POSITION CORRECTING METHOD OF PROJECTION LENS

摘要

PURPOSE:To improve precision by using the movement extent of a projection lens at a reference magnification position up to the detection position of a position detector as an extent of correction, and positioning the projection lens where reference magnification is obtained to the fitting position of the position detector. CONSTITUTION:The projection lens is set at a temporary unmagnification position and then a previously calculated position correcting value LADJ is inputted 26 as the number L of steps to move the projection lens to a real unmagnification position. Then, the absolute position of the projection lens corresponding to unmagnification as the reference magnification is calculated by the function (f) of magnification and the position of the projection lens and substituted 28 in a register LPOS indicating the current position of the projection lens. Relative movement is performed on the basis of the position LPOS to position the projection lens. The projection lens at the real unmagnification position is moved to a photointerrupter provided on an enlargement side to set the position correcting value on the basis of the movement.