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Re: [OM] I must admit

Subject: Re: [OM] I must admit
From: Jim Nichols <jhnichols@xxxxxxxxxxxxx>
Date: Tue, 9 Feb 2016 15:24:40 -0600
Hi Chuck,

It was too cold for me to go out and be as industrious as you. I settled for a framed painting on the living room wall. Shot square on and centered, it worked pretty well.

Jim Nichols
Tullahoma, TN USA

On 2/9/2016 2:35 PM, Chuck Norcutt wrote:
I wasn't aware that Picture Window Pro was now doing that. I used to use PTLens by ePaperPress. It's a Photoshop plug-in that has distortion profiles for lots of lenses which are provided by users of the software. I've provided profiles for most of my own lenses which includes a lot of OM Zuikos as well as Canon mount Tokinas and Tamrons.

The procedure involves photographing an architectural subject with very square lines. The author was pleased with my test shots since he said they were very easy to work with. I chose a late 1950s 3-story grammar school building whose exterior was largely straight aluminum beams encompassing large windows and colored aluminum panels separating the glass. Vertical and horizontal lines all over the place and very square. He then does measurements from the images to develop a distortion profile for the lens and at various focal lengths for zooms.

PTLens is still available <http://epaperpress.com/ptlens/index.html> You can get a free trial version that will correct 10 images. After that you need to buy a $25 license. Here's an interesting comparison between PTLens and Photoshop lens correction. PTLens is superior in some cases. <http://epaperpress.com/ptlens/lensCorrect.html>

Chuck Norcutt


On 2/9/2016 11:15 AM, Jim Nichols wrote:
Thanks, Moose.  I use Picture Window Pro 7.0 as my image editor.  I dug
into the documentation and found that I can take a sample image made
with a given lens, pull a broken line to the edge that I want to
straighten, hit compute, and it will calculate polynomial corrections to
remove the barrel distortion.  This can then be saved for that lens, and
recalled any time the correction is required.

With a few iterations, I got a perfect match to the in-camera JPG
image.  While not an automatic solution, it only adds one step to my
work flow, and only for problem images.

It will even work with fisheye lenses.

Jim Nichols
Tullahoma, TN USA

On 2/9/2016 3:14 AM, Moose wrote:
On 2/8/2016 9:58 PM, Jim Nichols wrote:
If I may join this thread, I must admit that I learned something new
(to me) today.  I have noticed that, starting with a RAW file, I
sometimes get some barrel distortion when capturing horizontal lines
with the X-E1 and 35/2 lens.  When I look at the camera-produced JPG,
most of the distortion is missing.  I concluded from this that the
lens corrections are missing from the RAW files.

Is this correct?

Yep, it's a RAW file, and thus not processed to correct the linear
distortion, or anything else. The information to make the corrections
is in the RAW file. The RAW converter makes the correction as part of
the conversion from RAW to general purpose formats.

In the case of µ4/3 RAW files, Oly Viewer 3 and ACR/LR automatically
make the corrections, and in fact, that can't be turned off. So their
outputs exactly match the JPEGs that were corrected in camera. DxO
Optics Pro doesn't use the manufacturers' settings, but uses their
own, from their own testing, and one may turn correction on and off.
In limited testing, their corrections were better than the defaults in
ACR.

I know exactly nothing about Fuji RAW files and conversion, but there
is undoubtedly a way to make distortion correction a part of the
conversion process.

Straight Lines Moose



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