Schematic diagram for a hypothetical projection imaging experiment. The illuminating beam propagates from left to right and the solid black lines indicate the boundaries of the illumination wavefront. The sample is depicted as a small black filled circle in the sample plane and as a black circle in the reference and image planes. The red lines depict the illumination's wavefront in the sample and image planes, which are not merely related by transverse magnification. The distorted shape of the circle in the image plane represents possible distortions of the speckle produced by the sample and the transverse phase gradients of the illumination.