Creede Dark Skies: Masuyama MOP and Meade Super Plössl eyepieces

Two highly-regarded telescope-eyepiece series are the original Meade Super Plössl and the Masuyama eyepieces from Ohi Optical Manufacturing company of Japan.

In the mid 1980s, Ohi Optical released a Masuyama-branded series of telescope eyepieces. Masuyama is the name of the designer and the founder of Ohi Optical. These eyepieces were a 5-element, 3-group 2-1-2 configuration, and are believed to be implementations or derivatives of the Zeiss Astroplanokular design. These eyepieces were well received and similar designs soon appeared on the market, notably Meade 5-element "Super Plössl" eyepieces manufactured by the Japanese company Kowa. The Meade eyepieces and similar offerings under other brands became known as "pseudo-Masuyamas".

The Meade eyepieces eventually devolved into a more traditional 4-element 2-group 2-2 Plössl configuration, while retaining the now-meaningless "Super Plössl" designation. Manufacturing was first shifted from Japan to Taiwan, then to mainland China. Meade Corporation is now defunct. The original Japanese 5-element versions are considered to be collectibles.

In late 2023 Ohi Optical released a new series of 5-element eyepieces designated as Masuyama MOP. There was much initial speculation about the meaning of the "MOP" acronym, but the Ohi Optical website now clearly states that it means "Masuyama Ortho Plössl".

The Masuyama nomenclature is confounding for at least two reasons. First, the original Plössl design comprises two achromatic doublets with four elements total, not five. Second, the MOP eyepieces are advertised as having an apparent field of view (AFOV) of 53°. A true orthoscopic eyepiece is limited to an AFOV of about 44°, beyond which distortion becomes evident. The MOP eyepieces are neither orthoscopic nor Plössls. Marketing, as usual, is not deterred by engineering facts.

Regardless of the naming peculiarities, the MOP eyepieces have received excellent reviews. I have three of the new MOP line as well as three of the original Meade eyepieces, which were purchased in 1988. Together they form a set spanning focal lengths from 6.4 mm to 26 mm.