Glossary - Binoculars - Canon South & Southeast Asia

    Prism Types

    Prism-type binoculars are split into two categories - Porro and Roof types. As our binoculars are designed with resolution and brightness in mind, all Canon binoculars are constructed with Porro prism for its superior optical performance. It delivers a high level of sharpness, suppresses light loss, and focuses light directly to the eyepiece optics without any loss.

    Porro prism type

    Porro Prism Type

    Excellent optical performance

    Difficult to make into compact and lightweight version

    Roof prism type

    Roof Prism Type

    Easy to make into compact and lightweight version

    Cost tends to increase with optical performance improvisation

    Field of View

    field of view_1170x460

    Due to optical design and differences in construction, the area visible will differ even on binoculars with the same magnification. The area visible is called the ‘field of view’ and there are three expressions used in binoculars: real field of view, apparent field of view, and 1000 m field of view. In general, the wider the field of view, the easier it is to find objects, making binoculars more comfortable to use. In ISO standards and the new JIS standards for telescopes, an apparent field of view of 60 or more is called a wide field of view type, which is one of the criterias to choose binoculars.

    Real field of view
    [Unit: °]
    1000 m field of view
    [Unit: m]
    Apparent field of view
    [Unit: °]
    The area that can be seen without moving the binoculars. The area at 1,000 m ahead that can be seen without moving the binoculars. The field of view visible through binoculars that appears at the same size as when looking with the naked eye.


    Types of Image Stabilization

    Shift Method

    This construction moves a lens equipped with a vibration gyroscope mechanism vertically and horizontally in the correct direction to cancel shaking. In addition to deliver sharp images with minimal colour bleeding, it offers better power saving performance than VAP method. As the construction is simple, it offers the advantage of a better grip design.

    VAP Method

    When two glass elements are arranged in a bellows shape within the lens barrel and filled with liquid, it is called a “liquid prism”. The lens changes shape according to shaking, adapting to the direction of refraction to instantly stabilize the image. The left/right VAP units are connected and driven by a simple mechanism. This construction results in a compact size and precise conformity between the left/right optical axes, lessening the load on the drive actuator for reduced power consumption.

    Eye Relief

    Eye relief refers to the length where the image is visible without obstruction. Binoculars with a longer eye relief (high eyepoint) are easier to look through and causes less fatigue even after long period of use.

    When using the binoculars with glasses, we recommend to reverse the eyecups.