Optical system and image projection apparatus including the same

An optical system comprising, in order from an enlargement side to a reduction side:

• a front lens unit having negative refractive power;
• a stop;
• and
• a rear lens unit having positive refractive power,
• wherein the front lens unit includes a combination lens in which a negative lens and a positive lens are adjacently arranged in order from the enlargement side to the reduction side, and
• wherein, when a focal length of the negative lens is fN, an Abbe number and relative partial dispersion of a material of the negative lens are νN and θN, respectively, an Abbe number and relative partial dispersion of a material of the positive lens are νP and θP, respectively, and a focal length of the entire optical system is fW, following conditions are satisfied:
• −20<fN/fW<2
• 0.01<[θN−(−0.01618νN+0.6415)]−[θP−(−0.01618νP+0.6415)]<0.20.