Page 87 - Fundamentals of Light Microscopy and Electronic Imaging
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70 DIFFRACTION AND INTERFERENCE IN IMAGE FORMATION
A
P P′
P′′
(a)
B
A
P P′
P′′
(b)
Figure 5-7
Aperture angle determines the size of the diffraction spot. Point source P and its conjugate
image P in the image plane. Point P is moved laterally in the focal plane away from P
until destructive interference at a certain distance determines the location of the first
diffraction minimum and thus the radius of the diffraction spot. (a) Points A and B in the
wavefront with full lens aperture. (b) Points A and B in the wavefront with reduced aperture
angle caused by partially stopping down the condenser iris diaphragm.
