Binocular Definitions - Vixen Optics

The explanation of the terms that describe the functions of binoculars, fieldscopes and etc. The meanings of the image logos in the product lists like Pict:Dach (Roof) Prism Pict:Tripod Attachableare also explained here.   

By Vixen Optics

Prism Types

There are "Porro prism" invented by an Italian, Porro, and "Dach prism" that uses roof prism (roof=dach in German).

Pict:Porro Prism Porro Prism
It boasts a high cost performance but the body tends to be large.
Pict:Dach (Roof) Prism Roof Prism
Roof-prism binoculars that are more compact than Porro-prism binoculars with the same aperture size can be produced because the optical axis draws a straight line from the eyepiece lens to the object lens.
Prism Material

Prism is made of the crown glass with a high refraction rate, such as borosilicate crown, "BK," and barium crown, "BaK."

The material for general types of prisms.
The material for the highest class of prisms which has an excellent optical function. It produces an image without any blur even near the edges.
The material for high quality prisms which yield outstanding optical performance. It has higher refractive index than BaK4 and produces extremely clear and sharp edge-to-edge image without loss of light as a result.

Various kinds of coatings are applied on lens or prisms. The coating works to reduce the loss of light and to product a bright image. The optical functions are different in different methods or kinds of coating.

Pict:Magenta Coating Magenta Coating
Coated Parts…Lens surface
It reduces the loss of light and produces a bight field of view.
Pict:Full Coating Full Coating
Coated Parts…All surface of lens (object lens or eyepiece lens)
It reduces the loss of light by large amount.
Pict:Multi-Coating Multi-Coating
Coated Parts…Lens or prism
Multi-layer coating with more than 3 layers is applied and yields a high contrast in image.
Pict:Fully Multi-CoatingFull Multi-Coating
Coated Parts…All over the surface of lens (object lens or eyepiece lens)
Multi coating is applied and the bright field of view with a high contrast is produced.
Pict:PFM Coating PFM(Perfectly Fully Multi-) Coated
Coated Parts…All surfaces of lens and prisms (object lens or eyepiece lens) are multi-coated, and a high contrast is obtained.
Pict:Phase Coating Phase Coating
Coated Parts…The spacial method of coating that corrects the aberration in Dach prism. It prevents lens flares and dramaticalley improves the resolution, producing a high contrast.
Pict:H.R.D Coating H.R.D. Coating (High Reflective Dielectric Coating)
H.R.D. coating that is applied to a reflective surface of the subsidiary prisms by dielectric coatings strongly enhances the reflectivity and produces outstanding crisp image.

Lens Material
Pict:ED Lens ED Lens
ED(Extra low dispersion) glass is used in this special lens, and a sharp image with few coloring blots is produced.

Lens Types
Aspherical Lens
It corrects the curvature aberration created around of edge of a field of view, and a sharp field of view with few distortion is created.
Object Lens Effective Diameter

Onject lens is the lens that is placed closest to the object to view, and the effective diameter is the diameter of this lens. The larger the number, higher the light gathering power, and the binoculars and fieldscopes with superior resolution are produced. In addition, the size of the body becomes large as the effective diameter becomes large.

Fieldscope Types
Pict:45-Deg Inclined Viewing Type 45°Inclined Viewing Type
The eyepiece lens is tilted at 45°in the optical tube. It makes it easy to view an object located at a high altitude.
Pict:Stragiht Viewing Type Straight Viewing Type
The optical tube and eyepiece lens are placed on the same axis in this design. It is easy to find an object and to operate when a camera is installed.

Actual Field of View

It is the field which you can view without moving the binoculars or fieldscope and is expressed as an angle. The larger the actual field of view, the wider the field which you can view.

Apparent Field of View

It is the field of view seen when you look in the binoculars and is expressed as an angle.
Apparent Field of View = Actual Field of View ×Magnification

Pict:Wide AngleWide Angle
If the apparent field of view with 65°or wider, it is called a wild-angle type. A wide field of view can be powerful in watching sports games such as soccer and rugby games or small birds that are fast moving objects.
Pict:Extremely Wide Angle Extremely Wide Angle
The apparent field of view wider than 75° is called an extremely- wide-angle type. It obtains an image of almost an entire starry sky with its very wide field of view.
Field at 1000m

The field seen at 1000m away without moving the binoculars or fieldscope is expressed in meters.

Exit Pupil

It expresses the diameter of an object lens seen through an eyepiece lens. The larger the exit pupil, the brighter an image.
Exit Pupil = Object lens effective diameter÷Magnification


The value obtained by squaring an exit pupil is called "brightness." The larger the brgihtness, the brigther an image.

Eye Relief

The distance between the eye and the eyepice lens when the entire field of view is visible when looking in the binoculars. The longer the eye relief, the less stress felt in the eye.

Pict:High Eyepoint High Eyepoint
The model with the eye relief longer than (or equal to)15mm.

Near Distance

The shortest distance from the eye to the image of the object focused in binoculars or a fieldscope. (It differs from person to person.)

Pict:Zoom Zooming Type
The magnification can be varied according to the object you are viewing. An image looks large with a high magnification, but the field of view appears a littl darker.

Special Processing
Pict:Waterproof Waterproof
It is the design to protect the optical tube from becoming wet even in the rain or snow. It is suitable for outdoor use when the weather is unstable.

Tripod Installation

During long-term observation or when the binoculars with high magnification are used, it is recommended to fix them with a tripod to obtain a stable field of view.

Pict:Tripod Attachable Tripod can be attached
The binoholder is provided for installation of tripod.
Pict:Tripod Attachable(H) Tripod can be attached (MH)
A tripod can be installed by using "Bino-holder MH (Tripod Adapter MH)" sold separately.
Pict:Tripod Attachable(H)(MH) Tripod can be attached (H) (MH)
A tripod can be installed by using "Bino-holder H (Tripod Adapter H)" or "Bino-holder MH (Tripod Adapter MH)", which are sold separately.
Pict:Tripod Attachable(V) Tripod can be attached (V)
A tripod can be installed by using "Binoholder V" which is sold separately.