This document contains contact information for David Shafer of David Shafer Optical Design and describes an unobscured 6 inch aperture f/10 telescope design from 1990. The design uses BK7 lenses and spherical mirrors to produce a diffraction limited image over a 1 degree flat field with no tilt at f/10 and has a length approximately equal to the focal length. It also references a simplified version of the design from a slideshare presentation that has a shorter length of half the focal length using tilted lenses and spherical mirrors with an optional fold flat.

1. Dave Shafer
David Shafer Optical Design
Fairfield, CT 06824
203-259-1431
shaferlens@sbcglobal.net
An unobscured 6 inch aperture f/10 design

2. f/8 spherical
mirror
Fold flat
BK7 lenses
f/8 tilted
image
https://www.slideshare.net/operacrazy/a-simple-unobstructed-telescope-with-high-performance-1990
Design data for this design from 1990 is given here
Long length to design, about = focal length

3. f/6.33
f/10 flat image, no tilt
Tilted BK7 lenses
Two tilted spherical mirrors

4. Fold flat
Spherical
secondary
mirror
Spherical
primary
mirror
Tilted
BK7
lenses
Diffraction limited in visible
over a 1.0 degree flat field
diameter. Image has no tilt.
f/10
f/6.33

5. This design, with or without a fold flat, has a length that
is ½ of the focal length = much shorter than the first slide