[GregL65]

Is there a name for the perspective of an extreme wide angle rectilinear lens, after any barrel or other distortion has been fully corrected?

[aaacb]

It's just perspective, and it's determined by distance to subject. Which often happens to be smaller for wide angle lenses, and that's what you're describing. At the edge of the frame for close subjects, i think you get that distorted look because the depth of the subject is comparable to the distance from the camera.

[photoptimist]

As @aaacb said, it's just perspective. It's an unavoidable artifact of images made with central projection imaging (where the rays of light from the scene all pass through a single point or iris pupil and then are recorded on a flat sensor or film plane).

Moreover, this "distortion" is mathematically unavoidable and uncorrectable if you want ensure that all the straight lines in the real world appear as straight lines in the image.

But there is one way to correct it! Just stand close enough to the image that you replicate the ratio of the focal length to the format size. For example if you have a photo taken with a 12mm lens on a 36mm wide sensor camera(1:3 ratio), then standing 12" away from a 36" print will replicate the central projection geometry of that lens-camera combo and the UWA corner and edge distortions will be minimized.

[cmohr]

As said, just distortion caused by the lens to crush the image down, and correct it. IE the rectilinear bit.

Just as a note, I found that different lenses each had different amounts of distortion to the image when set at the same focal length, I did post up some samples years ago, ( can't find them at the moment) where, I took the same photo on the same camera on a tripod, with three different Sigma ultra-wide angle zooms, the 8-16, 10-20 & 12-24 all set to 12mm, and each had a slightly different look to them as the optics of each were doing different things to the image projected. I put it down to differing Barrel distortion of each lens.

[stevebrot]

Yep, just regular perspective, but "corrected" to make it look good on a flat display. If display were an IMAX theater screen, the projection would be different but the perspective the same.


Steve

[Papa_Joe]

There is a name for the mapping function of rectilinear lenses, i.e. for the way the lens projects the reallity onto the sensor plane.

The mapping function is called rectilinear for lenses. The broader term is gnomonic projection.
While all rectilinear lenses share the same mapping function, there are different mapping functions for Fisheye lenses.

If you want to look a bit deeper into the subject, you can find more information here. Beware, it is mind twisting, at least for me.
Rokinon 8mm vs. 10mm vs. Sigma 8-16mm vs. Pentax 10-17mm Ultra-wide Showdown Review - Rectilinear vs Fisheye | PentaxForums.com Reviews
Fisheye lens - Wikipedia
Gnomonic projection - Wikipedia

[Kerrowdown]

Is there a name for the perspective of an extreme wide angle rectilinear lens, after any barrel or other distortion has been fully corrected?

Aye... "Mistress" Pentax-A 15mm F3.5

Yeah... "Irix 11mm".

[MossyRocks]

It is just perspective distortion and it really shows with things that have a dramatic difference from various points to the center of focus. For example in this shot I was very close to the barn (probably only 6 to 10 feet), but the upper parts of the barn are all canted away as they are much farther from the center of focus of the lens than the parts straight out.

Just embrace the perspective distortion and don't worry about things. I specifically sought out an extremely low geometric distortion UWA since I use it a lot for shooting things at infinity that require stacking. It still shows perspective distortion for things at varying distances but playing with perspective is fun. Just like with my 17mm fisheye where that distortion can get really fun. The very low distortion of the lens I took the daytime barn shot with was useful for stacking the 143 shots used for this image so that I didn't end up with odd shaped stars since the other geometric distortion can cause all sorts of artefacts in astro shots.

[dms]

If you want to take very wide angle images and avoid the "distortion," a fisheye lens de-fished with fisheye hemi will correct for it. But anyway we really should not be calling it distortion. It's a natural effect of mapping objects from a wide plane onto the parallel sensor plane--as those near the edge are much further away.

[photoptimist]

If you want to take very wide angle images and avoid the "distortion," a fisheye lens de-fished with fisheye hemi will correct for it. But anyway we really should not be calling it distortion. It's a natural effect of mapping objects from a wide plane onto the parallel sensor plane--as those near the edge are much further away.

Yes, it's a natural effect but that doesn't stop one's wife from being quite irate when she appears at the edge of the frame in a wide angle lens photo.

"Does this UWA lens make me look fat?" Yes it does!

And blaming the math of central perspective geometries does not help!

[MossyRocks]

"Does this UWA lens make me look fat?" Yes it does!

I'm surprised you survived.