To exploit all beams transmitted through the microscope up to the information limit, one relies on a complex method called exit wave reconstruction which consists in mathematically reversing the effect of the contrast transfer function to recover the original exit wave "φe(x,u)". To maximize the information throughput, Hannes Lichte proposed in 1991 a defocus of a fundamentally different nature than the Scherzer defocus: because the dampening of the envelope function scales with the first derivative of "χ(u)", Lichte proposed a focus minimizing the modulus of d"χ"("u")/d"u"