quixdraw wrote:
Have no experience with the others, but have the Nikon. Not a pro lens, but small & light. Does a good job. If the landscape includes trees at the edges, the low end slants them in a bit.
The slanting is commonly observed with many wide angle lenses and is related to perspective. If you have your camera level and take a shot of a set of vertical lines going horizontally across your field of view, the ones on the outside will be curved. Usually you're standing on the ground and the vertical lines are stretching upwards at the edges so you're basically looking up at the top corners and the lines will curve in. The effect will be pronounced if you look upward slightly with your camera. You are seeing more of the upper sections of the vertical lines which are curving inward. If you were on a tall ladder and looking downward slightly with your camera the lines would curve inward at the bottom corners. That would make the lines slant outward a bit instead of inward.
Some lenses can distort the image to compensate for that perspective, but doing so is a distortion, not an accurate representation of the image.
Shift-tilt lenses can introduce some controlled distortion that way.