Monocular

The volume and weight of a monocular are typically less than half of a pair of binoculars with similar optical properties, making it more portable and also less expensive.

Monoculars are ideally suited to those applications where three-dimensional perception is not needed, or where compactness and low weight are important (e.g. hiking).

Conventional refracting telescopes that use relay lenses have a straight optical path that is relatively long; as a result, monoculars normally use Porro or roof prisms to "fold up" the optical path, which makes it much shorter and compact (see the entry on binoculars for details).

Applications for viewing more distant objects include natural history, hunting, marine and military.

Contemporary monoculars are typically compact and most normally within a range of 4× magnification to 10×, although specialized units outside these limits are available.

Variable magnification or zoom is sometimes provided, but has drawbacks and is not normally found on the top quality monoculars.

This represents a usable magnification in many circumstances and is reasonably easy to hold steady without a tripod or monopod.

At this magnification, the field of view is relatively wide, making it easier to locate and follow distant objects.

Most serious users will eventually come to realize why 8× or 10× are so popular, as they represent possibly the best compromise and are the magnifications most commonly adopted in the very highest quality field monoculars (and binoculars).

Much of the basic design considerations and related parameters are the same as for binoculars, and are covered in that entry, but some expanded comments have been added where appropriate: Exit pupil is defined as the diameter of the objective lens divided by the magnification and expressed in mm.

The classic 7×50 marine binocular or monocular is ideally suited to low light conditions with its relatively large exit pupil diameter of 7.1mm and a realistic magnification which is practical on a moving boat.

The following chart shows the FOV/magnification relationship based on best-in-class data, taken both from tests and manufacturers' specifications.

Eye relief is a particularly important (but often overlooked) parameter for spectacle wearers, if the full field of view is to be visible.

The small ring near the eyepiece also usually needs two hands to operate, and, in some designs, can interfere with the twist-up eye cup.

The small degree of twist gives a very fast focus, but can be overly sensitive, and, in some designs, be too stiff to use with one hand.

A focusing wheel tends not to be used on top quality monoculars (with the exception of the Bushnell 10×42HD Legend), but is particularly popular on budget offerings from China.

[7] This mechanism provides very quick focusing while retaining compactness, but can be stiff and overly sensitive to use, and again, ideally needs two hands.

It provides a one-handed focus mechanism in a relatively large toggle, making it quick and easy to operate "in the field" with gloves, but can be over-sensitive and difficult to fine tune.

The knurled ring around the objective lens appears to be a unique feature of the Minox 8×25 Macroscope and claims to provide quick focusing.