When shopping for optics, don’t forget to have a look at Vortex. They make a high quality product, sold for a price that most of us can afford. They also put out a booklet called “All About Optics”. I’m sure if you called them (800-426-0048) or e-mailed them ([email protected]) they can get you a copy. For those not so inclined, I’ll post a lot of their info here.

From their booklet:

How do binoculars work?

All binoculars, regardless of their size and shape, function in the same straightforward way:

1. Light comes to and moves through the objective lenses

2. Light then travels through the prisms (which correct the image orientation in all directions; up-down, left-right)

3. Finally, light moves through the eyepieces (which magnify the images) and then on to the user’s eyes.

What determines image quality?

1. Optical Glass – The quality of optical glass that is used in binoculars will make a difference in how bright, sharp, and colorful the view will be. Quality binoculars use dense optical glass that is painstakingly designed, shaped, and polished to eliminate flaws. The more sophisticated the glass and techniques employed in its design, the better the images.

2. Anti-reflection coatings – Binocular lenses are coated with anti-reflection coatings to eliminate internal reflections and light scattering, reduce glare and produce sharper images with more detail. The type of coatings and the number of coatings applied to the binocular lenses matter tremendously to how brilliant and crisp the view will be.

3. Exit pupil – The exit pupil is the beam of light that exits each eyepiece of the binocular and enters the users’ eyes. The larger the exit pupil, the brighter and more superior the image will appear, especially under low light conditions (when comparing optics of similar quality). The exit pupil is measured in millimeters, and is calculated by dividing the objective lens by the magnification. An 8×42 binocular, for example, has a 5.25mm exit pupil (42/8 = 5.25)

Binocular Design

Though they look different on the outside, on the inside binoculars can only be designed a few ways:

Galilean Design
Used almost exclusively in opera glasses, the Galilean design is very primitive and uses only lenses (no prisms)

Porro prism design

Named after their Italian optical designer, Porro prism binoculars are characterized by the objective lenses being spaced wider apart than the eyepieces. The design is reversed in compact binoculars, with the eyepieces spaced wider than the objectives.

Roof prism design
Named after the “roof-like” appearance of the prisms, the more modern Roof prism design features a more complicated design, resulting in the objectives and eyepieces being positioned in a slim, straight line.

Optics 102 will be the next installment, and will include “What do the numbers mean?

Meanwhile, stop by and visit the folks at Vortex