The so-called focus to infinity should also be checked. So ideally, you focus an object of straight silhouette (an antenna or pole is ideal) and check the result: in a certain quality binoculars will be a sharp image, in a bad one a double image. Some models of binoculars on the market (e.g. STEINER) lack of focus ring, since they are manufactured to provide clear vision at any distance from a minimum distance (to 10-20 meters environment). These models are very useful in nautical applications, hunting and other activities of observation that in general do not require a very short distance vision, but they are inappropriate for other, particularly Ornithology (bird watching), where often you must appreciate very close details. As a complement to the approach, the binoculars are equipped with a diopter correction system. This mechanism may be placed in the right eyepiece or beside the central cylinder of approach.
Its mission is to correct the possible vision difference between both eyes, to achieve a perfect image sharpness. The classical method of adjustment is to focus on an object (ideally a newspaper or commercial sign) with the left eye, by moving the focus, and then, with the right eye ring and moving the diopter adjustment focus clearly the image. The end result should be an equally sharp vision with both eyes. Of course, models that do not have a diopter correction must be disposed. For users of glasses, some quality binoculars have eyepieces shrink, i.e., that they can put inward or bend the rubber that protects them to make comfortable vision with glasses. A feature of special importance from the viewpoint of a prismatic is its transmission capacity of color. This capability should be checked by comparing different models of binoculars, and will tend to choose that able to deliver an image bright and natural, without false colors, matting and distortions around the image.