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Magnetic field close to the optical axis is approximately homogeneousRays starting at P intersect intersect the optical axis again in P.P is an image“ of P.What about rays starting in P at different angle?Larger angle means smaller distance between P and PPoint source imaged with an aperture of size 10 nm-1x in nmy in nmImage is an Airy-disc with diameter approx. 0.1 nmt=3.83Axial astigmatismAstigmatismMeridional en sagital raysComaLateral magnification not constant- creates a comet-like tail to each pointpositive comaDepth of focusDepth of field
