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Fisheye Lens Controls
The fisheye lens control panel handles all four fisheye lens types: equidistant, equisolid, orthographic, and stereographic, using up to eighth-order distortion.
When a fisheye lens type is selected, the field of view and focal length are different than for normal lenses. This is reflected in the Lens panel, as well as Sizzle/Synthia/Python scripts. The Known field of view option must be selected, with a value reflecting the expected/desired maximum field of view of the “ideal” undistorted perspective image. The focal length display will show the apparent lens focal length rating, based on the stated sensor size.
Note: These fisheye distortion models are true 2-D distortion models, converting the image to a standard perspective image. Consequently, they do not handle fields of view approaching or exceeding 180 degrees: only somewhere around 120 degrees can reasonably be converted to undistorted non-fisheye format.
Tip: For wide field of view fisheyes, including fields of view exceeding 180 degrees, use Lens Master Calibration to produce an STMap converting images from the fisheye format to 360VR equirectangular format.
The distortion coefficients are the parameters C2 to C8. HCTR, VCTR, and Rolling Shutter are discussed in the Shared Parameters section.
The Scale parameter controls how a nominal fisheye image is scaled up onto the physical image plane; the lens focal distance is computed from this value and the sensor size.
The AngFac value permits a tweak to the mapping function, especially for equisolid lenses (but also stereographic), as suggested by the wikipedia article’s note
(a). It should be kept at 1 in most cases.
Note that when significant distortion is present, or a different AngFac value, the relationship between Scale and the focal length becomes less likely. Similarly, when many distortion terms are present, the ability to discriminate between the various lens types is likely muddled.
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