If you’re looking for a pair of binoculars you can use everywhere, an 8x42 should be your choice, 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. They are bigger than the really small and compact ones, but smaller than the really outsize binoculars. Size is just one of the in-between features; more important are the power and apertures. These matters will now be discussed.
What should the diameter of the objective lenses be for versatile binoculars?
The choice is determined by two factors: The purpose of the big lenses at the front of a pair of binoculars, as well how heavy the binocular is going to be.
The purpose of objective lenses is to gather light, without which no image will ever reach the viewer’s eyes. Bigger apertures mean more light to work with, but bigger lenses weigh more and this implies a bigger and heavier binocular. Smaller lenses weigh less, but on the downside, gather less light as well. So manufacturers have looked for a golden mean between enough light gathering ability and not too much weight for a general purpose binocular and objective lens diameter of 42 mm. is just that: They are perfect for viewing when lots of light is available 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.
How powerful should a versatile binocular be?
The magnification of ordinary size binoculars vary from 6x to 12x; giant binoculars go as high as 30x. Magnification of 8.5 and 10.5 are also available. The 9x magnification always goes with giant binoculars.
Magnification of 6x is not powerful enough and 7x is better, but still not powerful enough for a versatile binocular. On the other hand, more powerful magnification like 10x and 12x causes certain restrictions: You may see more detail with a more powerful binocular, but the first implication of more power is a less bright image. Furthermore, more magnifying power is also associated with amplification of movement. The slightest motion, like normal hand tremors is amplified making finding an object (in particular when it’s moving) very hard. High magnification also causes a narrower field of view, which in combination with the problem of movement sensitivity, makes focusing on an object even more difficult. It also causes flatter depth of vision, which means that the viewer has to adjust the focus 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. It is powerful enough to make you see distant objects and to see a lot of detail the closer the object gets. However, 8x is not too powerful to have to contend with things like narrower field of view and movement sensitivity which come with more magnifying power.
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. A 10x42 has an exit pupil of 4.2 mm. and a 12x42 only 3.5 mm. No problem using binoculars with these exit pupils during the day 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 clear images considering the amount of light available.
Optical glass and coatings
The best compromise for an all-purpose binocular (8x42) will not guarantee excellent viewing; the glass used for the lenses and prisms as well as the optical coatings have to be of the highest quality.
About the author:
The author has written extensively on binoculars and is the owner of http://www.binocularsreviewed.net and http://www.pocketbinoculars.net . You could also visit his site on game reserves, http://www.madikwesafarilodge.net .