Method for preparing a lithographic printing plate

A method for preparing a lithographic printing plate, comprising the steps of:

• (a) exposing information-wise an imaging element, the exposing step comprising:
• (i) generating a modulated writing light beam having a wavelength to which the imaging element is sensitive;
• (ii) directing the writing light beam to a moving optical device to cause the writing light beam to scan across the surface of the imaging element in a first scanning direction;
• (iii) generating a reference light beam having a wavelength to which the imaging element is insensitive;
• (iv) directing the reference light beam to the moving optical device simultaneously with the writing light beam to cause the reference light beam to scan across the surface of a light detector element in the first scanning direction to generate signals indicative of the position of the writing light beam on the surface of the imaging element;
• and
• (v) moving the imaging element in a second scanning direction in response to the signals generated by the light detector element;
• and
• (b) processing the exposed imaging element by a diffusion transfer process which comprises developing an exposed silver halide layer in the presence of a silver halide solvent, to transfer a silver halide complex to an image receiving layer to form an image in the image receiving layer.