Originally posted by y0chang I think people are getting lens distortion mixed up with perspective distortion. Lens distortion is when the lens makes lines curved when they are straight. Barrel, pincushion, and mustache distortion are examples of this. The first two are easily corrected in LR, but you lose corner resolution when you stretch out the images and the more you stretch it out the more resolution you lose. The most extreme example of barrel distortion is a fisheye lens. The DA 15 has a mild but non-linear lens distortion characteristic. you can see the corners curve more than the center. Perspective distortion is when depending on your angle of shot, things are distorted in size due to the field of view of the lens. Wide angle lens push the background away and bring the foreground closer. This makes dramatic diagonal lines in many compositions. The DA 15 is a wide angle but it is not as wide as a 10mm rectangular lens. You can still get dramatic angles depending on how close you get to your foreground subject.
To me this just a question on how you want to project the image into the sensor plane.
As long as the projection is not the same as our eyes have naturally and our brain intepret, this will look un-natural, distorted.
Even if you choose a rectilinear projection, a human on the border of the picture will look distorted and quite unatural... it might look more natural indeed on a fisheyes projection even through the lines are curved. But say if we speak of buildings and architecture, maybre a rectilinear lense is better because we think that the building should have straight lines, like in reality. In both cases, this is an artistic choice.
For moderate WA, like a 35mm on FF, a rectilinear look quite natural for building and so own and look quite good still on other objects if they are not near. For quite extreme WA, or UWA, this is another story and would be a case by case basis and I can assure you can improve the image by playing with the projection used, even if you come from a perfect rectilinear lense. That's actually why the options are there in your post processing software... Not just to correct lenses.