The image samples are 100% crops of full images. They were shot
with a 1D using the standard curves settings, Matrix 4 (AdobeRGB)
and default sharpening setting. The images were brought into
Photoshop and assigned to AdobeRGB. I then corrected for barrel
distortion/perspective, resized, and converted to sRGB before
few months ago, I had an opportunity to review the new Canon
16-35L super wide-angle zoom lens and make a few comparisons
with the 17-35L.
I have received many emails asking me how well the new 16-35L
compares to the 17-35L in regards to barrel distortion.
tested the older 17-35L and from my analysis, I found severe
distortion at about 5.5-6 % at its widest focal length (17mm).
I decided to test the new 16-35L for distortion as well, at
the following focal lengths: 16mm, 20mm, 24mm, and 35mm
used my new Canon 1D to shoot a grid target.
Then I used an excellent Photoshop plug-in from Helmut Dersch,
Tools, to calculate the amount of distortion compensation
are the results of my tests:
at 16mm: (distortion of ~2.1%)
at 20mm: (distortion of ~1.3%)
at 24mm: (distortion of ~0.7%)
at 35mm: (insignificant)
These results were acquired by taking
a picture of a target at the selected focal lengths and guessing
the distortion levels until the target lines became straight
(free of barrel distortion).
1 (before and after barrel distortion correction) - 1D, f/8,
1/200s, 16-35L at 16mm
2 (before and after barrel distortion correction) - 1D, f/3.2,
8 seconds, 16-35L at 16mm
How to use the free Panorama Tools
Download PanoTools: PC
- Place the file pano12.dll into the same directory as Photoshop.
- Place the file correct.8bf into the Plug-ins folder for 'Filters'.
- Restart Photoshop. You should find the Tools in the Filters
is a screenshot of the Filters submenu:
check "Radial shift" and make sure the other options
are unchecked. Click on Options.
'a' and 'c' to zero for all colors, choose a value for 'b' and
choose 'd' so that d + b = 1. For barrel distortion compensation
'b' must be negative. For the 16-35L at 16mm, use "a =
0", "b = -0.021", "c = 0", and "d
= 0.021" (2.1%) for all colors (red, green and blue).
choose your interpolation method. I recommend Spline
36Pixels for great quality and performance. If you have
time and your files are not too large you could choose
Sinc 256Pixels for the best image quality.
in mind that the above settings are custom made for the 16-35L.
If you want to use the above technique for your own lens, you'll
need to calculate and customize your settings based on your
target grid. When tilting your lens upwards or downwards, you
may have to correct the perspective as well. You can do that
easily using Photoshop.
you image. Select all (Ctrl-A). Edit/Transform/Skew
move your points until lines that should be parallel get parallel.
is an extreme example corrected for barrel distortion (panorama
tools) and perspective (transform/skew):
(April 6th, 2002):
Photographer Dale Kaechler, tested his Sigma 15-30mm f/3.5-4.5
EX Aspherical DG DF zoom lens and calculated the following distortion
settings using the above method.
are his findings:
Sigma at 15mm: distortion of 1.8%
15-30mm Sigma at 20mm: distortion of 0.9%
15-30mm Sigma at 24mm: distorition of 0.3%
15-30mm Sigma at 30mm: insignificant
(before and after barrel distortion correction) Sigma 15-30mm
f/3.5-4.5 @ 15mm
by Jerry Eakes
(November 1st, 2002):
V Christensen tested the D60 with Sigma 17-35 EX for barrel
distortion using PanoTools and found the following:
value to correct at x mm
mm. b d
17mm -0,008 1,008
18mm -0,007 1,007
19mm -0,006 1,006
24mm -0,001 1,001
(0,001 step down
per mm step up)
discuss this tutorial, visit the Canon
digital SLR board. Click here
for a full review of the Canon 16-35L.
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