# lecture34 - D i ffr a cti on a nd Li mi ts of Resol uti on...

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Diffraction and Limits of Resolution

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Diffraction through a circular aperture of diameter D Intensity Diameter D Image on Screen Because of diffraction, images formed by “perfect” optics are fuzzy.
For a circular aperture: The angle θ from the centre to first dark ring (“angular radius” of central spot) is: θ = 1.22 λ/D radians This is useful in calculating the limiting resolution of optical instruments (microscopes or telescopes). The central spot is sometimes called the Airy disk

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Example: Sodium light (589nm) is used to view objects under a microscope. If the aperture of the objective has a diameter of 0.9 cm, a) find the limiting angle of resolution (max resolution) if the space between the object and the objective lens is filled with water (n=1.3), how is the resolution affected?
Example: If the eye pupil is dilated to a diameter of 5mm, what the minimum distance between two point sources that the eye can distinguish at a distance of 1km?

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Quiz: What else can affect the resolution of a telescope?
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