Multi-beam zoom lens for producing variable spot sizes for a laser printer

An optical system for exposing multiple image pixels on a medium using individually modulated light sources wherein each light source emits a light beam parallel to the each of said other light beams and an optical axis of said optical system, wherein a numerical aperture of each light beam is greater than or equal to 0.125 or F-number smaller than F/4.2, comprising:

• an optical subsystem comprising an afocal zoom lens with three or more independently internal moving groups;
• said optical subsystem having a constant barrel length of less than 125 millimeters;
• said optical subsystem having a constant distance from said light sources to said medium of less than 150 millimeters;
• and
• wherein said zoom lens has an afocal magnification change of at least 45% across a zoom range.

A printer for producing variable spot sizes on a media comprising:

• a plurality of light sources wherein each of said light sources emits a light beam parallel to each of said other light beams and parallel to an optical axis;
• wherein a numerical aperture of each of said light beams is greater than 0.125;
• an afocal zoom lens comprising a first moving group of lenses, a second moving group of lenses, and a third moving group of lenses;
• wherein a constant barrel length of said afocal zoom lens is less than 160 mm;
• wherein said zoom lens has a first constant distance from said light sources to said medium of less than 180 mm;
• and
• wherein said zoom lens has an afocal magnification change of at least 45% across a zoom range.