Optical system and camera module

An optical system comprising:

• a first lens to fourth lens arranged sequentially along an optical axis from an object side,
• wherein an object-side surface of the first lens has a convex shape on the optical axis,
• wherein a sensor-side surface of the first lens has a concave shape on the optical axis,
• wherein a sensor-side surface of the fourth lens has a convex shape on the optical axis,
• wherein the first lens is made of glass, and the object-side surface and the sensor-side surface of the first lens are spherical,
• wherein a center distance between the third lens and the fourth lens among center distances between the first to fourth lenses is a largest,
• wherein an optical axis distance from the object-side surface of the first lens to a surface of an image sensor is TTL,
• wherein an optical axis distance from the sensor-side surface of the fourth lens to the surface of the image sensor is BFL,
• wherein an optical axis distance from the object-side surface of the first lens to the sensor-side surface of the fourth lens is TD, and
• wherein the following Mathematical Formulas satisfy:
• 0.2<BFL/TTL<1 and 1<TTL/TD<2.

An optical system comprising:

• a first lens having positive refractive power;
• a second lens disposed on a sensor side of the first lens;
• a third lens disposed on a sensor side of the second lens;
• and
• a fourth lens disposed on a sensor side of the third lens, having positive refractive power and a convex shape on a sensor-side surface,
• wherein the first to fourth lenses are aligned with an optical axis,
• wherein an object-side surface of the first lens has a convex shape on the optical axis,
• wherein a sensor-side surface of the first lens has a concave shape on the optical axis,
• wherein a sensor-side surface of the fourth lens has a convex shape on the optical axis, and
• wherein a center distance between the third lens and the fourth lens among center distances between the first to fourth lenses is a largest.