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Masuyama 3" Eyepiece with 52° AFOV - 80mm # MOP-80

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Brand Masuyama
Part Number MOP-80

Product Info

Manufacturer Description

A brand new design that offers long focal length telescope users low magnification, a wide field of view and an immense actual FOV!

In collaboration with Mr. Masuyama of Masuyama eyepiece fame, Kokusai Kohki of Japan went out on a limb in introducing a truly new eyepiece, the 3 inch barrel size Masuyama 80mm. This eyepiece is aimed specifically at the many private and public owners and users of long focal length telescopes who would like to greatly reduce the intrinsic high magnification of their telescopes, while also significantly widening the FOV they are able to attain at this low magnification, gaining striking celestial views reminiscent of those seen through similar aperture dobsonian telescopes.

Although an 80mm focal length eyepiece is not entirely unheard of, an 80mm eyepiece of 2 inch aperture imparts a narrow FOV that hardly gets the blood pumping, and the oohs and ahhs coming. In contrast, the 3 inch aperture Masuyama 80 goes far beyond the current 2" (50.8mm) paradigm by boldly going where few eyepieces have gone before, into the parallel universe of 3" barrel width (76mm) eyepiece design. A peculiar new universe that now allows low magnifications AND wide fields of view.

The Masuyama 80 is not a mere extension of the previous Masuyama design but a brand new design that allows it to perform with excellent image sharpness from center to edge, and little to no light loss at the field edges. Viewing through a C11 at 35X, with over 1.5 degree AFOV, this eyepiece sends long focal length telescopes into the realm of RFTs and short f/l Newtonians. With a field stop diameter of 70mm, at a 52 degree apparent FOV, the huge image combined with the amazingly lowered magnification creates a feeling of a much larger area of space being viewed that what the modest number 52 would suggest. After all, how many full moons would fit in a 1.5 degree actual field of view?

Each hand made Masuyama 80 is carefully and lovingly designed and manufactured in Tokyo. Each eyepiece is fully tested before shipment and is anointed with its own serial number. Production runs are limited and only 20 eyepieces are currently available for sale. Each air to glass surface is fully multi-coated. A rubber eye guard insures optimal eye positioning. And a large "tire" placed around the bottom half of the eyepiece, covered in a non-slip rubber rollet, provides a secure hand hold for the hefty 1.7 Kg (3.74 lb) weight of this massive eyepiece. Each eyepiece also includes its own aluminum trunk case.

Is the Masuyama 80 a good fit for shorter focal length telescopes? Well, the Masuyama 80 is not for everyone, but as long as your telescope is equipped with a 3" focuser sleeve, the Masuyama 80 will provide excellent, distortion free views as well. For example, when attached to an APM 130/F6 CNC-LW telescope, the Masuyama 80 provided surprisingly clear and fresh images at the mere 9X magnification that this combination produces. No edge distortion or vignetting was seen, and images from field center to edge remained sharp and contrasty. So yes, the Masuyama will also work well with shorter focal lengths.

Now, while this was a valuable experiment, short focal length telescope owners have many other options available to get low power and wide fields without the expense (or the massive size) of the admittedly high price of the Masuyama 80. The true value of the Masuyama 80 remains with long focal length telescope users who want to gain a wide field, low power window to the universe similar to those provided by our beloved dobsonians.

To help make the transition to a 3" focuser easier, Kokusai Kohki also developed a low cost 3 inch star diagonal mirror system that includes the 3" adapter sleeve for easy attachment to your (larger) SCT tube's (larger) visual back. This 3" diagonal is available separately from Agena here (link coming soon).


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Apparent Field of View 52°
Barrel Size 3" (76mm)
Bolt Case Included None (Includes Aluminum Trunk Case)
Height (with Eye Guard) 212.4mm
Max Width 110mm
End Caps 2
Field Stop Diameter 70mm
Focal Length 80mm
Lens Elements 3
Rubber Eye Guard Yes
Blackened Lens Edges Yes
Manufacturer Masuyama
Eyepiece Focal Length 40.1mm and Higher
Eyepiece Field of View 51 - 60 degrees
Eyepiece Series Masuyama
Barrel Type Smooth sided