Sigma 12-24mm II – Discussion on Distortion Correction

Here are a few additional examples illustrating the distortions in the new Sigma 12-24mm lens, and the distortion corrections applied with PTLens.

First, the question has come up of how much of the image is lost around the edges as a result of distortion corrections, and if because of this loss if the field of view would be that much differentfrom a 14mm lens. Well, I though a good example would be to take a 12mm shot, apply the distortion correction, and then compare it against an uncorrected shot with the lens at 14mm.

Sigma 12-24mmII at 12mm - uncorrected and corrected vs 14mm uncorrected

As you can see above, while a little bit of the edges are lost from the correction, there still is a little more field of view than at 14mm. The caveat here is that when lens manufacturers label their lenses, the described focal lengths are usually approximations rather than exact focal lengths. (As one astute reader of my previously posted review noted, Sigma’s patent on this lens says it is actually 12.45mm-23.03mm). So, 14mm on one lens may not be 14mm on another. But hopefully this illustrates that at 12mm you still do get a little extra field of view even after correcting.


Next, here is a comparison of the new lens versus the old lens, with and without distortion corrections applied to both.

New vs old lens at 12mm, with and without distortion corrections

The old lens needs less distortion correction, but I find myself very impressed with how PTLens is able to correct the images without sacrificing too much of the edges.


Finally, there is always a concern that when you push pixels around in software, you will lose a little bit of sharpness. I found this to be true whenever using the Lens Correction filter in Photoshop. It doesn’t destroy the image or anything, but it does degrade it very slightly.

However, with PTLens, I have to say that I was shocked that after applying distortion corrections: I had a very difficult time discerning any significant impact on sharpness. Even the corners seem to hold up well.

Sigma 12-24II at 12mm, uncorrected and corrected

100% crops, upper left corner





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