perterra
Well-known member
Can I have a vowel, Vanna?
"Rolling Bowl" is a term I coined based on the well known "rolling ball effect." The latter is due to angular magnification distortion and the former to excessive pincushion, but the effect is similar, the image appears to move over a curved surface.
With "rolling ball" it moves over a positively curved surface like a globe (hence, Holger's name for - the "globe effect") whereas with excessive pincushion the image appears to roll through a negatively shaped curves surface such as a bowl.
Both effects are created by the same general principle, the image at the center is a different size than the image at the edges of the field. When the image shrinks at the edges, as it does with angular magnification distortion, the smaller image appears to fade over the edge of a globe. In the case of excessive pincushion, the image appears smaller in the center and larger at the edges. It's the disparity of the image size that tricks the brain (or at least some brains, not everybody sees this) into thinking that the image is moving, which is most noticeable while panning the landscape or tilting the bins up and down a treeline.
Brock
Thank you kindly (Texas phrase)