Projection system and projection-type image display apparatus

A projection system comprising:

• a first lens unit that makes an enlargement-side image formation plane, which is located on an enlargement-side, conjugate with an intermediate image;
• and
• a second lens unit that makes the intermediate image conjugate with a reduction-side image formation plane, which is located on a reduction side,
• wherein the first lens unit has positive power,
• the second lens unit has negative power,
• a second-lens-unit intermediate-image-side first lens, which is provided in the second lens unit and closest to the intermediate image, has positive power,
• the following expression is satisfied:
• −0.3≤fU1/fU2<0
• where fU1 denotes a focal length of the first lens unit, and fU2 denotes a focal length of the second lens unit, and
• the first lens unit includes a first-lens-unit enlargement-side lens, a first lens group having at least two lenses each having negative power, and a second lens group arranged from the enlargement-side toward the intermediate image, and to change a size of an image projected on the enlargement-side image formation plane, the first lens group and the second lens group are moved along an optical axis with the first-lens-unit enlargement-side lens fixed to perform focusing.