Use PTLens to correct barrel distortion in composite shift lens image.

[hyalinejim]

I have four shift lenses, some of which exhibit pronounced barrel, or
moustache distortion.

I would like to correct this. One option would be to use PTLens in
Photoshop but the size of the canvas required means I run out of
memory.

I remember that PTGui can generate lens distortion parameters for
lenses based on stitching a 360 degree panorama.

This might sound crazy, but can I do the same for my shift lenses. I
need correction paramaters for the final stitched image, generated
from the lens at maximum shift in a all directions.

I was thinking I could make a whole bunch of these composite shifted
images, (shift lens in all directions and take photos, move pano head,
shift lens in all directions again ,etc.) and then try to stitch them
into a 360 panorama in order to get the correction parameters for the
shifted composite images.

Am I actually crazy or is there an easy way (maybe line control points
on one composite image)?

Two problems occur to me: parallax distortion caused by shifting the
lens and also black borders at the corners of the shifted composite
images.

Any help appreciated, as some of these lenses are unusable for
architecture as the distortion is so poor.

I can upload files if that helps?

[PTGui Support]

What you could try is create a small panorama with the lens set at the
specific shift that was used for the image that you need to correct.
I.e. after shooting that photo, rotate the camera a bit and take 2 more
overlapping photos.

This panorama can be used to calibrate the distortion, load the panorama
in PTGui, be sure to optimize for lens shift. The resulting a/b/c and
d/e parameters should be usable for correcting the photo. Just create a
1-photo panorama from your source image, manually entering the a/b/c/d/e
parameters.

Joost

[hyalinejim]

Hi Joost,

that's a good suggestion. But if I understand you correctly I guess I
would have to do that for every shift configuration that I might use
(every direction and every amount of shift). I thought it might be
useful to have the parameters for the whole of the shiftable area,
given that I might need to correct a photo (or two or more stitched)
anywhere within that range.

It would then be a simple matter of taking a reference photo at the
unshifted position and stitching this with the other(s) in order to
register the other(s) position in shiftable space, and correcting the
whole lot, then croppping.

PS: I believe the subject heading should remain "Use PTGui to
correct......" as I am already trying to use PTLens (unsuccessfully
until I go 64 bit, I think).