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. |
The
difference between BAK4 and BK-7 prisms BAK4 prisms (barium crown glass) are the highest quality available. BK-7 prisms (borosilicate glass) are also good quality, but brightness falls off slightly at the edge of the field compared to BAK4. |
| 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. |
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 binoculars, you will benefit with years of comfortable and enjoyable viewing. |
| 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. |