A wide angle fast speed unobscured freeform aspheric mirror design for the IR is shown to be enormous in size compared to an all refractive 3 element lens of germanium with conventional aspherics and better performance.

1. Godzilla’s freeform optics
design versus Bambi’s
conventional optics design
Dave Shafer
David Shafer Optical
Design
Fairfield, CT 06824
203-259-1431
shaferlens@sbcglobal.net

2. This technical
article about a
freeform mirror
design is from
September 2019.
It shows a wide
angle unobscured
fast speed design
for use in the IR
range of 8u-12u

3. The freeform mirror design is a real
monster in size, compared to its tiny
aperture size and focal length

4. Same Scale!
Freeform
aspheric
mirror
design
Conventional aspheric design
with germanium lenses
Both designs are 9.3 mm focal length,
f/1.39, and 30 X 40 degree field size

5. Three aspheric
germanium
lenses for 8u to
12u IR design
9.3 mm focal
length, 50
degrees field
diameter, f/1.39
An aspheric lens design of germanium is fairly compact relative to the aperture size and focal
length. The aspherics give very good image correction at the fast speed and wide field.

6. The aspheric germanium lens design has distortion over its 50 degree field
of view that is 50X smaller than the 5.5% of the freeform mirror design.
This simple 3 lens design is a
tiny Bambi in size compared
to the monster Godzilla of the
freeform mirrors design.

7. Because of the very small focal length color is not a problem. The
polychromatic MTF of the germanium lens design is very good, as
shown here.

8. Same Scale!
Freeform
aspheric
mirror
design
Conventional aspheric design
with germanium lenses
Both designs are 9.3 mm focal length,
f/1.39, and 30 X 40 degree field size

9. Movie actor inside Godzilla costume takes a tea break