Perspective

One of the most interesting features of wide-angle lens is "the capability to stretch perspective". What do I mean by that? I mean that when you look through a wide-angle lens, it seems that the distance between objects has extended. The objects that were not so distant could appear too far away. And the proportion of objects dramatically increases, so the one that close to the camera look enormous, but those, which are father away almost disappear in the distance.
But there is a quirk - it's not a physical thing, but an impression we get. As one of the readers (signed as FL) has noted (and thanks for that):
The connection between focal length and perspective in your explanation is false. The only thing you have done is choosing an arbitrary position in space that the three lines are to intercept at. If this position is not the same position as the camera, it only shows that you have moved. And that is exactly what has changed the perspective, you moving, not the change in focal length. Change in focal length without moving does nothing to the perspective. Moving does a lot to the perspective, also when keeping the same focal length. Perspective and moving is strongly related. Perspective and focal length is not related in any way (other than you might have to move in order to get your arbitrary position inside the frame, which in turn will change perspective).

Viewing angle on the other hand, is related to focal length, but a larger/smaller viewing angle will not change the perspective, not even a bit. Try drawing all three lines from the same point on the base line (where the camera sits) and see for yourself that the perspective does not change, only the viewing angle. Or even better, do this test: Take two pictures, from the same position without moving, one with say 28 mm focal lebngth, the other one with for example 100 mm. Crop the 28 mm image and resize it, so it has the same scale as the 100 mm. Lay them ontop eachother, and voila: The perspective is the same, despite the different focal lengts. You can also google for "focal length perspective myth" and see some examples (for example this one ) without making your own experiment (but experimenting is much more fun). You will also discover, if you examine the pages returned by google, that the exact same thing goes for focal length and DOF (depth of field).
And I have to agree with this comment. In order for the object to fit entirely into the frame - we move and as such change the perspective. So the primary driver of the change is the viewing angle and the fact that we step back or forward to adjust what gets into the frame. Though the final effect and impression is still of the "stretching perspective", which is just an impression. So, when you read my words about "stretching perspective", keep in mind that this applies only to our impression (since we have moved to achieve the desired result).
The effect caused by various focal lengths on the perspective I described in one of the previous articles. But I will try to dive deeper and describe in more details here.
Here is the basic comparison of impression between different types of lenses:

Perspective Stretch
The image shows how different lenses affect the perspective. The wider the angle the shorter the stronger the difference in the sizes of the elements in the photograph. If you look at the point where the green line with the label "wide angle" intersects with the axis, this is a point, which I would call perceptive vanish point for wide angle lens. What do I mean by that? Well, theoretically at this point and beyond (at this distance from the focal plabe) all elements would be represented as a dot or not visible at all. For normal lens (of in reallity) this vanishing point is somewhat farter from the focal plane than for the wide-angle lens — the intersection of the blue line and the axis.
What do those two points mean? They mean that the wide angle lens reduce the actual distance to the vanishing point. Which results that our brain, when judging the distance and sizes of the objects in the photograph, assumes that the distance to the vanishing point is the same as with normal lens (i.e. reality). But this assumption makes it to stretch the perspective recorded in the image to the normal one. This stretch is indicated at the right bottom corner of the picture above with the red ink.