1. An optical system for processing an image using a point spread function (PSF), the optical system comprising: one or more lenses; an image sensor for sensing an image formed by the lenses; and an image processor for recovering the image sensed by the image sensor using the PSF, wherein a back focal length (BFL) defined as a distance between a refractive surface of one of the lenses that is closest to an image-side and the image sensor, is controlled such that ΔPSF defined by Equation below has a value less than 100%, Δ ⁢ ⁢ PSF ⁡ ( % ) = PSF ∞ - PSF macro ( PSF ∞ + PSF macro ) ⁢ / ⁢ 2 × 100 , Equation where PSF∞: size of PSF at infinity, PSFmacro: size of PSF at a predetermined close-up shot distance.