A monocular is an alternative to a pair of binoculars, used to view distant objects.
Monoculars, sometimes known as pocket telescopes, are optical devices used to view objects in the distance. They are typically handheld like binoculars but have only one tube, making them miniature telescopes. The advantages of monoculars over both telescopes and binoculars include their portability, especially some small monoculars which are only the size of a pen. The disadvantages are that monoculars are not designed for continuous viewing, so they are not as comfortable to use as binoculars, nor do they offer the same optical quality.
Like binoculars, monoculars use lenses and prisms to transmit light and magnify objects. The arrangement of prisms affects the length of the monocular. Unlike binoculars, they do not provide three dimensional viewing with depth impression. The view is two dimensional and flat. This does not affect their application for many uses but does make them unsuitable for others.
Monoculars may be used by both normal sighted and visually impaired people to read distant signs, view fixed distant objects and for similar uses. Many people view them as a backup to binoculars and carry them in situations where binoculars are impractical. Monoculars may also be used as magnifying glasses up close. They are not generally used for continuous use as in theatres or at sporting events. Advanced monoculars may be used in professional environments, such as marine and military environments. Larger and high resolution monoculars may require the use of a tripod.
Choosing a Used Monocular
Which monocular is most appropriate depends upon several integral features of the monocular, including the magnification, objective lens size, field of view, eye relief, close focus, lens coatings, and special features such as being waterproof.
The magnification is the extent to which objects are enlarged or appear closer. There are two sides to magnification, and higher magnifications are not always best. The advantage with higher magnification, of course, is that objects appear closer and more detail can be made out.
However, higher magnification has its drawbacks. Most important this entails a narrower field of view, so objects cannot be spotted as easily, and scanning is more difficult. It is also harder to hold an object in view and steady. With higher magnifications, objects have a tendency to skip out of view, and it can be hard to relocate them.
For this reason, magnifications which strike a good balance between resolution and practicality are typically preferred. This applies especially to lightweight handheld monoculars. If a tripod is used, it is easier to steady the monocular and to keep distant objects in view once located.
Magnifications of 5x or 6x are typically recommended, which is a slightly lower magnification than most standard binoculars. This is because monoculars are used mostly to view objects briefly rather than continuously and because binoculars are easier to steady. A 5x or 6x monocular will typically be easy to use, but an 8x or 10x will be more difficult. Anything larger will very likely need a tripod.
Zoom monoculars of varying magnification ranges are also available. While these may offer exceptional convenience, bear in mind that due to their more complex components, they are typically less durable.
As with binoculars, the magnification is usually written on the monocular. It is written first, followed by the objective lens size. For example, a 5x10 monocular has a magnification of 5x.
Objective Lens Size
The objective lens size is the actual diameter of the lens at the end of the monocular. This is the point where light enters the monocular and therefore has a large impact on image quality, with more light enabling brighter and clearer images to be transmitted to the viewer.
However, as with high magnification, large objective lenses have their disadvantages. The objective lens size is a limiting factor in how small the monocular can be. Larger-sized objective lenses mean larger, less lightweight and less portable, monoculars. Because monoculars are smaller than binoculars, this issue is often not as important.
While a large objective lens may not be necessary for many purposes, especially for viewing in normal light conditions, it is more important in low light. This is because it is more difficult for light to enter the monocular, so a larger lens is required for the same effect. For stargazing it is recommended to have a large objective lens of around 35 mm or more.
While objective lens size affects image quality, it is quite possible with intelligent design with regards to prism arrangement and with high quality optical components to produce clear, bright images with smaller monoculars.
The objective lens diameter is the number given after the magnification. It is measured in millimetres. For example, a 5x10 monocular has an objective lens diameter of 10 mm.
Field of View
The field of view is the area seen through the monocular. Field of view depends upon various factors, including magnification, objective lens size and prism arrangement. Monoculars with a higher magnification will have a smaller field of view, all other factors being equal. So will monoculars with larger objective lenses and monoculars with more complex prism arrangements designed to give a wide field of view.
However, larger objective lenses and more complex optical paths add size and weight, so the monocular is typically not as portable.
Eye relief is the furthest distance that the eye can be placed from the eyepiece without losing any of the field of view. It is measured in millimetres. This is an especially important point for people who wear glasses, in which case a monocular with eye relief of at least 14 mm is recommended.
Close focus is the shortest distance that a monocular can focus on. While monoculars are usually used to view distant objects, they can also be used to view very small objects at a close distance. For example, they could be used to view insects such as butterflies at short range without disturbing them.
Like binoculars, optical coatings are used on the lenses and prisms to encourage better light transmission and produce brighter images. Monoculars that are fully multi-coated, with multiple coatings throughout, have the best light transmission. Monoculars that are multi-coated, with multiple coatings in some areas, and fully coated, with a layer of coating throughout, are also worth checking out.
Look out for a waterproof monocular if it is to be used on water, for example while sailing or kayaking, or frequently in very wet or humid conditions. Monoculars that can be used with a tripod may also be useful, and some actually come with a tripod as part of a kit.
Used and Vintage Monoculars
When buying a used monocular, read the product description carefully for any signs of damage, such as scratches to the lenses or dents to the body. Items should be fully functional unless stated otherwise. Older monoculars may become misaligned, especially zoom binoculars, which have more complex mechanics. Monoculars may come with accessories, such as cases and tripods. There are some very nice vintage and antique monoculars available if a certain style of monocular is desired. Always check seller feedback and reviews, and compare the price against other similar items.
Find a Monocular on eBay
To find a monocular on eBay, go to the home page and scroll over the Electronics tab, selecting the Cameras & Photography page. Then scroll down the tabs and select Telescopes & Binoculars. Select Binoculars & Monoculars followed by Monoculars. Scroll down and, under the heading Condition, select Used. These items should be fully functional. There are options to select a particular brand and price range as well as maximum magnification and other features.
Alternatively, use the search bar at the top of the page. Type in terms such as “used monocular”, “used monocular 5x” or “antique monocular” and press Search. The listings can then be refined using the above or other criteria if required.
Monoculars are optical devices, consisting of one tube, used to view distant objects. Advantages over binoculars and telescopes include portability, with some monoculars being extremely small. Disadvantages include their lack of depth and lack of comfort for continuous viewing. Factors to consider when purchasing a monocular include magnification, objective lens size, field of view, eye relief, and special features. 5x and 6x are generally considered good magnifications for portable monoculars. Zoom monoculars are convenient but often less durable. Objective lens size can be an indication of image quality, with larger lenses typically producing brighter images. Field of view depends upon magnification, objective lens size, and other factors such as the arrangement of prisms within the tube. Eye relief is the distance the eye can be placed without losing any field of view, and is especially important for those who wear glasses. Other considerations include special features such as waterproofing. Check the product description and seller feedback when buying a used monocular.