What are binoculars?

Binoculars are also called field glasses. It consists of 2- telescopes mounted side-by-side & aligned to point in the same direction, allowing the viewer to use both eyes when seeing far objects. Most of the binoculars are sized in such a way that, they can behold by using both hands, however, sizes vary widely from opera glasses to huge pedestal mounted military models.

Types of Binoculars

There are two main types of binoculars.

– Porro Prism Binoculars

– Roof Prism Binoculars

Porro Prism Binoculars

Porro prism binoculars are named after the famous Italian optician ‘Ignazio Porro’ who monopolize this image erecting system in the year 1854, which was later on refined by makers like the ‘Carl Zeiss’ company in the year 1890. This type of binoculars uses a pair of Porro prisms in a Z-shaped configuration to erect the image. This results in binoculars that are wide, with objective lenses that are well separated & offset from the eyepieces, providing a better sensation of depth. Porro type prism designs have the added benefit of folding the optical path so that the physical length of the binoculars is fewer than the focal length of the objective.

Advantages

– Porro prisms have objective lenses spaced larger than roof prisms, & so can produce a slightly fine stereoscopic image than the roof prism design.

– It’s cheaper to make high-quality Porro prisms than of roof prisms so they tend to be cheaper to buy.

– Basic optical quality is much greater to roof prism bino.

– All internal surfaces are totally reflective, so there is less chance of light loss due to the prism system.

Disadvantages

– They are less compact design than roof prism binoculars.

– Also, more moving parts, more to go wrong & harder to make fully water & dust-proof.

– Struggles in tough weather.

Roof Prism Binoculars

Binoculars using roof prisms appeared in the year 1870, design by ‘Achille Victor Emile Daubresse’. In the year 1897 ‘Moritz Hensoldt’ started marketing roof prism binoculars. Most roof prism binoculars use either the ‘Abbe-Koenig’ prism or the ‘Schmidt-Pechan’ prism which was invented in the year 1899 designs to erect the image & fold the optical path. Basically, they have objective lenses that are approximately in line with the eyepieces.

There are 2 prisms in a roof prism assembly. The front prism has one surface that has no internal reflective features. To overcome this, a special coating is applied like a mirror coating in order to raise its reflectivity to limit light loss. While the second prism has a point where the light reverse off an edge which requires the maker to use advanced technology to cut down chromatic aberrations such as color fringing & double vision. To fix this, mostly a phase-corrected coating is used to maintain light-waves in-phase.

In Roof Prism binoculars, light enters the objective bell through to the  2-prisms in the roof assembly. The light path leads through a course of 6-reflections to produce a crosswise & vertically erect image, the light then exits the binocular through the eyepiece in the same aligned line that it entered the objective bell. All of this happens in a very straight line, which explains why you can have a more compact, streamlined, & weatherproof binocular.

Advantages

– Compact in design.

– Lighter in weight.

– Suitable for tough conditions.

– Less internal parts than Porro prism design means less to go wrong & easier to make dust & waterproof.

Disadvantages

– Quality of image in roof-prism binoculars can suffer slightly because of the aligned prisms.

– This requires advanced technology to manufacture.

– The best & high-quality roof prism binos will be pricey because of the technology & the coatings.

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