Lecture 8

# Lecture 8 - Lecture 8 Lecture 8 Achromat Design Design...

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Lecture 8 1 © Jeffrey Bokor, 2000, all rights reserved Lecture 8 Achromat Design – Design starts with desired – Next choose your glass materials, i.e. – Find , then get – Choose radii (still some freedom left in choice of radii for minimization of monochromatic aberra- tions). A common, simple choice is to make the crown lens biconvex, and to cement the two lenses together, with no gap. This means: biconvex cemented Then is set by the constraint of Eq. (7.3). For crown glass facing parallel light, this gives a good design to minimize spherical and coma. It can be fine tuned by careful choice of Example: Design 10cm focal length cemented doublet using the crown and flint glasses. note (checks!) Using biconvex for positive element with , n C n D n F n G’ crown 1.50868 1.511 1.51673 1.52121 flint 1.61611 1.6210 1.63327 1.64369 f D P D   P D P D  K K r 2 r 1 = r 1 r 2 r 1 == r 2 P D 10 D =  63.4783 =  36.1888 = P D 23.2611 = D P D 13.2611 D = P D P D P D +1 0 D r 1 r 2 = K 2 r 1 ------ P D n D 1 --------------- 45.5207 = r 1 0.043961m = 4.3961cm = r 1 r 1 = K 1 r 1 -------- 1 r 2 P D n D 1 ------------------ 21.3544 =

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Lecture 8 2 © Jeffrey Bokor, 2000, all rights reserved So, . This completes the design. Now check how well it works: Resolution limit of an optical system [Reading assignment: Hecht 10.2.6] Due to diffraction at the aperture stop, the image of a point is slightly blurred. Diffraction theory tells us that the image depends on the shape of the aperture. For a circular aperture: J 1 (x) is a special function called the “Bessel Function of the First Kind”.
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Lecture 8 - Lecture 8 Lecture 8 Achromat Design Design...

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