Judy,
Most of the zoom lenses on cheaper digital cameras have considerable
barrel or pincushion distortion, and PTLens can correct this. It is
obviously more noticeable on subjects with straight lines, such as
architecture, but other things do look different after processing. Of
course the distorted version may look better.
Working close-up may produce different values of barrel or pincushion
distortion, and if it was important to get things correct you would
probably want to shoot a suitable test target with plenty of straight
lines at the same distance (and to cover the range of focal lengths you
use - the program extrapolates for focal length values between those you
calibrate.)
Panorama Tools (PT) is a set of routines first written quite a while back
for correcting images, and its main use is in correcting the various parts
of a multi-image panorama so they will fit together. You can also convert
from one perspective to another - so I can take images shot in cylindrical
perspective on a swing lens camera and convert to rectilinear should I
wish. It is a powerful set of tools for manipulating images, but the
interface only speaks maths. So a number of people have written Windows
and Mac programs that provide a nice, easy to use front end for it. Some
are reasonably priced, and certainly for Windows there are also good free
versions, such as Hugin (which I wrote about on About Photography last
year.)
PTLens is one such, simplifying things even more by concentrating on just
one aspect of the many things PT can do. As you can see from the web site
it is really very simple in use.
The situation got muddier a few years back when a large corporation was
granted a US Patent on things that apparently included much prior work, by
Dersch and I understand others, and tried to block the distribution of PT.
However the software has remained available although they forced Dersch to
remove it from his own site at least for a while. I've not kept up with
the state of play on this. It happened with the Ambrotype too.
Most of my information comes not from magazines, but from lists like this
one, and various web sites dealing with photography. I often come across
things I've forgotten on my own pages!
Regards
Peter Marshall
Photography Guide at About http://photography.about.com/
email: photography.guide@about.com
_________________________________________________________________
London's Industrial Heritage: http://petermarshallphotos.co.uk/
The Buildings of London etc: http://londonphotographs.co.uk/
My London Diary http://mylondondiary.co.uk/
and elsewhere......
> Peter, you say
>
> > PTLens does make a fairly dramatic difference on images from my Canon
> > Digital Ixus. I use it as a plugin on PS7. It has a number of
> > correction
> > factors for different focal lengths and uses the appropriate one based
>
> Could you please give an idea of the kind of correction you would use
> if for? I think of my problem as being unusual because of the nature of
> the project and the close quarters... But it's not?
>
> Also, what is the "Panorama Tools" you mention in your last
> sentence... Is that the "P" in PTL? Or?
>
>
> meanwhile, thanks very much for the info...It's all something I've
> never heard of and need to study. (I guess you have to read computer
> magazines?)
>
>
> Judy
>
> On Tue, 3 Aug 2004, Peter Marshall wrote:
> > I've not used Debarrelizer, but you can also do this using the PTLens
> > plugin, which is basically a free front end for this aspect of
> > Panorama
> > Tools (also free.)
> > http://epaperpress.com/ptlens/
> >
> > Unfortunately PTLens is Windows only, but there is a similar program,
> > LensFix, for Mac, but this isn't free, and I think Debarrelizer is
> > cheaper.
> > http://www.kekus.com/plugin/index.html
> >
> > You can use PTLens to correct distortion on any lens, and you can
> > either
> > create your own correction factors for new lenses or send some test
> > images
> > to the author who will do it for free to add to those he already
> > distributes. I wrote about it in a feature a few weeks ago, the
> > relevant
> > page is:
> >
> > http://photography.about.com/od/digitalcameras/a/a062504_5.htm
> >
> > and on the previous page I also tell you how you can spend a few
> > hundred
> > dollars on stuff that does much the same thing but only for specific
> > cameras and lenses.
> >
> > PTLens does make a fairly dramatic difference on images from my Canon
> > Digital Ixus. I use it as a plugin on PS7. It has a number of
> > correction
> > factors for different focal lengths and uses the appropriate one
> > based on
> > the EXIF data.
> >
> > Panorama Tools is really an amazing piece of software by Professor
> > Helmut
> > Dersch, freely available but giving better results than some very
> > expensive solutions.
> >
> >
> >
> > Peter Marshall
> > Photography Guide at About http://photography.about.com/
> > email: photography.guide@about.com
> > _________________________________________________________________
> > London's Industrial Heritage: http://petermarshallphotos.co.uk/
> > The Buildings of London etc: http://londonphotographs.co.uk/
> > My London Diary http://mylondondiary.co.uk/
> > and elsewhere......
> >
>
>
Received on Wed Aug 4 04:09:38 2004
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