PanoTools NG:
RE: calibrating a lens/teleconverter combo using PTGui
Yoram Bernet 2007-Dec-29 00:32:35
Erik:
I'm making slow progress. I'm looking at
http://erik-krause.de/index.htm?./verzeichnung/distort_en.htm, where it
recommends downloading the patched version of pano12.dll from
http://www.ueckermann.de/pano12/:. I get a 404 when I try to download from
this link. I'm pretty sure that I need the updated pano12 'cause I don't
have the dialog boxes that you show in the tutorial (my version is from
2001).
Where do I get the current version of pano12.dll?
Thanks,
Y
-----Original Message-----
From: #removed# [mailto:#removed#] On
Behalf Of Erik Krause
Sent: Friday, December 28, 2007 6:21 AM
To: #removed#
Subject: Re: [PanoToolsNG] calibrating a lens/teleconverter combo using
PTGui
Yoram Bernet wrote:
>
> I'm shooting close-ups of architectural models using a Canon 24mm TS lens
> combined with the Canon 1.4x teleconverter. Not surprisingly, the results
> show significant barrel distortion, especially near the edges of the
> image.
> I've tried correcting using PTLens but can only get so far as the
> particular
> lens/teleconverter/closeup combo is not specifically profiled in PTLens.
>
> I understand that it is possible to use PTGui to genberate a profile for
> my
> specific lens combo, then to use the profile to correct for the
> distortion.
>
To create a universal profile for a shift (and tilt) lens is virtually
impossible. Let's cover the shift lens first: A shift lns covers a much
larger image circle than the sensor/film sees. By shifting the lens you
effectively choose a part of a much larger image. Lens distortion is
symmetrical to the optical axis. Hence you see more or less distortion on
one image side depending from the amount and direction you shift. In other
words: The optical axis doesn't hit the image in it's center.
Panotools lens correction model can take care of this fact by shifting the
center of correction with the d and e parameters. However, to correct a
single photo you would have to know where exactly that center is. It can not
be optimized like in a panorama, where there is information from different
images available.
For details see http://wiki.
<http://wiki.panotools.org/Lens_correction_model>
panotools.org/Lens_correction_model
There are two workarounds for that situation:
1: Use a standard lens for shooting and correct perspective afterwards
(simulate a shift lens):
http://wiki. <http://wiki.panotools.org/Perspective_correction>
panotools.org/Perspective_correction
2: Try to correct distortion in the image directly. This is only possible,
if you have several straight lines in different distances to the image
center. A short howto is found on
http://erik- <http://erik-krause.de/verzeichnung/distort_en.htm>
krause.de/verzeichnung/distort_en.htm
Note, that you need to optimize for d and e shift parameters as well, since
the optical axis is not in the image center. Your result image will be
d-centerd in much the same as if you used perspective correction. Hence you
should carefully rea the above articles.
You could save the result of the above correction and reuse it for shots at
exactly the same shift settings. If you use your TS-E tilted your only
possibility is the second described above.
Lens distortion is not aperture dependent, but it is focus distance
dependent. So if you use your lens at very short distance, the necessary
lens correction might be different.
best regards
Erik
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