Proceedings Article | 22 August 2009
Proc. SPIE. 7433, Optical System Alignment, Tolerancing, and Verification III
KEYWORDS: Optical design, Imaging systems, Lenses, Error analysis, Distortion, Cadmium sulfide, Panoramic photography, Spherical lenses, Tolerancing, Free electron lasers
Tolerancing a lens is a basic procedure in lens design. It consists in first defining an appropriate set of tolerances for the
lens, then in adding compensators with their allowable ranges and finally in selecting an appropriate quality criterion
(MTF, RMS spot size, wavefront error, boresight error...) for the given application. The procedure is straightforward
for standard optical systems. However, it becomes more complex when tolerancing very wide angle lenses (larger than
150 degrees). With a large field of view, issues such as severe off-axis pupil shift, considerable distortion and low
relative illumination must be addressed. The pupil shift affects the raytrace as some rays can no longer be traced
properly. For high resolution imagers, particularly for robotic and security applications, the image footprint is most
critical in order to limit or avoid complex calibration procedures. We studied various wide angle lenses and concluded
that most of the distortion comes from the front surface of the lens. Consequently, any variation of the front surface will
greatly affect the image footprint. In this paper, we study the effects on the image footprint of slightly modifying the
front surface of four different lenses: a simple double-gauss for comparison, a fisheye lens, a catadioptric system
(omnidirectional lens) and a Panomorph lens. We also present a method to analyze variations of the image footprint. Our
analysis shows that for wide angle lenses, on which the entrance pupil is much smaller than the front surface,
irregularities (amplitude, slope and location) are critical on both aspherical and spherical front surfaces to predict the
image footprint variation for high resolution cameras. Finally, we present how the entrance pupil varies (location, size)
with the field of view for these optical systems.
