Binoculars Explained : Design

Binoculars use image-erecting prisms to provide correctly oriented images. The two basic designs used in optical systems are the Porro Prism (off-set barrel) and the Roof Prism (straight barrel). Another modification of the Porro design is the Reverse Porro Prism, commonly used in compact binoculars to reduce overall size.

Porro Prisms
Porro Prism models are what most people picture when they think of a classic traditional binocular, with two offset barrels connected by a centre axis rod. Porro prisms tend to provide wide fields of view and crisp, sharp images. Porro prisms tend to be bulky and have been traditionally larger and heavier than equivalent roof prism binoculars. With recent modifications in optical design and production methods, modern Porro prism binoculars are much smaller and lighter in weight and may actually be lighter in weight than a roof prism of the same configuration. The Porro design is capable of delivering a wide field of view with excellent image sharpness. Also, they significantly cheaper than a comparable quality roof prism model.

Roof Prisms
Roof prisms are generally smaller and more streamlined in size and able to tolerate rough treatment better because of their compact optical design. Their complex prism configuration and the precise tolerances required during manufacture make top quality roof prism binoculars significantly more expensive than those of Porro prism design.

BAK 4 Prisms
The optical design of a particular binocular model is a compromise of several parameters to limit the amount of certain aberrations inherent in any optical system. The quality of glass used in the binocular lenses and prisms will determine the light transmittance, colour fidelity and clarity of the image. The size and design of the prisms will affect sharpness, with quality optical glass delivering clarity from edge to edge of the field of view (sometimes called a "flat field"). Binoculars which use prisms made of costly, high density glass (such as the BAK 4 type) will provide clear, circular exit pupils.

Collimation is the mechanical alignment of the optical elements in a binocular. Both right and left hand optical axis must have proper orientation and location within the binocular barrel and must be parallel to each other in a quality optical system. Hawke’s high quality mechanical construction ensures that the lenses and prism blocks maintain their correct alignment and provide years of comfortable viewing without headaches or eyestrain.

These are among the most important factors concerned with the optical quality and construction of a binocular. A poor optical instrument will not reproduce the image clearly and with frequent use may cause eye strain, headaches and fatigue. By investing in high quality Hawke binoculars, you will benefit with years of comfortable and enjoyable viewing.

Lens coatings
Ever looked at a lake with the sun shining on it? Did you notice the glare coming off the water? Well, that's what happens to binoculars that don't have coated lenses. Anti-reflection coatings reduce light loss and glare due to reflection of light at air-to-glass surfaces. Besides increasing the light transmission, coatings also provide sharper and higher contrast images and aid in detailed identification of low contrast subjects in limited available light. Multilayer anti-reflection coatings (multi-coatings) provide a significant increase in light transmission over single layer coatings and are used in all high quality optical systems.

There are 4 levels of coating:
Coated: A single layer on at least one lens.
Fully-Coated: A single layer on all air-to-glass surfaces.
Multi-Coated: Multiple layers on at least one lens.
Fully Multi-Coated: Multiple layers on all air-to-glass surfaces.