Frequently Asked Questions (FAQs) on Binoculars
What is the 'Optical Quality' of binoculars?
The optical elements of the binocular are the coated to reduce internal light loss and glare, which in turn ensures even light transmission, resulting in greater image sharpness and contract. Choosing a binocular with good lens coating will translate to greater satisfaction with the product you ultimately select. Lens coatings range in quality as follows: coated - fully coated - multicoated - fully multicoated. Coated lenses are the lowest quality. Fully coated lenses are quite economical and can work well for you, depending on your needs. Multicoated or fully multicoated lenses are both very good choices. Fully multicoated lenses give the best light transmission and brightest images, and therefore the most desirable.
Optical alignment requires a durable, rigid housing to ensure precise alignment of lenses, prisms and eyepieces. If the alignment is the slightest bit off, the result will be eyestrain and headaches. If alignment is off by a large amount, double or crossed vision will occur. Prism design and the quality of glass used determines the prism quality. A binocular with a high quality BaK-4 prism will deliver crisp colours and clear, round exit pupils. A lower quality prism delivers dull colours and exit pupil with squared off edges. Lens quality determines the quality of colour, brightness, contrast and sharpness. Extra-low dispersion glass (ED glass) or fluorite glass are used to proved sharp, brilliant images. To improve brightness and contrast while reducing glare and light loss, anti-reflective coatings are used. For the best detail and contrast, choose a fully multi-coated optic.
Isn't Higher Power better in a binocular?
Not necessarily! Many of our customers cannot hold a higher power binocular steady which makes the image jumpy or blurry. Higher power binoculars are generally less bright, have a narrower field of view and can seem less clear because any particulates in the atmosphere (heat, moisture, dust) are also magnified to a greater degree. Ten power (10x) is often the magnification at which you may see too much jumpiness.
What is 'Objective Lenses' of Binoculars?
The main (objective) lenses of a binocular serve to collect light, thereby enabling the high resolution observation of distant objects. In a quality binocular each objective lens typically is manufactured of two separate glass elements, the so-call crown and flint elements. The refractive specifications of these elements permit the objective lens to image objects free of false colours.
A good forty to forty two mm objective is just right for an ordinary binocular. This objective is also preferred for hunting during legal hours. If you prefer a more detailed and visible shot, the larger 50mm to 56mm lens is advisable for hunting during nighttimes. Though a bit heavy and expensive than the conventional 40mm lens, they are still great and functional for your hunting needs. If you are a light traveller, hunting binoculars having 30mm to 32mm objectives are good options. Portability and performance wise, these are good options. A 20mm to 25mm objective is also available if you really want to travel lightly.
What is 'Prisms' of Binoculars?
Since the objective lenses form images that are both upside-down and reversed left-for-right, prisms are required to invent the primary image. Most commonly, binoculars utilize either Porro prisms or roof prisms for this purpose. Porro prisms give binoculars their familiar zig-zag profile, while roof prisms permit a straight-line design. Either type of prism could be designed BK-7 or BAK-4. Both are economical and highly effective designs. The finer glass in the BAK-4 design is of high density and virtually eliminates internal light scattering, producing sharp and defined images.
What is 'Eyepieces' of Binoculars?
The larger the aperture, the higher the practical magnification limit. Since more light is collected and brought to focus by a larger aperture telescope, fainter objects can be seen with it than with smaller apertures. Under good seeing conditions when air is not turbulent, a larger aperture objective gives higher resolution, letting you see finer details.
What is 'Specifications' of Binoculars?
Binoculars are classified as, for example, 10x25mm read 'ten by twenty-five millimetres.' In this case the binocular is of ten-power ('10x') and includes objective lenses of 25mm (about 1') diameter. Other binoculars might range from a tiny 3x18mm to giant battleship binoculars that are 40 x 100mm. The 'WA' designation after a binocular specification, such as 10 x 25mm WA, refers to the wide-angle design of the binoculars eyepieces; wide-angle eyepieces can increase a binoculars visual field of view by as much as 60%.
What is 'Magnification' of Binoculars?
Magnification, or power, is perhaps the most misunderstood term in binocular optics. While higher powers can be useful, power by itself does not increase the level of observable detail; image resolution is a function of objective lens diameter and type of prism, not of binoculars power. Higher powers result in images that are less bright and in a binoculars that is more difficult to hold steady in user hands. Power of 7x to 16x are by far the most popular among regular binocular users. Binoculars with magnification above 20x are generally not recommended for use without tripod.
What is 'Field of View' of Binoculars?
A binoculars field of view is measured in degrees of arc or as field-width (in feet) at 1000 yards distance. Example: The Saxon 8x42 WP waterproof roof prism binocular has a field of view 367 ft. wide for an object 1000 yards distance from the observer, yielding a field of view specification of 367 ft. at 1000 yards. Depending somewhat on the observer's intended applications; wide-angle binoculars are generally well worth the relatively modest additional cost involved.
What is 'Eye Relief' of Binoculars?
Eye relief, also known as exit pupil distance, is maximum distance between the eye and the eye lens of the eyepiece to see the eyepiece's field stop. (The field stop is the baffle at the image plane that produces the field edge.) Adequate eye relief is a very important factor for comfortable viewing. Eye relief generally decreases as power increases. Low eye relief (less than 10mm) requires you to get very close to the eyepieces, while higher eye relief (greater than 15mm) allows more distance. Eyeglass wearers need a higher amount of eye relief to allow room for their eyeglasses, however- many eyeglass wearers are surprised to find that they don't need their glasses when viewing with binoculars. For many eyeglass wearers, the binocular can replace their eyeglasses.
Binoculars users who wear eye glasses for near- or far-sightedness may remove their glasses while observing; the binoculars can fully correct for these eye defects. Observers who suffer from astigmatism, however, may need to wear their glasses to maintain sharp imaging through the binocular. In this latter case choosing a binocular with longer eye relief (15mm or longer) with enable easier binocular observing with eyeglasses.
What is 'Lens Coating' of Binoculars?
An uncoated optical glass lens or prism reflects about 10% of the light incident on one of its surfaces, allowing only about 90% of the light to pass through. Standard coatings of magnesium fluoride applied to the lens and prism surfaces reduce the level of reflected light to about 4%, and with substantially reduced ghost images of bright objects. More sophisticated multi-coatings further reduce reflected light and can result in total light transmission through a lens or prism of 99% or more. Some models are multi-coated with perhaps the most advanced multi-coatings available, permitting 99+% light transmission and extremely high image contrast. In addition, some binoculars come with ruby coated objective lenses which protect user's eyes from UV emission.
Coated (C) - One or more surfaces are coated.
Fully-Coated (FC) - All air-to-glass surfaces are coated but plastic lenses may not be.
Multi-Coated (MC) - One or more surfaces are coated.
Fully Multi-Coated (FMC) - All air-to-glass surfaces are coated.
Coatings prevent reflection and scattering of light- which minimizes light loss and offers better image contrast. An uncoated glass surface can lose up to 5% of light transmission due to reflection and scattering. A single layer of anti-reflection coating can reduce loss to about 1.5%. Multiple layers of different anti-reflection coatings can further reduce loss to as low as 0.25%. Multi-coating therefore, provides a higher level of light transmission and image contrast.
What is the difference between multi-coated and fully multi-coated optics?
Most quality binoculars have multi-coated objectives and oculars, but it's also important that all internal air-to-glass surfaces are coated (fully coated) or multi-coated (fully multi-coated) as well. Only the highest quality binoculars are multi-coated on all glass-to-air surfaces (fully multi-coated). This costs more, but allows the highest level of light transmission.
Coatings are one of the most important factors in determining image brightness. Many budget binoculars have several uncoated surfaces – this is unacceptable, since each uncoated glass surface reflects about 4-5% of incoming light. In the worst binoculars, only about half of the light entering the instrument actually makes it to your eyes. The result is a dim, washed-out image and a poor observing experience. Such binoculars are normally advertised as having 'Coated Optics', and are unacceptable for all but the least demanding uses. The simplest form of coating is a single thin layer of Magnesium Fluoride. This is a good coating, but Magnesium Fluoride coatings lose about 1.5% of light per surface. That may not sound like much, but keep in mind that most binoculars have 14 to 20 optical surfaces that the light must pass through before reaching your eye. That can translate to some serious light loss - in excess of 25% - for a magnesium fluoride-coated binocular. Binoculars with magnesium fluoride coatings on every surface are called 'Fully Coated' binoculars, and are acceptable for some undemanding uses, but generally not for astronomy. The next coating level is binoculars with 'Multi-Coated' optics – this generally means that at least the inside surface of the objective lenses and one or more surfaces of the eyepiece lenses feature coatings made of multiple very thin layers (hence the term 'multi-coated'). A properly applied multi-coating can appear any colour but will normally look greenish-purple, and will transmit between 99% and 99.7% of the light passing through each surface. What this boils down to is that, depending on the number of multi-coated surfaces, a 'multi-coated' binocular can have various levels of improvement in light transmission and contrast over a fully-coated binocular. If only a few surfaces are multi-coated, the improvement will be negligible, but if the objectives and eyepieces are multi-coated and only the prisms retain magnesium fluoride coatings, the improvement can be significant. Unfortunately, there are no hard-and-fast rules for determining what constitutes a 'multi-coated' binocular, so it’s possible for a manufacturer to sell a binocular that has multi-coatings on only one or two surface, and no coatings on all the others. In this case, you’d be better off with a standard 'fully coated' binocular. Beware of inexpensive binoculars where the multi-coating is too thickly applied, as this can actually hurt performance over a Magnesium Fluoride-coated binocular. Also avoid so-called 'Ruby-coated' binoculars like the plague. The best binoculars utilize multi-coatings on every air-to-glass surface (including the long faces of the prisms) and are called 'Fully Multi-Coated' or 'FMC' binoculars. This type of optical coating can transmit 85-90% of the light entering the binocular – which translates to significantly more light reaching your eye than with the lesser coating methods. Watch out for some manufacturers who claim 'Fully Multi-Coated optics' but actually use inferior Magnesium Fluoride coatings on the prisms – this is not a true FMC binocular. By their very nature, multi-coatings transmit light better over a larger area of the spectrum for better colour fidelity.
What is 'Exit Pupil Diameter '?
This is the diameter of the shaft of light coming from the binocular to your eye. It's easy to estimate this based on the objective size and the power. Exit pupil diameter roughly equals objective size divided by power. So for our 15x60mm binocular, the exit pupil diameter would be about 4mm. A larger exit pupil diameter is generally more desirable- especially for astronomical usage, since our eyes will dilate in darkness. The wider the shaft of light, the brighter the image because the light is hitting more of our retina. The reason a high-power binocular has a darker image is because a narrower shaft of light is reaching a smaller amount of retina. Note: Our specifications for Exit Pupil Diameter are from our actual measurements- not the factory published numbers.
What are Compact Binoculars and what can they do?
Generally include objective lenses not large than about 25mm (about 1') in diameter, they are foldable for compactness and ease of transport. Mini binoculars are small, lightweight, and highly versatile in their uses for, a mini binocular. Because of their relatively small objective lenses, however, mini binoculars are not intended for high resolution birding or other nature applications. Example: 7x16
Will I need a tripod to my binocular?
Tripods are pretty much a necessity for large binoculars, especially when used for astronomy. For most people, only binoculars of 11x or less magnification can be used for longer periods of time without a tripod (although even with low power binoculars, the view will be steadier, and more enjoyable, with a tripod).
Why are the 'Compact Binoculars' popular?
Considered as optical instruments, binoculars are available in different sizes. They come handy in portable models and widely available in today's market. Owning a pair should be a necessity when you're fond of the outdoors. If you're lazy to bring these heavy and gigantic binoculars with you, then a pair of compact binoculars is the best for you. They are lightweight, portable, and easier to carry everywhere you go. Compact binoculars are designed specifically for travelling people who want to avoid the hassle of carrying heavy things and still get almost the same viewing quality as giant binoculars. They are ideally used in hunting, bird watching, travellers, sporting, and those who enjoy the scenery of nature.
Ideally, compact binoculars are those that have lenses smaller than 30mm. The concepts behind them are still the same as telescopes except that it has two small telescopes physically attached together. Each telescope contains an objective lens, an exit pupil and an eyepiece. What makes compact binoculars easier to use is that they have smaller objective lens which makes them the top choice for some amateur outdoor enthusiasts. They are also foldable which makes them portable and convenient to store in any container. Like big binoculars, they are also protected with rubber to improve its durability. When you buy a new one, they are contained in a case and will have a hanging strip. Compact binoculars have so many designs to choose from, be it professional or for entertainment purposes like spectator sports, camping, hiking or just about any outdoor activity. There are also compact binoculars for bird watching exclusively. They are capable of providing bright images and wider view and sometimes have night vision and waterproof capability if you're on a rainy night adventure. These types of binoculars are really an indispensable tool to every outdoor enthusiast.
When you are a travelling person, having a portable and light luggage is a must. Whether you're a bird fanatic, a nature lover, a hiker, or a sports enthusiast, you will need convenient equipment that is not going to give you a hassle. Compact binoculars are one solution to the needs of people who love mobility when they are outdoors. Almost all people would surely want to travel light and having a pair of these small binoculars could mean simply ease in slipping them around one's neck or put them in small-sized pockets or bags. Compact binoculars are the answer when portability and mobility are required. Since they will have smaller lenses compared to bigger models, the light they collect will be lesser. So it's important to consider the quality of the optical activity in them. You should read for the manual for the product you're purchasing such as the quality of the glass used in the prisms and the lenses. Check also for the anti-reflection coatings used together with the optional features like waterproof and night vision. Compact binoculars are very efficient when you don't really need to look very far. When viewing with them, just try to get adequate light and as much as possible use them in a closed location. These can compensate for the lack of features you can find only in larger binoculars. Smaller binoculars can also work excellently in theatre-viewing or in small sport arenas. You can try out the Bushnell compact binoculars if you want extra-wide viewing area. These smaller binoculars are also ideal for children and beginners who are just starting to embrace the beauty of the outdoors. Upon constant usage of binoculars, you will acquire the experience needed to fully operate them to their maximum efficiency.
Utilise Porro prisms or not roof prisms to invert the image and usually are styled to form-fit comfortably in the observer's hands; objective lenses are typically 32mm in diameter or less. As their name implies, compact binoculars, while larger than mini binoculars, are relatively small and easy to carry. For sporting events, as a gift item, or as a general-purpose travel binocular, compacts are extremely popular, because, again, for all but the most advanced applications; compacts provide a good trade-off between weight, performance and cost.
At this point of time, you may think about investing in the best compact binoculars available. If you're a regular user of giant binoculars, there will come a time you will need smaller ones. If you find something interesting on a day and need quickly out, you may find it convenient to just slip in a compact binocular just about anywhere on your clothes or gear. Your compact binocular could also serve as your backup in case your larger one is out of order.
Examples: 12x32 or 8-20x25 Zoom
What do the 'Standard Porro Prism Binoculars' can do?
Most binoculars referred to as general-purpose are standard Porro prism models. The typically large objective lens apertures, 35mm or more, of these models enable bright, high-contrast images on the entire range of viewing subjects, from sporting events, to long-range animal observation in the wild, to high resolution study of a bird feather structure. A moderately prices, high quality, standard Porro prism model is a binocular for almost any observing application. Standard Porro prism binoculars are available in a wide range of specifications and price points.
Examples: 8x40, 10x50 and 20x50
How do 'Zoom Binoculars' work?
Offer the convenience of zooming to higher or lower power at the touch of a finger. The 10-30x50 'Triple Zoom' model allowed powers from 10x wide-field to 30x high-power, and with high-resolution imaging and sharp image focus at all magnifications.
Most amateur astronomers avoid zoom binoculars due to inherent limitations with zoom optics. Some of the drawbacks are a significantly reduced field of view (compared to fixed binoculars at the same power) and typical use of BK-7 prisms. We used to feel that the advantages and convenience of the zoom feature was worth the trade-offs, but our initial enthusiasm for zooms has decidedly cooled with experience. We agree with the majority opinion of amateur astronomers and do not recommend them to those that are primarily interested in viewing the night sky- fixed-power binoculars are always preferable for astronomy. Nevertheless zooms are quite useful for nature studies, sporting events, occasional night sky viewing, etc.
What are the advantages of 'Standard Waterproof and Porro Prism Binoculars'?
It is important to protect our binoculars from rain, dust, mist, moisture, fog, fire, fingerprints or sunrays or just anything that can make binoculars function inefficiently. One of the most common threats is water. The optical surface is very susceptible to water so if you're planning on using binoculars on moist or rainy areas, waterproof binoculars are highly recommended.
Waterproof binoculars are purely resistant to fresh and saltwater. They are specially designed to deliver clear images even after immersed in water. Waterproof binoculars are made in the most strict quality standards. Before they are brought into the market, they are fully tested first if they can endure the maximum harshness of water. Most waterproof binoculars have a lens protector to drive away water from the objective lens and eyepieces to help eliminate glare which are caused by the droplets of water. Lens protectors of these types of binoculars have a special and unique coating to repel water droplets. Next to military applications, hunting perhaps is the second most likely to qualify in the wear and tear group. That is why, it is very vital to have your hunting binoculars waterproof. Whether you are hunting on dry climate or not, it is also important to take note that your binoculars must not fog internally. However, with the latest technologies today, this issue is not needed to be worried about as most of the manufacturers have come up with durable and waterproof products that is guaranteed to withstand to almost all kinds of elements.
Special types of these binoculars can float in water for maximum protection. They may also have the latest roof-prism design with coated optics to maintain the sharpness and brightness of images even at worst climates. Optical coatings are sometimes applied to help reduce glare for those wanting the clearest view as much as possible and a rubber armouring also provides a firmer grip to the user. Most people carry around binoculars freely instead of putting them in their case. Luckily, the latest weatherproof binoculars we have today can survive different types of bad weather. To be sure, binocular lens protectors have to be used at times. Lens caps get lost so easily so some have attached lens caps at the binocular. Fortunately, new binoculars coming out today have attached lens cap protectors so they are useable for such a long time at any season of the year.
Professional-level binocular resolution and performance are generally reserved for standard roof and Porro Prism models. Designed for advanced applications, such as for serious birders, standard roof prism binoculars are typically of 35mm objective lens aperture or larger; include sleek, straight-line roof prism styling; and incorporate the finest optical glasses, multi-coatings, and multi-element eyepieces. The result is bright, extremely sharp, high resolution images throughout the field of view, and with a level of image fidelity unobtainable in lesser binoculars. Though premium-grade standard roof prism binoculars are not inexpensive, they are usually treasured for a lifetime.
Examples: 9x32 or 10x42
What can 'Large Aperture Binoculars' do?
There is nothing quite like the view offered by large-objective binoculars. We offer from 60mm to100mm extra large objective lens. The 3-D quality of the stereo image can be breath-taking, and just cannot be matched by the 'flat' view from a single-ocular telescope. Large aperture binoculars offer phenomenal performance for astronomical viewing. They are also a great choice for terrestrial use, especially from long distances.
What's the difference between BAK4 and BK-7 prisms?
BAK4 prisms (barium crown glass) are the highest quality available. BK-7 prisms (borosilicate glass) are also good quality, but sharpness falls off slightly at the edge of the field compared to BAK4.
How to Clean Binoculars?
- Purchase lens paper and special lens cleaning fluid.
- Blow hard on one of the lens to get loose debris and dust off of it.
- Brush the lens off lightly with a piece of lens paper.
- Wet a lens paper with the cleaning fluid and lightly wipe off the lens. Use a circular pattern.
- Take a dry lens paper and wipe any Wet fluid from the lens.
- Repeat for the other lens. Use a soft cloth that is barely damp with water to wipe off the exterior of your binoculars.
You can buy lens paper and cleaning fluid at a store that carries camera supplies. Do not use your shirt to wipe the lenses. You may very well scratch them.
Can I use my binoculars to observe the moon and planets?
Binoculars can offer outstanding low-power views of the moon, creating an impressive 'three-dimensional' effect that isn't possible with the single eyepiece of a telescope. However, in larger apertures the moon's brightness can become unbearable, and for this reason many of our larger binoculars are threaded to accept standard neutral density moon filters. Large aperture binoculars utilize extremely fast optical systems, so you can expect some minor flaring and chromatic aberration on extremely bright objects such as Venus and Jupiter (see the FAQ on 'false colour' below). Keep in mind that fixed-power astronomy binoculars were designed primarily for observing dim deep space objects, and their magnification is too low to see much planetary detail. If you are interested in primarily planetary observation and still want to enjoy the benefits of binocular observing, you'd be better off with one of our Binocular Telescopes. For casual observing, though, conventional binoculars of 15x-30x magnification can provide nice quick looks at the planets, as long as you recognize their limitations and don't expect them to perform like an expensive telescope. The amount of planetary detail you will be able to see is dependent on your visual acuity and the magnification of your binoculars. For example, for most individuals the ring of Saturn becomes clearly separated from the disk at around 20x in moments of good seeing, but for some it may take 25x magnification, while others will be able to see clear separation at 15x.
Could large-aperture binoculars offer the same image quality as my premium telescope?
Probably not, and certainly not if your telescope is an expensive apochromat. First of all, binoculars operate at much larger exit pupils than are typically used with most telescopes, which mean that the natural aberrations in your eyes will become more noticeable on bright objects. Also, let's consider the economics involved in producing a large-aperture binocular - for a typical, $370 100mm binocular, you are getting (2) F/4.5 doublet achromats, (2) prism clusters, and (2) wide-angle eyepieces, plus premium multi-coatings and all the mechanicals required to bring it all together and maintain collimation. We're not aware of any $185 100mm F/4.5 achromat packages than come with a high-quality diagonal, collimateable lens cell, and a wide field ocular, but if there were such a package, the performance expectations of any refractor aficionado would be pretty low. The point is that the performance per dollar being offered by most imported binoculars is amazing when you consider the price in telescope terms - that's why large-aperture binoculars are enjoying a surge in popularity
What is binoculars 'shockproof' for?
Don't be fooled by some manufacturers' claim that their binoculars are 'shockproof' or feature 'shockproof prism housings.' This is simply not true – there is no such thing as a 'shockproof' binocular. No matter how well a binocular is constructed, it can always be jolted out of optical alignment. That's why it's important to treat all binoculars with care - like the precise optical instruments that they are.
What is 'light gathering power'?
Objective lens size is the factor that determines how much light can potentially be collected by the binocular, and thus how deep you can see in the sky itself. Note that how much light actually gets to the observers eye is dependent on several factors, such as prism, size, baffling, and coating quality. In general, though, given similar coatings, you can use aperture to compare how much light will be gathered by two different binoculars. Because a binoculars' lenses are circular in shape, the area of the lens is inversely proportional to the lens diameter. In other words, a 100mm objective will gather four times as much light as a 50mm objective, even though it is only twice as far across.
What is 'phase-coatings'?
There is another type of coating process used on some binoculars, called 'phase-coating.' Because of their design, roof prism binoculars actually split incoming light into two separate beams as it passes through their prisms. Unfortunately, after they are split, the two paths of light become 'out of step' with each other. This in turn affects image quality. Phase coatings are applied to the roof prisms and are designed to re-merge the two paths of light for maximum performance. Because of their sophistication, phase coatings are normally found only on relatively expensive roof prism binoculars. Phase coatings are not applied to porro prism binoculars, because the porro prism design does not suffer from the same deficiency as roof prism binoculars.
What is the 'Near Focus' for?
Near focus indicates how close (in feet) you can be to an object and still maintain a sharp focus. For birding or nature studies, a near focus of 15 feet or less is recommended.
What are the Focus Types?
There are three main focus systems: centre, individual and permanent. The most common system is centre focus. A central dial is used to focus both sides at the same time. Best for viewing moving objects. Individual focus system binoculars are best for viewing slow-moving or stationary objects. Binoculars that have individual system focus are focused by turning each eyepiece. Lower quality binocular models may use permanent focus systems which produce inferior detail and no adjustment for differences in eye strength.
What are the keys for image quality?
RELATIVE BRIGHTNESS INDEX:
A binoculars ability to gather and transmit enough of the available light to give a sufficiently bright and sharp image defines its brightness. The brightness of a binocular also enhances colour differentiation in the image observed. R.B.I. (relative Brightness Index, Twilight Factor and R.L.E. Relative Light Efficiency are common indices used in the binocular industry, but are all somewhat flawed in their design and often prove fairly meaningless. Simply square the exit pupil - if your binocular has an exit pupil of 4mm, the relative brightness is 16 ( 4 x 4= 16).
Refers to the degree to which both dim and bright objects in the image can be differentiated from each other and from the background on the image. High contrast helps in observing fainter objects and in discerning subtle visual details. High quality optical coatings provide better contrast in an image. The other factors affecting contrast are: collimation, air turbulence, and objective lens, prism and eyepiece quality.
A measurement of the binoculars ability to distinguish fine detail and produce a sharp image. Better resolution also delivers more intense colour. Resolution varies in relation to the size of the binoculars objective lenses. Generally, a larger objective lens will deliver more detail to the eye than a smaller objective lens, regardless of the optical components, the type and quality of the optical coatings, atmospheric conditions, collimation (i.e. proper optical alignment), and the visual acuity of the user.
Why does only one eyepiece can be adjusted for my binoculars?
Because all eyes are slightly different, binoculars feature a Right Eye Diopter Adjustment. The purpose of this is to compensate for slight differences between a person's two eyes. With both eyes open, cover the right objective lens (front) with your hand. Turn the centre-focusing wheel until the image in the left side is sharp. Again, cover the left objective lens (front) with your hand and focus the right side by rotating the right eyepiece until the image is sharp. The binocular is now adjusted to your eyes. Make sure you're looking at the same object when calibrating each eye. Make a note of the diopter adjustment and turn the right eyepiece to that diopter adjustment whenever you look through them. Once you make this adjustment, you do not have to touch the diopter adjustment. Simply focus both sides by turning the centre wheel. If there are multiple users for the binoculars, they will need to be re-adjusted for each user.