Ideally, convex lens is optical element whose property forms image from parallel waves(light, electron) into lens at one point on back focal plane. The intensities on back focal plane have same intensity distribution as Fourier Space.
If the object is the far side of front focal plane, waves(light, electron) through the back focal plane are condensed again for each wave diffracted from the same point. Therefore, Therefore, an image which is called Real Image is formed at this position.(Imaging) By putting a recording element(e.g. Film, CCD, CMOS, and so on) at this position, it can record images.