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See back focal plane using telescope
The rear focal plane of the objective can be observed using a telescope insert into the eyepiece tube.
Diffraction pattern in the transform plane
Demonstration of diffraction patterns in a test object - (Diatom test slide).
Spatial filtering in the transform plane
Using a small aperture slider to remove diffracted orders in the transform plane eliminates detail in the image plane.
Acceptance angle vs working distance
Working distance decreases with increasing acceptance angle.
Numerical Aperture vs useful magnification
A quick estimate of useful magnification:
N.A. X 1000.
Deriving Numerical Aperture = N.A.
The geometries of diffraction patterns must match the geometries of acceptance angle.
Importance of Condenser N.A.
Condenser N.A. must at least match that of the objective to realize full resolution.
Fourier musical analogy
Complex frequency-based information can be decomposed into combinations of simple waveforms.
Object detail vs. acceptance angle
The finer the spatial detail in an object the wider the diffraction angle - easily seen with a laser pointer and a fine grating.