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Ray tracing

For a fully general calculation of image quality, one does not wish to be limited to third-order aberrations, nor does one often wish to work out all of the relations for the complex set of aberrations which result from all of the sources of aberration mentioned above. Real world situations also have to deal with vignetting in optical systems, in which certain rays may be blocked by something and never reach the image plane (e.g., in a two-mirror telescope, the central rays are blocked by the secondary).

Because of these and other considerations, analysis of optical systems is usually done using ray tracing, in which the parameters of an optical system are entered into a computer, and the computer calculates the expected images on the basis of geometric optics. Many programs exist with many features: one can produce spot diagrams which show the location of rays from across the aperture at an image plane (or any other location), plots of transverse aberrations, plots of optical path differences, etc., etc.

Demo ray trace program. Start with on-axis object, single mirror. Where is focus? What will image look like with spherical mirror? What do we need to do to make it perfect? How does it depend on aperture size? Now how do off-axis images look like? spot diagrams, through focus, ray fan, opd plots, etc. Now introduce second mirror. What determines where focus will be? Magnification? What shape to make a perfect on-axis image? What do off-axis images look like? How do we make them better? Now how is performance? Real 3.5m and 1m prescriptions. Issue: guider.


next up previous
Next: Physical (diffraction) optics Up: Astronomical optics Previous: Aberration compensation and different
Rene Walterbos 2003-04-14