An infrared imaging lens that produces beams with long focal depth while preserving the entire aperture for full light capturing and high transverse resolution is presented. Based on the conjugate-gradient algorithm, a diffractive optical lens with four times depth of focus improvement at the 10.6-μm wavelength has been designed and fabricated. ZEMAX simulation has confirmed the designed lens performance showing legible images over an extended image range. Through laser direct-write photoresist patterning and subsequent reactive ion etching on a germanium substrate, we have realized a diffractive lens with four times depth of focus improvement over a conventional infrared lens of the same numerical aperture. The extended depth of focus lens should yield a variety of applications in focus-free imaging without reducing lens aperture.