Fisheye correction
Also known as: fisheye removal, lens straightening
Reducing the barrel curve an ultra wide action lens produces, so a horizon stops bowing and verticals stop leaning inward.
Updated
What it means
Fisheye correction remaps the frame towards a conventional perspective. The lens bends straight lines increasingly towards the edges, and the correction pushes them back while giving up some width in exchange.
It is the same family of operation as Defishing and as Lens distortion correction, and the names are used fairly interchangeably. What varies is how strong the original projection was and therefore how much has to be given up.
The choice is editorial rather than technical. A corrected frame looks measured and slightly ordinary, while the uncorrected curve is part of why a Wide lens makes action footage read as fast and close.
How it works in practice
Cameras offer a corrected mode and editors offer a filter, and the difference is reversibility. A mode bakes the decision in, while a filter leaves the original available for a Rough cut to be reconsidered against.
Partial correction is usually the best answer. Straightening the horizon without fully flattening the frame keeps the energy and removes the obvious bow a viewer notices first.
Correcting consistently across a session matters more than the exact amount, since mixed geometry between shots is far more distracting than either choice applied throughout. Deciding once per session and sticking to it is the practical rule.
What to watch out for
Correction crops, so the usable resolution after it is lower than the file suggests, and stacking it with stabilisation tightens the frame further still.
Corners stretch rather than merely straightening. A face or a wheel at the edge of a strongly corrected frame elongates visibly, which is worse than the curve it replaced.
A tilted camera also corrects badly, because the remap assumes the lens was level. Fixing tilt with Horizon Lock before correcting gives a cleaner result than doing it the other way round, because a rotation applied after a remap fights the geometry it was given.
How RawClip handles it
Footage is scored and cut in its original geometry, because correcting first crops the frame and changes what the analysis sees. A camera that recorded in a corrected mode is simply read as the narrower shot it produced.