Patent ID: 6954292

Claim:
An image scan apparatus having a projection lens and an image sensor for photoelectrically converting an optical image of an original that is formed through said projection lens, said apparatus comprising: a thermometer for measuring a temperature of said projection lens; a support member for holding said image sensor and said projection lens, said support member being movable along an optical axis of said projection lens; focus control means for focusing said projection lens by controlling position of said support member along said optical axis, said focus control means carrying out a focus search operation for searching a focus position of said support member while moving said support member along said optical axis, at said focus position a focal surface of said projection lens being located on said image sensor; a first memory which stores said focus position obtained through said focus search operation as a set focus position, and a temperature of said projection lens measured through said thermometer as a set temperature; and a second memory which stores respective correction amounts on said set focus position in relation to temperature differences; wherein said focus control means obtains a temperature difference between a temperature of said projection lens measured during focusing said projection lens and said set temperature stored in said first memory, reads out one of said correction amounts from said second memory in accordance with said obtained temperature difference when said obtained temperature difference is less than a predetermined value, correcting said set focus position, stored in said first memory, with said read correction amount, to obtain a corrected focus position, and sets said support member to said corrected focus position.