Variable focal length projection lens for use on overhead projectors
AssigneeMinnesota Mining and Manufacturing Company
InventorDennis F. Vanderwerf
Life of this patent
Estimating the term…
Abstract
A variable focal length overhead projector lens having four elements positioned in a projection head with two elements on either side of a folding mirror and having a single movable negative lens element closest to the screen being movable to vary the focal length and magnification at a fixed object-to-image distance to fill the screen.
Claims4
A lens assembly for use in an overhead projector having a variable focal length to afford changes in magnification with fixed object-to-image distances as between the stage and the screen, said lens assembly comprising a first negative meniscus lens airspaced from a positive meniscus lens which is airspaced from a second positive double convex lens which is airspaced from a movable lens element which is a negative double concave lens affording a range of movement to change the focal length between about 276 mm to 356 mm and afford a change in the magnification by a factor of between 1.4.times. and 1.5.times., and a mirror positioned between said positive lenses to fold the light path.
Dependencies are inferred from the claim text.