Lithuania

Binoculars

Basic knowledge

Basic knowledge for better choices

The fact that binoculars can be used in a wide variety of situations means that each product has its own specialties. Therefore, it is important to have a basic knowledge of the product and to know for which purpose it is used.

[image] 8(Magnification)x42(Objective Diameter (mm))
Magnification

Magnification indicates how much larger an object appears compared to the naked eye when viewed through binoculars. For example, using 8x binoculars makes an object appear the same size as it would if viewed with the naked eye from 1/8th of the distance.

Objective Diameter (mm)

The lens located on the front side of the binoculars when you look through, is called the objective lens. The objective diameter represents the size of this lens.

Key Points for Selection

Higher magnification allows you to view objects from a greater distance, but it narrows the field of view and makes the image more susceptible to hand shaking. Additionally, larger objective lenses have better light-gathering capabilities, resulting in brighter images, but they also increase the size and weight of the binoculars. Understanding these pros and cons is essential when choosing binoculars.

Types of Binoculars

There isn't just one way to categorize binoculars. Understanding the distinct features of each type makes it easier to choose a product that meets your specific needs.

Prism

In order to achieve high magnification and a wide field of view, binoculars employ an optical system (Keplerian design) that uses convex lenses on both the objective lens and the eyepiece lens. This results in an upside-down image, which is then corrected using prisms. There are two types of prisms used for this purpose: Porro prisms and Dach prisms.

[image] Porro Prisms
[image] Dach Prisms
Characteristics of each type of Fujinon binoculars

Porro Prisms

[photo] Mariner / FMT/MT / LB150

Dach Prisms

[photo] Techno-Stabi / Hyper Clartity / Stabiscope
CF and IF Mechanisms

The CF (Center Focus) mechanism adjusts the central focus knob of the binoculars to simultaneously focus both eyes. On the other hand, the IF (Individual Focus) mechanism adjusts the focus separately with dedicated focus knobs for each eye. Since achieving waterproofing is somewhat challenging with the CF mechanism, the IF mechanism is used for waterproofing in Porro prism binoculars. IF mechanism is well-accepted for applications such as marine and astronomical observations where frequent focusing is not required. However, it is rare for IF mechanism to be used in other scenarios due to the time-consuming nature of individual focus adjustment.

Characteristics of each type of Fujinon binoculars

CF

[photo] Techno-Stabi / Hyper Clartity

IF

[photo] Mariner / FMT/MT / LB150 / Stabiscope
FUJINON's Unique Vibration Control Mechanism

FUJINON binoculars incorporate a vibration control mechanism that ensures the binoculars' vibrations do not affect the prism's alignment by employing a gimbal system for the roof prism. This mechanism provides a significantly wider range of stabilization compared to lens shift-based vibration control in digital cameras or other brands' image stabilized binoculars.

[image] A breakdown of the different parts that make up electronic gyro stabilizing system of the Techno-Stabi Series

Principle of Image Stabilization

Techno-Stabi System

This system detects binocular vibrations electrically using gyro sensors and drives the gimbal through actuators to maintain a stable alignment. It is lightweight, offers excellent noise reduction, and can be implemented at a relatively affordable cost.

Stabiscope System

This system attaches a high-speed rotating flywheel to the gimbal to maintain a stable alignment through inertia. It provides exceptionally stable vibration reduction, although the motor and flywheel are relatively heavy and produce some noise. It is also comparatively expensive but offers superior stabilization performance.

Characteristics of each type of Fujinon binoculars

Techno-Stabi System

[photo] TS-X 1440 / TS12x28 / TS16x28

Stabiscope System

[photo] S1240 S1640

Knowledge about Catalog Specifications

Magnification

Explanation provided at the beginning of this page, so omitted.

Objective Diameter

Explanation provided at the beginning of this page, so omitted.

Field of View

It represents the range visible through binoculars in terms of the angle seen with the naked eye.

Eye Relief

If the eye relief is short, you need to bring your eyes closer to the eyepiece lens to see the entire field of view. If you wear glasses, it is desirable to have a long eye relief (14mm or more).

Minimum Focus Distance

The shortest distance at which binoculars can focus. A smaller value is effective for observing flowers, insects, museum exhibits, and artwork.

Dioptric Adjustment Range

Indicates how much it can correct the difference in visual acuity between the left and right eyes.

Adjustment Range for Interpupillary Distance

Since the width of the eyes varies greatly among individuals, a wider adjustment range is desirable. Westerners tend to have a narrower interpupillary distance, while Asians tend to have a wider interpupillary distance.

M: Magnification, D: Objective Diameter, F: Field of View

Specifications Reflecting Brightness
Exit Pupil = D/M

Most commonly used indicator of brightness worldwide

Relative Brightness = (D/M)2

Less frequently used as an indicator

Twilight Factor = (D*M)1/2

Mainly used in Europe

Note that the above specifications do not consider the actual transmittance and reflectance of the lenses and prisms. Therefore, it is important to note that with the same M and D values, the brightness value will be the same for both high-end and entry-level binoculars.

Specifications Field of View
Field of View at 1000m = 2* 1000* tan(F/2)

Some regions may express it in yards instead of meters

Apparent Field of View = 2* arctan(M* tan(F/2)) 

See the diagram below

* Those with an apparent field of view of 60 degrees or more are referred to as 'Wide Field'.