Wide-angle optical system, lens unit, and imaging apparatus

A wide-angle optical system comprising, in order from an object side:

• a negative first lens that is a glass lens having:
• a convex shape on the object side,
• a concave shape on an image side, and
• a spherical surface on either side;
• a negative second lens that has:
• an aspherical surface on at least one side, and
• a concave shape on the image side;
• a positive third lens;
• an aperture;
• a fourth lens that has an aspherical surface on at least one side;
• and
• a fifth lens that has an aspherical surface on at least one side,
• wherein conditional expressions (1) and (2) are satisfied,
• 0.27≤D14/D1L≤0.37 (1)
• 0.65≤D24/SAG2≤0.85 (2)
• where
• D14:
• a distance from an object-side surface of the first lens to an image-side surface of the second lens on an optical axis,
• D1L:
• a distance from the object-side surface of the first lens to an image-side surface of the fifth lens on the optical axis,
• D24:
• a distance from an image-side surface of the first lens to the image-side surface of the second lens on the optical axis, and
• SAG2:
• a SAG amount at an optical surface edge of the image-side surface of the first lens.