Telescopes

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:


 Design basis
 program image size
(1/2 diag, mm)
 f/#
 efl
(mm)

 Notes
US08011793 Zemax2003.5500 unobscured
US08184368 Zemax 7 4.4 200 unobscured
US08194318 Zemax 15 6.4 420refractive
US04733955 Zemax 12 4 40 unobscured
 GB544694A Zemax   1 Original Gabor patent
 Shafer-Gabor - fig 1 Zemax   100 
 Shafer-Gabor - fig 2 Zemax   100 
 Shafer-Gabor - fig 3 Zemax   100 
 Shafer-Gabor - fig 4 Zemax   100 
 Shafer-Gabor - fig 5 Zemax   100 
 Shafer-Gabor - fig 6 Zemax   100 
 Shafer-Gabor - fig 7 Zemax   100 
 Shafer-Gabor - fig 8 Zemax   100 
 Shafer-Gabor - fig 9 Zemax   100 
 Shafer-Gabor - fig 10 Zemax   100 
 Shafer-Gabor - fig 11 Zemax   100 
 Shafer-Gabor - fig 12 Zemax   100 
 Shafer-Gabor - fig 14 Zemax   100 
 Shafer-Gabor - fig 17 Zemax   100 
 Shafer-Gabor - fig 18 Zemax   100 

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