Optical system, image pickup apparatus, on-board system, and moving apparatus

An optical system comprising, in order from an object side to an image side:

• a front unit having positive refractive power;
• an aperture stop;
• and
• a rear unit having positive refractive power,
• wherein the front unit includes, in order from the image side to the object side, a first aspheric lens, a first negative lens, and a first positive lens,
• wherein the rear unit includes, in order from the image side to the object side, a second aspheric lens, a second negative lens, and a second positive lens,
• wherein the first aspheric lens includes an aspheric surface having an inflection point in a section including an optical axis, and
• wherein the following inequality is satisfied:
• 2.5≤fG1/fG2≤20.0
• where fG1 is a focal length of the front unit, and fG2 is a focal length of the rear unit.