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About Anamorphic Distortion and Rolling Shutter
Two of the parameters that are found on some or all of the lens distortion control parameters, anamorphic distance and rolling shutter, aren’t really lens distortion effects at all—it just seemed the most reasonable place to put those controls. They are similar to distortion—they mess up the images—but they can’t be described solely as 2-D effects.
Rolling shutter has been described earlier ; we won’t discuss it further here other than to point out that its controls can now be found on these lens distortion panels.
Anamorphic distance is an issue only in anamorphic lenses, and is described in detail in the separate Anamorphic Shots Guide. We’ll just describe it briefly here.
The motivating issue is that anamorphic lenses have rather different optics (curvature of the lenses) in the horizontal and vertical direction, in order to give their distinctive horizontal shrink. Part of what is often different, however, is the effective entrance pupil position, aka the nodal point or effective camera location, which is simultaneously in different locations in the horizontal and vertical directions. This explains a number of the odd behaviors of anamorphic lenses: different focus sharpness in horizontal and vertical edges (they are at different distances), focus breathing resulting in aspect ratio changes (as the H&V entrance pupil positions shift differently), and distance-dependent aspect changes, ie the infamous anamorphic mumps. While anamorphic mumps were nominally “solved” long ago, that solution was simply to sweep the problem under the rug, keeping the focus subject stable, by moving the changes to the background. That’s a problem for matchmoving, where most of what we’re tracking is in the background!
Anamorphic distance is the direct model for what is happening, changing the basic 3-D to 2-D perspective transform to have different distances in the horizontal and vertical direction. This permits shots from lenses with a non-zero anamorphic distance to be solved correctly, although it does complicate later processing. That’s what we discuss at length in the Anamorphic Shots Guide. In the meantime, just keep in mind not to just turn on Anamorphic Distance calculations as if it is a simple distortion parameter. It is impossible for any 2-D lens distortion to correct for anamorphic distance, so if you need it, you need it!
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