Miyauchi Binon 7x50W

Mfr: Miyauchi

Date: 2004

AFOV: ~66.5 degrees

TFOV: 9.5 degrees

Eye Relief: ~20mm measured (22mm specification)

Prisms: Porro II

Weight: 1250g

Serial Number: 00069

The Miyauchi Binon is a unique binocular, a modern wide angle 7x50 with a retro design.  It is one of the few binoculars made today with Porro II prisms.  The body has an art deco design, with a burgundy leather and silver metallic finish.  Rubber rings on the objective tube help to protect the finish.  The oversized oculars are individually focused in opposite directions,  which takes some getting used to.  There are at least 5 diopters of focus travel in either direction, which allowed my near sighted eyes to reach infinity focus.  Another plus is the extended eye relief, but unfortunately the rubber eyecups do not fold far down enough for me to allow comfortable viewing when wearing moderately thick glasses.   I would have preferred sliding eyecups.

The optical designers appear to have tried to correct the overall field, though not perfectly.  There is still some rectilinear distortion and field curvature noticeable.  The distortion is not so bothersome but the field curvature is, especially for astronomical viewing.  Stars at the edge of field can be focused to near pinpoints but then the center of field is out of focus (at least with my eyes).  As Holger Merlitz has reported on his web site , the field correction is not symmetrical.  In my particular sample the upper edge of the field in both sides seems slightly more out of focus than the other directions, though this is only noticeable on close examination.  This may be due to misalignment or an imperfection in an optical surface.   There is also a slight amount of extraneous prism leakage visible.  The multicoatings do an excellent job of suppressing ghost images.  Despite the faults noted, the Binon comes closest to my ideal wide angle binocular of any modern design.

One obvious classic binocular to compare the Binon with is the B&L 7x50 Wide Field.  The B&L's single layer optical coatings are no match for the Binon's, and the Binon's edge of field is slightly better corrected.  The Binon nearly matches the B&L in eye relief but falls short in the field of view.  The B&L has the extra "wow" factor that seems to come from an apparent field of view of at least 70 degrees, a factor well known to WWII optical designers, German as well as American, but seems to have been lost to modern designers.

Link to Japanese web site with specification sheet on Miyauchi Binon.