The aperture of refractive X-ray lenses is limited by absorption and geometry. We introduce a specific simulation method to develop an aperture-optimized lens design for hard X-ray full field microscopy. The aperture-optimized lens, referred to as Taille-lens, allows for high spatial resolution as well as homogeneous image quality. This is achieved by the individual adaptation of the apertures of hundreds of lens elements of an X-ray imaging lens to the respective microscopy setup. For full field microscopy, the simulations result in lenses with both a large entrance and exit aperture and lens elements with smaller apertures in the middle of the lens.