adjustablefocus

Adjustable focus refers to the ability of an optical system to change its focal point, allowing for clear vision at different distances. This is a common feature in many optical devices, including eyeglasses, cameras, telescopes, and microscopes.

In eyeglasses, adjustable focus lenses, often referred to as progressive lenses or multifocals, allow the wearer to see clearly at near, intermediate, and far distances without switching glasses. These lenses have a gradual change in magnification across their surface, with the top typically for distance vision, the middle for intermediate, and the bottom for near vision.

Camera lenses utilize adjustable focus mechanisms to ensure that the subject being photographed is sharp. This can be achieved through manual adjustments by the user, who physically moves lens elements, or through autofocus systems that automatically detect the subject and adjust the lens accordingly.

Telescopes and microscopes also employ adjustable focus to bring distant celestial objects or microscopic specimens into sharp view. This usually involves moving the eyepiece or objective lens relative to the main body of the instrument. The principle behind adjustable focus in all these devices relies on altering the distance between the lens elements and the image sensor or the observer's eye, thereby changing the focal length of the optical system.