The minimum focusing ability is very useful in certain disciplines such as ornithology (bird watching) and even entomology (insect observation) and others, it allows us to clearly focus on animals (birds, butterflies, dragonflies, amphibians and reptiles, etc. ) a short distance, watching them in detail. The so-called "focus to infinity" also should be checked. This ideal is to focus a distant object straight silhouette (an antenna or pole is ideal) and check the result: a prism of a certain quality you see a clear image in a bad double image. Some models of binoculars on the market (eg STEINER.) Lack of focus ring, as they are made to provide insight clear at any distance from a minimum distance (around 10 to 20 meters). These models are very useful in applications for water sports, hunting, and the observation that in general do not require a vision at close range, but are inappropriate for others, especially ornithology (bird watching), which are often seen very close detail . As a complement to the focus, the binoculars come equipped with a diopter corrector.
This mechanism may be located in the right eye or along the central cylinder of focus. Its mission is to correct the possible difference in vision between the eyes, to achieve a perfect image sharpness. The classic method of adjustment is to focus an object (newspaper or billboard ideal commercial) with the left eye, moving the focus ring, and then with the right eye and moving the diopter adjustment sharp focus the image.