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 biggest advantage of this category of binoculars has to do with the special combination of magnification and the size of the big lenses at the front, the objective lenses. These matters will now be discussed.How big objective lens size is ideal for all-purpose binoculars?Two factors determine what the apertures will be:?What the objective lenses are for and how much the instrument will weigh.Light enters the binocular through the apertures at the front of the instrument, which is the single most important element in how a binocular functions. Bigger lenses gather more light, but bigger lenses are heavier and this leads to a bigger instrument. Smaller lenses weigh less, but unfortunately do not gather the same amount of light as the bigger lenses. So manufacturers have looked for a golden mean between enough rechargeable light light gathering ability and not too much weight for a general purpose binocular?and the result is a binocular with objective lenses of 42 mm.: They gather enough light for excellent viewing throughout the day and are effective enough for reasonable viewing in low light conditions, but have only a moderate effect on the overall weight of the instrument.How powerful should a versatile binocular be?The following magnification is available in ordinary binoculars: 6x, 8x, 10x and 12x; more magnification power is associated with big and heavy binoculars for which tripods are needed. 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. 6x magnification power is too low and 7x is better, but still marginally below par for a versatile binocular. On the other hand, higher magnification like 10x and 12x causes certain restrictions: You will have the joy of more magnifying power, 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 focusing on an object (in particular when it抯 moving) very tough. With more power of magnification comes a restricted FOV, 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. So observing birds up close is not easy at all with high magnification instruments.The magnification which is a near-perfect compromise between the extremes, is 8x. You won抰 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 pupilThe exit pupil is the stream of light arriving at the viewer eyes on the other side of the binocular. 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. These will all be enough in bright daylight, but in low light conditions the smaller exit pupils will not be able to let enough light through for you to see a clear image. Optical glass and coatingsThe best compromise for an all-purpose binocular (8x42) will not ensure good images; the quality of the optical glass and prisms, as well as the optical coatings, play the decisive role.
