, it is not going to be easy to find the actual manufacturer of any of them.
The rumor is that the factory where the Masuyama eyepieces were made is still making eyepieces under other labels. Maybe. But a lot of small manufacturers have folded since 2000, due to retirement or the death of owners, so who really knows?
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