Vision metrology with super wide angle and fish-eye optics

Photogrammetrists have generally made use of wide or super wide angle rectilinear lenses that are designed to reproduce straight lines in the object space as straight lines in the image space. This paper investigates the use of fish-eye optics as an alternative to the conventional super wide-angle lens for vision metrology. The fish-eye design, whilst still retro-focus in construction, rejects the design constraints of rectilinear imaging in exchange for more even illumination across the image format and the expectation of reduced lens aberration effects. By means of a series of practical comparisons, this paper will investigate the target image performance and practical usage of two off-the-shelf 35mm camera mount lenses, namely an 18mm focal length super wide-angle rectilinear lens and a 16mm quasi fish-eye lens. Investigations include: an image quality assessment of retro-target images of differing sizes; an analysis of the variation in retro-target image quality with lens aperture; the influence of the different lenses on the internal consistency of highly over-determined self-calibrating multi-station photogrammetric networks and; an accuracy test between networks obtained with each lens type against measurement of the same targets using an industrial theodolite system.