Variable magnification projection optical system and image projection apparatus

A variable magnification projection optical system comprising:

• in order from a magnification conjugate side to a reduction conjugate side,
• a first lens group having a totally negative refracting power and being stationary during changing of magnification;
• a second lens group having a totally positive refracting power and being movable during changing of magnification;
• a third lens group having a totally positive refracting power and being movable during changing of magnification;
• a fourth lens group having a totally negative refracting power and being stationary or movable during changing of magnification;
• a fifth lens group having a totally positive refracting power and being movable during changing of magnification;
• a sixth lens group having a totally positive refracting power and being stationary during changing of magnification;
• and
• an optical stop which is arranged at any position from a front of a lens arranged closest to the magnification conjugate side in the fourth lens group to a front of a lens arranged closest to the magnification conjugate side in the fifth lens group,
• wherein the fourth lens group is configured to include, in order from the magnification conjugate side, two or more negative lenses and a positive lens, and
• wherein the following condition expressions (1), (2) and (3) are satisfied:
• |ET/fT|≧10 (1)
• |EW/fW|≧15 (2)
• 0.87≦φ23T/≦φ23W≦1.15 (3)
• wherein,
• ET;
• a paraxial exit pupil position at the telephoto end
• EW;
• a paraxial exit pupil position at the wide-angle end
• fT;
• a focal length at the telephoto end
• fW;
• a focal length at the wide-angle end
• φ23T, a composite refracting power of the second and third lens groups at the telephoto end
• φ23W;
• a composite refracting power of the second and third lens groups at the wide-angle end.