Astronomy 512 -- Spring 2006 -- Assignment 4 -- Due Tuesday March 28

These problems are all meant to be worked individually. For 1) and 2) you are on your own (of course you can ask the staff questions...). For 3) you can consult heavily with the others in the class, but everyone should submit a unique solution to the problem.

  1. Calculate the focal length at a wavelength at 4.0um of a biconvex Germanium lens at a temperature of 100K which has radii of curvature of 2000 and 300 millimeters. If the lens is 50mm in diameter what is the focal ratio when the lens is used without a stop? Suppose you imaged the sky with this lens onto a focal plane, what is the resulting platescale in arcseconds/millimeter?

  2. Consider a 1 centimeter thick slab of Germanium at a temperature of 77K interposed in a f/3 beam of unaberrated monochromatic 8.00um light converging toward a focus.

  3. Consider an experiment to conduct wide field imaging of the sky at thermal infrared wavelengths in the L' and M photometric bands. Use Oslo to design a refractive imaging system with the following properties.

    This problem could be pursued with an extensive set of lenses. Fortunately, Oslo comes to the rescue (at least the EDU edition) by only permitting you 10 surfaces). You can allocate them however you like, but let this Oslo restriction set the ultimate complexity of your design. You should use spherical surfaces, but, if you want to be ambitious I will allow one aspherical surface in the design. If you wish, instead of placing that asphere on one side of a lens you can use that asphere as a reflective component in the re-imager part of the system.

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