Telescopes

November 10, 2019 - 65 files posted from Handbook of Optics

         Making models from the prescription in the Handbook was straightforward.  The prescriptions generally are scaled to an entrance pupil diameter of 200mm, and generally shown with only an axial field point.  For the sake of continuity, I generally built the models with the same field of view.   I suspect that this field of view is wrong for all reasonable applications.  I also ignored obscurations.

January 24, 2017 - Four files posted

    These files are mostly of unobscured all-reflective designs.  This class of designs is interesting because it generally takes full advantage of modern methods for making aspheric optics.  I've never worked with such systems, but the look like they'd be lightweight and compact.  Unfortunately, complex coordinate transformations are necessary to define the system clearly, complicating the task of building models from the patent disclosures.

August 15, 2018 - 17 Gabor variants posted

              David Shafer’s recent article in Optical Engineering   contains many schematics of what’s come be known as the Gabor design.  He cautions that many of these designs are not especially useful as they stand, because of needing a curved image and not having color correction.  Instead, they are generally meant to illustrate three points:

              1) Even simple designs can have multiple solution regions and those should be explored.

              2) Very high performance with very simple designs can be achieved if a curved image is allowed, and

              3) Good starting points for further complexity can be generating by a solid understanding of aberration theory and prior design history

Furthermore, I’d like to note that this set of models is further evidence that the prescriptions contained in patent literature can be misleading.  Gabor’s British patent (#544,694A) is not well corrected, and optimum performance places the stop far from the concentric position as described in Shafer’s paper.  The model is included here anyway;  it’s fun to re-optimize such classic designs, pretending to be a better designer than the people from long ago.

              I needed help to generate some of these models.  I was able to generate models that looked very much like the figures, but straightforward optimization drove the system to other solutions, with much worse performance that David describes in his paper.  David kindly helped me, though, sending several complete prescriptions.  More importantly, he helped with some insight.  Some of the designs balance large aberrations across surfaces; this balancing is likely to give local minima in merit functions.  Figure 6  ()  in the paper is an example of such a system.

              Let me close by noting what a tremendous resource David Shafer has been.  He’s helped a lot with generating of these models.  More importantly, he has a long history of instructive and thought-provoking publications, many of which are summarized on his slideshare (https://www.slideshare.net/operacrazy) account.  I’ve always enjoyed reading his work; after this exercise, I can attest that his papers all deserve detailed study, by building models or working through the aberration theory.

Listing of design files: