Mid Sized Binoculars Instruments with lenses around 30mm to 32mm are considered a mid-sized instrument slightly favor portability over the light gathering ability. So whilst they are perfectly fine for use during the day, they are not the ideal choice in very low light.
Compacts Binoculars with lenses between 18mm and 28mm are usually referred to as compact binoculars. Here it is all about ease of carrying and portability. Thes binoculars work best in good light and are ideal for uses like hiking, camping, taking to outdoor sporting events, walking safaris, etc.
For more take a look at this article on Which Compact Binocular is Best. So we have established that the binocular numbers provide the magnification and the size of the objective lenses on a bino. The surface area of the objective lenses can be calculated, which determines how much light is captured by those particular objective lenses.
The two measures, magnification, and size of objective lenses relate to the field of view. Field of view is how wide an area is encompassed in the image seen through the binocular. As the size of the objective lens increases, so does the field of view. As the magnification on a binocular increases the field of view decreases.
So almost every 8x42 has a wider field of view than a 10x Just remember, other factors also affect the field of view, so two 10x42 from different manufacturers may have a different field of view. Also: The numbers do not indicate how much of the light captured is actually transmitted to the eye, as the quality of the materials used in the lenses and other components on the light path determines how much light is lost not transmitted. They also do not indicate the weight of binoculars, as more powerful magnification and larger objective lenses will increase the overall weight.
This may determine whether the binoculars can be used handheld or using a tripod or with a monopod. There are many other factors that influence the suitability of binoculars for a particular intended use.
How big is the eye relief? How large is the subject being observed? How far away will you be from the subject? When choosing a scope for your rifle, consider that as magnification increases, brightness diminishes. At 4X magnification, the image in the scope will be brighter with a 50 mm lens than with a 32 mm lens. Bigger lenses cost more, of course, and they also weigh more.
Depending on the type of hunting you do, higher magnification or brightness may not be worth the extra cost. At lower magnifications levels, a 50 mm lens won't provide a lot of extra light compared to a 40 mm lens, for example. Joe Steel is a Northwest-based editor, writer and novelist, former news editor of an outdoor weekly. He also was an editor at a Seattle-based political weekly and editor of a monthly business magazine.
Most wide-angle eyepieces have a shorter eye relief distance than this. Getting your eye physically closer than 10 mm will cause undue eye fatigue not to mention physical fatigue fighting off your automatic blink response. Eyeglass wearers need greater eye relief to compensate for the distance their glasses stand away from their pupils. Binocular eyecups come in multiple designs to provide longer eye relief. Standard rubber eyecups can be folded back to allow the lens of glasses to sit physically closer to the eyepiece of the optic.
Some of the newer and high-end optics have adjustable eyecups so the distance can be preset for comfortable viewing while wearing eyeglasses. These are designed with greater eye relief than 20 mm but they are generally not recommended. The problem with these are that they can be difficult to keep the circular area that is projected from the eyepiece both centered and in focus over your pupil. They also tend to "black out" unpredictably when the eyecup is collapsed.
Consequently, it might be better to use optics with a standard eye relief, and not be able to quite get close enough to see the whole field. While discussing what comes out of the eyepiece, we should consider the exit pupil. The exit pupil is the circular beam of light that comes out of the eyepiece of the optics. If you hold your binoculars at arms length and look at the eyepiece, you will see a bright circle of light on the eyepiece. The diameter of that circle of light is the exit pupil.
It is calculated by taking the objective diameter and dividing it by the power of the optic. The exit pupil has often been used as a measure of how bright a binocular is, under the premise that the larger the exit pupil, the more light there is coming out of the eyepiece. This is absolutely NOT true.
Given that the quality of optics is the same, the 10 X 50mm binocular is much brighter. The exit pupil measurement does have some use though. In bright light, your eye pupils are normally open to about mm. If the exit pupil of the binoculars is close to this number your eye must be directly centered over it in order to see through the optics. This can be important if you are on a bouncing boat where keeping your eye centered exactly over the exit pupil might be difficult.
Some articles claim that optics with larger exit pupils than your eye pupils are a waste of light. If the exit pupil was used as a measure of brightness this may be true, but only because brightness does not increase when the exit pupil exceeds the diameter of your eye pupil.
This is a key issue with compact binoculars. A pair of 10x28 or 8x21 compacts have an exit pupil that is less than 3 mm which can be especially difficult to center exactly over the pupils, and thus difficult to see properly with.
This is further complicated in dim light when your eyes dilate. By about the age of 40, our eyes reach a maximum dilation of about 5 mm, so if you're using binoculars in all light conditions you would want at least a 5 mm exit pupil. Exit pupil may indicate the ease of use but has no real value in reference to brightness.
This measurement fails to take into account optical glass quality and alignment of optical elements. These factors have a greater impact on how bright an image is delivered to your eyes. While on the topic, we should also mention the myth of twilight factor. This is another measurement based on the physical size of the optic and does not take optic quality into consideration. The twilight factor is derived by multiplying the objective diameter by the magnification and then taking the square root of this product.
This number may seem reasonable when comparing a 10x42 pair of binoculars that has a twilight factor of In reality, it has little validity since it is actually objective diameter that might make the 10x42 brighter than the 8x35 optic. This is immediately apparent if you compare an 8x42 with a twilight factor of As noted before, brightness declines as magnification increases. Again, this does not take optic quality into consideration that has tremendous impact on the perceived brightness of the optics.
Optics4Birding will meet or beat any advertised price on the same item. Call Toll-Free My Account Checkout Shopping Cart. Subtotal: Cart Close. Designation and Consideration Designation All binoculars are labeled with numbers delineating their size and magnification. Objective Diameter In the example above, the objective lens diameter is the 42 in the 8x42 designation.
Magnification Commonly in the past the most popular magnifications for field size binoculars were either 8 or 10 power. Weight The two most notable concerns with the weight are related to fatigue and the ability to hold steady.
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