We propose a novel design of panoramic annular lenses (PAL) for the imaging of 360° surroundings
with a large field of view (FOV) ranging from 30°~105°, which can partly realize the zooming function.
Its wavelength band is between 486 and 656 nanometers. The conventional vari-focal PAL is based on
the axial shift of some optical components, which will make the blind zone larger and out of the
sensing area, while our design is based on the lateral shift, which can make some imaging area zoom in,
keep the area of blind zone stay the same, and minimize the whole scale of this system. In order to
change the focal length of conventional PAL system, we introduce several pairs of free-form surfaces
(Alvarez surfaces) which can be regarded as several plano-spherical lenses and change the focal power
of the whole optical system. As we set two different configurations (long focal length and wide angle),
all of the optical parameters are designed and optimized with the help of the software (Zemax).
A new improved design method of the panoramic annular lens (PAL) with aspheric surfaces is introduced. The structure
is not only helpful to enlarge the field of view (FOV) of the system, but also help to make a horizontal symmetric field of
view. The field of view reaches (-30°—+30°)x 360 and was distortion controlled to reduce blind zone in the center.
The field of view and distortion of PAL was investigated theoretically and method of aspheric surface design was also
discussed. An aspheric PAL and its relay lens group were designed. The total length was 20.4mm, and the focal length
was 0.3mm. To get bright and clear image, the aperture of the system was set to f/2.88, and the diameter was 16.6mm.
The spectral range was from 0.486~0.656um. The relay lens group was consisted of 8 pieces of lenses, with a back focal
length (BFL) of 2mm. MTF below 70 lp/mm of the system is above 0.5. The result shows that the aberrations are
corrected well.
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