Reduction optical system and image pickup apparatus

An image pickup apparatus comprising:

• a reduction optical system disposed on an image side of a main optical system, a composite focal length of the main optical system and the reduction optical system being shorter than a focal length of the main optical system;
• and
• an image pickup element configured to pick up an image formed via the reduction optical system,
• wherein the reduction optical system comprises:
• a first lens element disposed closest to an object side and having a positive refractive power;
• a second lens element disposed closest to an image side and having a positive refractive power;
• and
• a positive lens and a negative lens disposed between the first lens element and the second lens element, and
• wherein following conditional expressions are satisfied:
• 0.440≤fp1/f<1.500, and
• 0.600<fp1/fp2<2.500,
• where fp1 is a focal length of the first lens element, f is a focal length of the reduction optical system, and fp2 is a focal length of the second lens element.

A reduction optical system disposed on an image side of a main optical system, a composite focal length of the main optical system and the reduction optical system being shorter than a focal length of the main optical system, the reduction optical system comprising:

• a first lens element disposed closest to an object side and having a positive refractive power;
• a second lens element disposed closest to an image side and having a positive refractive power;
• and
• a positive lens and a negative lens disposed between the first lens element and the second lens element,
• wherein following conditional expression is satisfied:
• 0.440≤fp1/f<1.500,
• where fp1 is a focal length of the first lens element, and f is a focal length of the reduction optical system, and
• wherein the reduction optical system includes a first positive lens which satisfies following conditional expressions:
• 1.900≤Nph
• where Nph is a refractive index of the first positive lens.