Charles holds a Master’s degree in Physics Engineering (optics and photonics specialization), has been teaching physics at school for almost 15 years and recently has star read more
Last updated: December 28, 2022
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A binocular is used for seeing distant objects, and if you use glasses, the focal length of your glasses is bound to interfere with that of the binocular. Due to this, there might be an added problem focusing on the object to be seen.
This article isn’t here to dwell on the problem but to show you how to use binoculars with glasses. But to better understand the steps that would need to be taken to adjust your binoculars to fit your eyesight defects, you would need to be familiar with terms such as eye relief.
Eye relief is the ideal distance of the eye from the eyepiece of binoculars. If the distance between the eye and the eyepiece is more than the eye relief of the binocular, the outer edges of the object being focused on may not be as clear as the rest of the object, and if the distance is less than the eye relief, you may not get a large enough image.
Types of binoculars
The knowledge most people possess about binoculars is limited to their ability to magnify. As such, it might seem surprising, but there’s more than one type of binocular, and each type has situations that they are more suitable to than the others
Trusted SourceBinoculars: Taking the Long View - The Washington PostMillions of bird-watchers, hikers, hunters, boaters and spectators find decent binoculars indispensable, paying prices ranging from less than $20 to more than $1,500 a pair.
Based on their general design and compactness, the types of binoculars are:
Roof prism – Binoculars that possess a roof prism utilize lenses and prisms that have been designed to sit right behind each other. This design makes for compact binoculars, but one of its real advantages comes in the form of better protection from dust and water. This better protection is because the binoculars with roof prisms can be focused by moving the lenses rather than the eyepiece. This means that there’s no opportunity for air to get in and consequently more protection from dust and water.
Porro prism – With this type of binoculars, the lens and eyepiece are not aligned as in the roof prism binoculars, but rather images are transported via an N-shaped bend. The need for the bend makes the housing of the binocular wider. The focus of the Porro prism can be adjusted by moving the eyepiece, and this could let in water and dust, but the binocular has a big advantage over other types as it provides better depth perception.
Monoculars – a monocular is a tool with only one lens and eyepiece. It is the most compact of all types of binoculars and can only be used through one eye. This always leaves the other eye free to roam and observe the environment. However, the disadvantage it has compared to the other binoculars is that you get less perception of depth when using it.
This is not the only classification used in differentiating between binoculars. They can also be classified based on how their lenses focus. According to this, there exist two types of binoculars, and they are:
Central focusing – this type of binocular has a central focus knob that is used to focus on the object to be viewed. It is much preferable for users with a regular need for binoculars because it eliminates the need to focus the binoculars for each eye individually.
Individual focus – This type of binocular is more suitable for astronomical viewing, and it allows for the user to focus separately for both eyes.
Based on these classifications, binoculars might vary in the functions they are most appropriate for. A binocular more suitable for close observation, such as the Celestron Nature DX 8×32, might not be suitable for astronomical observations.
Tips for eyeglass wearers
It is to be assumed that wearing glasses while using binoculars would be problematic, but whether or not a problem exists, the solution to the problem can only be figured out after you have identified what type of lenses are present in the eyeglasses you or the user is using.
The lens is selected based on the particular eye defect to be corrected.
If the user of the binoculars also uses eyeglasses, the following tips should be taken note of:
Using eyeglasses with binoculars would depend on the type of eye defect and the correction that is required to guarantee normal vision. Having said this, it is common to not require glasses when using binoculars, except you suffer from astigmatism, in which case you would need to use your glasses even with a binocular.
Farsightedness and nearsightedness are visual issues that would not require glasses while using binoculars. This is because the focusing of the lenses of the binoculars should correct whatever visual problems exist.
Binoculars alone cannot solve the visual problems of people with astigmatism as the lenses in a binocular allow for the manipulation and adjustment of the image distance but cannot correct spherical vision errors.
Binoculars adjustment guide
As earlier implied, certain features and factors in the use of a binocular have to be understood to adjust it successfully. One of such is the eye relief that has been defined earlier, but others are magnification, objective, diopter adjustment, focusing knob, eyecups, inter-pupillary distance, and how to avoid “vignetting” while using a binocular.
Eyecups or eye shields are usually designed to extend along the sides of the face to block out the glare of light, wind, dust, or any other distractions. They are usually made from rubber and may be detachable or retractable, depending on the design of the binoculars. If you are using a binocular with eyeglasses, fold or retract the eye shields to give the widest possible view.
Magnification can be defined as the number of times an image is magnified or made to seem closer to the eye of the user or viewer.
Objective refers to the diameter of the front lenses of a binocular. A larger diameter or objective gives a clearer image and is more useful in situations of dim light because light rays are better refracted through it. Having larger lenses would, however, make the binoculars heavier, as is experienced in many 10×42mm binoculars. A fantastic example of a binocular with a bigger lens is the Vortex Diamondback HD 10×42 Binoculars.
Diopter adjustment helps to cope with the natural difference between the two eyes and can be achieved via a knob located in the center of the binocular between both lenses.
The focusing knob is used to adjust the focus of a binocular to provide a clearer, sharper image. To achieve this, all you have to do is turn the knob until the image is perfect for you.
Vignetting is a blacking out of the image and can occur as a result of the effect of light rays on the peripheral vision of the user. It can also come as a result of an improper adjustment of the focus or diopter.
Inter-pupillary distance is the distance between the centers of both eyes. This distance varies from person to person and is measured in millimeters, just like eye relief. This can be adjusted by moving the tubes of the binocular upward or downward until the fields of vision of the right and left lenses align to form a perfect circle.
Which eye relief is suitable for eyeglasses wearers?
Because of the nature of the eye relief, the use of glasses is bound to mess with the setting.
A person using glasses would be focusing their images at a different distance from the eyepiece compared to an individual with perfect vision.
It is to remove this difference that individuals with near or farsightedness are advised not to use glasses while using binoculars. This is because their visual disorder can be corrected by adjusting the focus on the binocular.
However, the eye relief that provides maximum magnification and optimum comfort for viewing might still vary, and that’s why the best binoculars offer an eye relief range of 5-23 mm.
To set for the practically shorter distance between the eyepoint of eyeglass wearers and the eyepiece of the binoculars, adjustments are made to the eye relief, with experts tending to suggest a distance of 14-16 mm. This recommended eye relief is generally considered more suitable because it results in lesser strain or eye fatigue when focusing on objects.
Eyeglasses are useful for individuals with eye defects when they are living their everyday lives. But if they find themselves bird watching or performing any other task that requires the use of binoculars (such as spying), it becomes a hindrance.
While it might not be important to learn how to use binoculars with glasses because most visual disorders do not require such knowledge, astigmatism is one of those that do. Other than that, many users of glasses just feel more comfortable using their specs, and this makes this article applicable to them also.
Now that you know the major types of binoculars and the adjustments that can be made to accommodate for your use of eyeglasses, there should be nothing else stopping you from bird watching (or spying) or whichever outdoor activity interests you.
Binoculars: Taking the Long View - The Washington Post
Millions of bird-watchers, hikers, hunters, boaters and spectators find decent binoculars indispensable, paying prices ranging from less than $20 to more than $1,500 a pair.