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Message: <blockquote data-quote="Hermann" data-source="post: 1311238" data-attributes="member: 4925">By far the most important factor controlling DOF in binoculars is the magnification. A second important factor, far more important than, for instance, eyepiece construction or effective f/number of the objective, is the accommodation range of the human eye. It thus depends to a large extent on the age of the user as the accomodation range decreases with increasing age.Taking 8x bins as an example, with the binoculars focussed to infinity: For a 30-year-old with an accommodation range of 7 diopters everything from 9.1 meters to infinity is sharp (8x8/7=9.1 meters). (Of course, in real life most people would refocus their binoculars at distances closer than, say, 30 meters or so, because it puts less strain on the eyes than continually focussing with the eyes.) For a 50-year-old with an accommodation range of 2 diopters things look rather different, for him the depth of field is a lot smaller, it's from 32 meters to infinity (8x8/2=32 meters).This may in fact be one of the reasons why many older birders I know tend to get binoculars with lower magnifications, the other reason being that they find it more difficult to hold their binoculars steady.Hermann</blockquote>