Internal focus lenses (IF) for camera

Lenses with internal focus

— internal focus or Internal Focus (IF) means a special design of the focus system, in which focus is carried out by moving one or two groups of lenses inside the lens, without changing its physical dimensions. That is, in such models, the front lens and the outer parts of the lens remain stationary during focus, which increases the usability of the petal hood and some filters (polarizing, for example). Accordingly, when shooting, the photographer can safely hold on to the lens. Also, such a system does not draw dust into the lens, which will increase its service life. Usually internal focus is the prerogative of protected lenses, but sometimes it is also found among ordinary ones.