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Inoptics andphotography,infinity focus is the state where alens or other optical system forms an image of an object aninfinite distance away. This corresponds to the point of focus forparallelrays. Theimage is formed at thefocal point of the lens.
In simple two lens systems such as arefractor telescope, the object at infinity forms an image at thefocal point of theobjective lens, which is subsequently magnified by the eyepiece. The magnification is equal to the focal length of the objective lens divided by the focal length of the eyepiece.[1]
In practice, not allphotographic lenses are capable of achieving infinity focus by design. A lens used with an adapter for close-up focusing, for example, may not be able to focus to infinity. Failure of the human eye to achieve infinity focus is diagnosed asmyopia.
All optics are subject to manufacturing tolerances; even with perfect manufacture, optical trains experiencethermal expansion. Focus mechanisms must accommodate part variations; even custom-built systems may have some means of adjustment. For example, telescopes such as theMars Orbiter Camera, which are nominally set to infinity, have thermal controls. Deviations from itsoperating temperature are actively compensated to prevent shifts of focus.
