Understanding Binoculars, Brightness, Prisms, Contrast, Resolution

Understanding Binoculars - Lens Coatings, Focusing

Understanding Binoculars - Exit Pupil,  Field of View, Eye Relief, Near Focus

Understanding Binoculars - Magnification, Objective Diameter

The level of brightness of an image when looking through binoculars is dependent of several factors such as the binoculars ability to gather light (based on the size of the objective lens), the level of magnification (lower magnification binoculars tend to deliver brighter images) and the size of the exit pupil (large exit pupils will help improve the brightness of an image).

Other factors that will have an influence on how bright and image will appear is lens quality, the type of lens coating (good quality binoculars should have fully multi-coated lenses) and the type of prisms used.

The level of brightness when observing objects with binoculars will also have an impact on the clarity of colour, the brighter the image the greater the colour differentiation is likely to be.

There are two basic designs of prisms, roof prisms or porro prisms. Lightweight, compact binoculars are generally fitted with roof prisms which are lighter in weight and more portable.

The purpose of prisms in binoculars is to invert the image and the quality of the prism will have a distinct impact on the clarity of the image. Higher grade binoculars will come with multi-coated prisms or the Canon 18x50 IS Binoculars, for example, come with Vari-Angle Prism which will constantly adjust for even the slightest movement in the binoculars.  Nikon use phase-corrected-coated prisms for high resolution.

Prisms are denoted as being either BAK-4 or BK7. BAK-4 prisms are considered to be the best quality being of finer glass which is of a higher density thereby almost eliminating and internal light scattering. Better quality prisms produce sharper more well defined images.

When we talk about contrast we are referring to the binoculars ability to differentiate between dark and brighter images and between objects and their background. When you are trying to view distant objects with your binoculars, and you want to see the finer detail of the image, the level of contrast your binoculars provides is important. Contrast is impacted by (among other influencing factors):

• The quality of the lenses
• Resolution
• The quality of the eyepiece
• The quality of the prisms

Resolution  is a measurement of a binoculars ability to enable you to see the fine detail of the image you are viewing and is directly related to the size of the objective lenses. As a general rule of thumb the larger the objective lenses the greater the detail you will be able to see although other factors play a part such as:

• The quality of the lenses
• The type of lens coating
• Correct optical alignment

Bird Watching Binoculars / Astronomy Binoculars / Compact Binoculars

Understanding Binoculars cont.........