8X42: The Most Versatile Binocular
In the world of binoculars everybody agrees that 8x42 binoculars are the most versatile group, since they are the ones you can use for virtually anything you might be interested looking at through your binoculars and in any circumstances - all-purpose, all-terrain binoculars. As far as size is concerned, they are right between the two extremes: pocket binoculars and giant binoculars. The compromise also involves the features of magnification and objective lens diameter. These matters will now be discussed.
What should the diameter of the objective lenses be for versatile binoculars?
Two things play a role in deciding this feature: The function of the objective lenses and the weight of the binocular.
The big lenses at the front are for gathering light, without which a binocular cannot operate. Bigger apertures mean more light to work with, but bigger lenses are heavier and this implies a bigger and heavier binocular. Smaller lenses are not that heavy, but unfortunately let less light enter the instrument. The aim is to strike a good balance between these two factors for a versatile binocular and objective lens diameter of 42 mm. is just that: They gather enough light for excellent viewing throughout the day and supply enough light for reasonable viewing at dusk or dawn, when it's overcast or in the forest, but are not too big to make the instrument too heavy and bulky.
What should the magnification power of an all-purpose binocular be?
The power available in ordinary binoculars vary from as low as 6x (some cases even 4x) to 12x; beyond that you move into the realm of giant binoculars. Some binoculars with 8.5x and 10.5x magnification are also on the market. Power of 9x is associated only with big lenses of 63 mm.
Magnification of 6x is a bit too weak and 7x is better, but still not powerful enough for an all-terrain pair of binoculars. On the other hand, more powerful magnification like 10x and 12x causes certain restrictions: You will have the joy of more magnifying power, but the image will not be as bright. Furthermore, more magnifying power is also associated with movement sensitivity. The slightest movement, like "binoculars shakes" is amplified making finding an object (in particular when it's moving) very hard. High magnification also causes a narrower field of view, which aggravates the problem of movement amplification. It also causes flatter depth of vision, which means that the focus will have to be adjusted more often. Imagine how difficult it will be watching active birds at close range with binoculars with flat depth of vision.
Clearly the golden mean as far as magnification is concerned, is 8x. You won't have any problems getting a view of distant objects and to see enough detail at any range. However, 8x is not too powerful to let you suffer from the negative features associated with high magnification mentioned above.
Exit pupil
The exit pupil is the stream of light at the eye pieces entering the viewer's eyes. The exit pupil is determined by dividing the objective lens diameter by the magnification: 42/8 = 5.25 mm. So it follows that the exit pupil of a 10x42 is 4.2 mm. and 3.5 mm. in the case of a 12x42. Exit pupils this small will be quite sufficient when the sun is shining, but when the sun is not shining and conditions are dim the smaller exit pupils will let too little light through for you to see a clear image.
Optical glass and coatings
The best compromise for an all-purpose binocular (8x42) will not be your ticket to perfect viewing; the quality of the optical glass and prisms, as well as the optical coatings, play the decisive role.
What should the diameter of the objective lenses be for versatile binoculars?
Two things play a role in deciding this feature: The function of the objective lenses and the weight of the binocular.
The big lenses at the front are for gathering light, without which a binocular cannot operate. Bigger apertures mean more light to work with, but bigger lenses are heavier and this implies a bigger and heavier binocular. Smaller lenses are not that heavy, but unfortunately let less light enter the instrument. The aim is to strike a good balance between these two factors for a versatile binocular and objective lens diameter of 42 mm. is just that: They gather enough light for excellent viewing throughout the day and supply enough light for reasonable viewing at dusk or dawn, when it's overcast or in the forest, but are not too big to make the instrument too heavy and bulky.
What should the magnification power of an all-purpose binocular be?
The power available in ordinary binoculars vary from as low as 6x (some cases even 4x) to 12x; beyond that you move into the realm of giant binoculars. Some binoculars with 8.5x and 10.5x magnification are also on the market. Power of 9x is associated only with big lenses of 63 mm.
Magnification of 6x is a bit too weak and 7x is better, but still not powerful enough for an all-terrain pair of binoculars. On the other hand, more powerful magnification like 10x and 12x causes certain restrictions: You will have the joy of more magnifying power, but the image will not be as bright. Furthermore, more magnifying power is also associated with movement sensitivity. The slightest movement, like "binoculars shakes" is amplified making finding an object (in particular when it's moving) very hard. High magnification also causes a narrower field of view, which aggravates the problem of movement amplification. It also causes flatter depth of vision, which means that the focus will have to be adjusted more often. Imagine how difficult it will be watching active birds at close range with binoculars with flat depth of vision.
Clearly the golden mean as far as magnification is concerned, is 8x. You won't have any problems getting a view of distant objects and to see enough detail at any range. However, 8x is not too powerful to let you suffer from the negative features associated with high magnification mentioned above.
Exit pupil
The exit pupil is the stream of light at the eye pieces entering the viewer's eyes. The exit pupil is determined by dividing the objective lens diameter by the magnification: 42/8 = 5.25 mm. So it follows that the exit pupil of a 10x42 is 4.2 mm. and 3.5 mm. in the case of a 12x42. Exit pupils this small will be quite sufficient when the sun is shining, but when the sun is not shining and conditions are dim the smaller exit pupils will let too little light through for you to see a clear image.
Optical glass and coatings
The best compromise for an all-purpose binocular (8x42) will not be your ticket to perfect viewing; the quality of the optical glass and prisms, as well as the optical coatings, play the decisive role.
