Kasai Trading 2.3x40 Wide Field Binoculars with 28° True Field of View


Kasai Trading 2.3×40 Wide Field Binoculars with 28° True Field of View


WideBino28 is a peculiar star-gazing instrument yielding 28-degree field of view with your both eyes.


WideBino28 is a peculiar star-gazing instrument yielding 28-degree field of view with your both eyes. While most constellations can be captured within a field, 1 or 2 magnitude darker stars can be detected – you must feel as if your eyes are suddenly “doped”. Since early 90’s, this unique device has been enthusiastically loved by huge number of Japanese astronomers. Now it’s your turn to experience this marvelous view.

Optical Design

Basically the field of view of Galilean opera glasses is very small. The only way to widen it is to use extremely fast (f/2 or faster) objective lenses, but normal achromat doublet lenses of such fast f-ratio show strong aberrations and it’s practically impossible to be used for visual observations. The optical design of WideBino28 is epoch-making as adopting 2-group 2-element meniscus objective lenses and 1-group 2-element cylindrical eyepieces, achieving edge-to-edge very flat widefield with very little aberrations. You can enjoy pinpoint star images within full field of view. Every surface of the lens element is broadband multi-coated to enhance the transmission rate, and all the inner walls are thoroughly threaded and blackened to eliminate the stray lights.

Mechanical Features & Accessories

Most parts of max. 123mm width / 255g weight compact body are made of metal. Individual focusing. Front & rear dustcovers are standard. Comes with a neckstrap and a soft carrying case with a shoulder strap and a belt loop.

General Aptitude

The extremely wide 28-degree field of view brings overwhelming feeling of liberation, having a great aptitude for night sky observations. It can capture one constellation within a field of view, with 1 or 2 magnitude darker stars emerged – it must be the best and the only one device that can do a “feat” for the observes to see the whole figure of a constellation with scattered deep-sky objects in it. Especially, the beautiful images when seeing the Milky Way are beyond expression. Once you see it, you must become addicted. Please do have such a peculiar experience as “constellations come closer to you”.


Clear Aperture: 40mm
Power: 2.3x
Field of View: 28-degree
Max. Dimensions: 123mmx40mmx50mm
Weight: 255g
Interpupillary Distance: 52mm – 73mm
Diopter Range to focus infinity: > -6 diopter
Focusing Mechanism: IF
Standard Accessores: Front & Rear Dustcovers, Neckstrap, Soft Carrying Case
NOTICE (1): Galilean telescope system has no eye-relief. The best way to see the widest field of view is to “press” your eyes close to the eye lenses. Therefore, it’s essential to see through WideBino28 with your naked eyes. Very strongly shortsighted eyes, as – 6 or less diopter, can’t reach the infinity focus. In such cases wearing contact lenses is recommended.

NOTICE (2): The field of view of Galilean telescope system varies by the pupil diameters of the observer. 28-degree can be obtained when the pupils are opened maximum (usually 7mm). In brighter observing conditions or older observers, a smaller exit pupil will result in a reduced true field of view.

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