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Geometrical Optics and Lens Aberrations

Dive into the world of geometrical optics, lenses, and lens aberrations. Learn about chromatic aberration, spherical aberration, coma, field curvature, astigmatism, distortion, and more. Discover how these imperfections affect optical images and explore methods for correction. Explore the fascinating realm of optics and enhance your understanding of lens behavior.

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Geometrical Optics and Lens Aberrations

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  1. Geometrical Optics Chapter 24 + Other Tidbits

  2. On and on and on … • This is a short week. • Schedule follows • So far, no room available for problem session. Still working on it. • Today we try to complete lenses. • Quiz on Friday?

  3. Most important case: converging lensObject to left of F1

  4. Most important case: converging lens

  5. Most important case: converging lens

  6. Most important case: converging lens

  7. Most important case: converging lens So, now you know!

  8. Aberrations are imperfections in the optical image formed by a spherical lens (or optical mirror). There are five main aberrations:1.Chromatic aberration. The refractive index of glass varies with wavelength. This results in different focal lengths and image magnifications for different colours.2.Spherical aberration. Lenses with spherical surfaces have a shorter focal length at their periphery than at their centre.3.Coma. The various circular zones of a lens produce an image of an off-axis point that is distorted radially into a comet shape known as a coma patch.4.Curvature of field. The focal surface is not a plane but a bowl shape.5.Astigmatism. Because a lens appears asymmetric to an off-axis beam, the image of a point is not a point but a short line radial from, or tangential to, the optic axis of the lens. These images are formed in different planes.6.Distortion. The image magnification is greater towards the edges of the field (pincushion distortion) or less (barrel distortion) than at its centre.

  9. Remember the Spectrum?

  10. Dispersion • Index of refraction depends on the wavelength, or color. • f depends on the index of refraction.

  11. Chromatic Aberration

  12. Example

  13. Correction : achromatic lens couple

  14. Spherical Aberration • Results from the assumption of paraxial conditions. • Real lenses need a wider opening, larger apertures.

  15. Spherical Aberration - Correcting

  16. Barrel Distortion

  17. Coma

  18. Some useful stuff

  19. Diaphram Intensity~Area Fixed f stops will therefore go by factors of

  20. Camera • The intensity of the light striking the film or CCD array is proportional to the area of the lens. • This is adjusted by the photographer by means of the aperture or diaphragm control. • f-number is defined by • Ex: A lens of focal length f=50mm and an aperture diameter of 25mm has an f number of 2, often written as “f/2”

  21. f stops

  22. More on Camera

  23. The Microscope

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