Monocular
A compact refracting telescope using prisms for an erect image.
A monocular is a compact refracting telescope that magnifies distant objects. It uses an optical prism to keep the image upright, unlike many telescopic sights that rely on relay lenses. Because binoculars are essentially two monoculars joined together, a monocular typically weighs and costs less than half of a comparable pair, making it more portable. However, a monocular only provides a two-dimensional view, whereas binoculars deliver stereopsis and depth perception by combining two slightly different images from each eye.
Monoculars are ideal when three-dimensional vision is unnecessary or when compactness and low weight matter, such as on a hike. They are also useful for people who struggle with binoculars due to significant differences in eyesight between eyes, such as from strabismus, anisometropia, astigmatism, or unilateral visual impairments like amblyopia, cataract, or corneal ulceration.
Conventional refracting telescopes with relay lenses have a long, straight optical path. Monoculars use Porro or roof prisms to fold this path, making the device much shorter and more compact. That said, monoculars generally have lower magnification than telescopes of the same objective size and rarely offer variable magnification.
Visually impaired individuals may use monoculars to see objects at distances that people with normal vision can manage unaided, such as reading a chalkboard or projection screen. Other uses include natural history, hunting, marine activities, and military applications. Compact monoculars are also common in art galleries and museums for closer inspection of exhibits.
When high magnification, brightness, and resolution are needed, a larger instrument like a telescope—often tripod-mounted—is preferred. For less demanding tasks, a small pocket-sized monocular suffices. While binoculars are widely available, monoculars have a more limited selection, especially at the top quality level, with some renowned optical manufacturers not offering them at all. Most monoculars today are made in Japan, China, Russia, and Germany, with China offering the most variety. Prices range from under £10 for budget models to over £300 for high-end designs (as of February 2016).
Monoculars are defined by two parameters: magnification and objective lens diameter, expressed as, for example, 8×30 (8 times magnification, 30 mm objective lens).
- Magnification range
- 4× to 10× (most common); specialized units outside these limits available
- Objective lens diameter range
- 20mm to 42mm
- Most common magnification
- 8×
- Exit pupil definition
- objective lens diameter divided by magnification, expressed in mm
- Typical price range
- under £10 to over £300 (as at February 2016)
- Common manufacturing countries
- Japan, China, Russia, Germany
Lore & Background
Monoculars normally use Porro or roof prisms to 'fold up' the optical path, making them much shorter and compact than conventional refracting telescopes that use relay lenses. They tend to have lower magnification factors than telescopes of the same objective size and typically lack variable magnification. Most popular monocular sizes mimic popular binoculars, such as 7×25, 8×20, 8×30, 8×42, and 10×42.
Monoculars are ideally suited to applications where three-dimensional perception is not needed, or where compactness and low weight are important, such as hiking. They are also preferred when difficulties occur using both eyes through binoculars due to significant eyesight variation or unilateral visual impairment. Visually impaired people may use monoculars to see objects at distances at which people with normal vision do not have difficulty, such as reading text on a chalkboard or projection screen.
Whereas there is a huge range of binoculars on the world market, monoculars are less widely available with limited choice in the top quality bracket, with some traditionally very high quality optical manufacturers not offering monoculars at all. Most monoculars are manufactured in Japan, China, Russia, and Germany, with China offering more product variety than most.
Reader's Guide
Monoculars serve as a portable and often less expensive alternative to binoculars, particularly valued where compactness and low weight are critical, such as hiking. They are also useful for individuals with eyesight variations or unilateral visual impairment who cannot comfortably use binoculars. Applications include natural history, hunting, marine, military, and viewing exhibits in art galleries and museums. The choice of magnification and objective lens diameter involves trade-offs: higher magnification narrows the field of view and reduces image brightness, making 8× or 10× popular compromises. Exit pupil size, twilight factor, transmittance, and field of view are key design parameters. Eye relief is important for spectacle wearers, with at least 15mm desirable. While monoculars lack the depth perception of binoculars, they offer the same field of view for a given specification. The distinction between a monocular and a telescope is debatable, but telescopes are normally used for high magnifications (>20×) with larger objective lenses and typically require a tripod.
Did You Know?
- Monoculars typically have less than half the volume and weight of binoculars with similar optical properties.
- Monoculars use Porro or roof prisms to fold the optical path, making them compact.
- The most common and popular magnification for monoculars is 8×.
- Monoculars are less widely available than binoculars, with limited choice in the top quality bracket.
Frequently Asked Questions
Who is Monocular?
Monocular is a compact refracting telescope that employs an optical prism to deliver an upright image of distant objects. Rather than relying on the relay-lens systems found in many telescopic sights, it achieves the erect view through prism optics.
What are Monocular's powers and role?
Monocular typically operates in a 4× to 10× magnification range, with 8× being the most common setting. Its role is to give users a lightweight, affordable magnified view in situations where three-dimensional depth perception is not needed.
Why is Monocular important?
Because a pair of binoculars is essentially two monoculars joined together, a single monocular weighs and costs less than half of a comparable pair. That makes it the natural choice for portability and for users who want magnification without the bulk or expense of a full binocular set.
What equipment does Monocular carry?
Monocular's objective lens spans 20 mm to 42 mm in diameter, and its exit pupil is found by dividing that diameter by the magnification. Units are produced in Japan, China, Russia, and Germany, with retail prices ranging from under £10 to over £300.
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