Small lens system including seven lenses of +-+-+-0 refractive powers on the optical axis

A small lens system comprising a first lens, a second lens, a third lens, a fourth lens, a fifth lens, a sixth lens, and a seventh lens sequentially arranged from an object, wherein

• the first lens has a positive refractive power,
• the second lens has a negative refractive power,
• the third lens has a positive refractive power,
• the fourth lens has a negative refractive power,
• the fifth lens is convex toward the object, is concave toward an image, and has a positive refractive power,
• the sixth lens has a positive or negative refractive power and is provided on at least one of an object-side surface and an image-side surface thereof with a single inflection point or a plurality of inflection points, and
• the seventh lens has a positive or negative refractive power and is configured such that a radius of curvature (R71) of an object-side surface of the seventh lens and a radius of curvature (R72) of an image-side surface of the seventh lens satisfy R71=∞ and R72=∞, respectively, and
• a ratio (TTL/f) of a distance (TTL) between an object-side surface of the first lens and an image surface to an effective focal distance (f) of an entire optical system satisfies TTL/f<1.3.