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 are also explained here.

Prism Types

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

Porro Prism

It boasts a high cost performance but the body tends to be large.

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."

BK7

The material for general types of prisms.

BaK4

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.

Coating

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.

Magenta Coating

Coated Parts…Lens surface
It reduces the loss of light and produces a bight field of view.

Full Coating

Coated Parts…All surface of lens (object lens or eyepiece lens)
It reduces the loss of light by large amount.

Multi-Coating

Coated Parts…Lens or prism
Multi-layer coating with more than 3 layers is applied and yields a high contrast in image.

Full 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.

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.

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.

Lens Material

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

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.

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

Wide 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.

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

Brightness

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.

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.)

Magnification

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

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.

Tripod can be attached

The binoholder is provided for installation of tripod.

Tripod can be attached (H)

A tripod can be installed by using "Binoholder H" which is sold separately.

Tripod can be attached (V)

A tripod can be installed by using "Binoholder V" which is sold separately.

Magnification

The most important factor in choosing the right binoculars is magnification. However, it is not always true that the binoculars with high magnification are more worth than those with lower magnifications. It is the best to have binoculars with magnification up to 10x if you observe with your hands. The images seen through the binoculars with magnification higher than 10x would be affected by shaking of the hands. Also, the field of view becomes darker and narrower as the magnification becomes higher.
For fieldscopes, magnification is changed by swapping the eyepiece lens. There are also zooming types which you can vary the magnification according to the object to view. For these type, the field of view is a little darker though the object appears large when high magnification is used.
For example… <The recommended magnifications for different circumstances>

For watching fast-moving small birds on hills or a plateau.

6〜10x

For observing a waterfowl in the tideland or seashore

10〜30x
You can observe by fixing binoculars on a tripod.

For trekking in a plateau or climbing mountain

6〜10x

For going camping by car

7〜10x
It can cover from nature observation to star watching.

For watching soccer, rugby, or ski competitions

8〜12x
The most suitable for a large track field.

For watching basketball or volleyball games

6〜8x
The shaking by hands is not noticeable.

For seeing a night sky casually by holding binoculars with hands

7〜10x
It is the appropriate magnification for seeing star clusters or nebulas or lunar craters, and it is not largely affected by shakings of the hands.

For astronomical observation

10〜30x
To be used With a tripod. A fieldscope is also suitable.

For concerts in a dome or any large event hall

8〜12x

For watching a play or an opera

6〜8x
A high brightness value is recommended for watching a dim stage.

 

Object Lens Effective Diameter

If the object lens effective diameter is large, sharp images are obtained by the high light gathering power. However, the size also becomes larger as the effective diameter becomes larger, and it makes it difficult to carry them around.

Actual Field of View

It is recommended that you choose the kind with a wide actual field of view if you would like to use them for bird watching or sporting events.

Eye Relief

The longer the eye relief, the easier to view, because less stress is felt in the eye. If high-eyepoint design is employed, a sufficiently wide field of view is obtained.

Size

Choose the kind that suits your goal and observing style by considering the carrying method and observing location.

Fixed Magnification and Zooming Type

There are eyepiece lenses for binoculars and fieldscopes with fixed magnifications like 15x and 20x and zooming types with variable magnification like 8〜32x which can be controlled by a lever and etc. The zooming type allows you to change the magnification in accordance with what you are viewing and offers a broad range of uses. On the other hand, there is a disadvantage that the field of view obtained with high magnification can be narrow and dark.

Waterproof

The binoculars with waterproof design and fieldscopes are recommended for use in the seashore or in the environment where it is likely to get wet by the rain or snow.