Subminiature optical system and portable device including the same

An optical system, comprising:

• a first optical system;
• and
• a second optical system having an angle of view narrower than that of the first optical system,
• wherein the second optical system comprises a plurality of lenses sequentially disposed from an object side,
• wherein lenses disposed toward the object side are defined as a first group, and lenses disposed toward an image side are defined as a second group, based on a greatest distance on an optical axis between the lenses,
• wherein the first group has a total of three plastic lenses, including a first lens, a second lens, and a third lens;
• wherein the second group has a total of two plastic lenses, including a fourth lens and a fifth lens;
• wherein the fifth lens, disposed farthest from the object side among the lenses of the second group, has positive refractive power and at least one inflection point, and
• wherein the second optical system satisfies the following conditional expression:
• 0.7<TTL/F<1.0,
• where TTL is a distance on the optical axis between an object-side surface of the first lens, among the lenses, disposed closest to the object side and an image plane of an image sensor, and F is a focal length of the second optical system.