Patent ID: 6353216
Filing Date: 2002-03-05
Classification: G02B

Abstract:
In an automatic focus system having a first light source of a first wavelength, a second light source of a second wavelength, a method of achieving optical focus distance for a target object, said method comprising the steps of:illuminating the target object with said first light source; stepping through a focusing range for said focus system; determining the maximum signal of a light beam of said first wavelength reflected off the target object for the entire focusing range, said maximum signal representing optical focal distance for the target object; illuminating the target object when at a focal distance corresponding to said optical focal distance with said second light source; measuring a signal D3 of a light beam of said second wavelength reflected off the target object, said signal D3 representing optical focal distance for the target object; measuring, on a substantially continuous basis, a signal D4 of a light beam of said second wavelength reflected off the target object; calculating the difference &Dgr;D2=D4âˆ’D3; and adjusting the focal distance to the target object in accordance with the sign and magnitude of &Dgr;D2.