As you asked so nicely MRCDH I guess I can wade in and see what I can stir up. 1st up a little light reading for you to do that range from the technical to the more photogenic. The following should acquaint you with the subject.
https://en.wikipedia.org/wiki/Perspective_distortion_%28photography%29 A Guide to Perspective Distortion Review - Introduction | PentaxForums.com Reviews Portrait Lenses, Beauty and Perspective - digital Artform Perspective Control in Images - Focal Length or Distance? (a tutorial) -- General Photography Talk in photography-on-the.net forums
The most important thing to realize here is it’s all based on the perspective of where your camera is looking and the distances between the various objects in the field of view. When you understand perspective and perspective distortion you understand why a normal lens is called a normal lens and why some photographers prefer certain focal lengths for portrait photography. It really starts become simple and obvious when you understand it.
The reason it is so important with this particular lens is because as you get farther from normal (and this lens is just about as far from normal as you can get in the wide direction) the more apparent perspective distortion becomes. This lens is so wide that the simple rules of just don’t do “X” almost don’t apply. It is imperative that you always are totally aware of the distances to all your subjects and the angle your cameras is at and how these angles change these distances.
As I am limited to the photos I can post to this forum (as in I can’t post anymore photos) I am limited to showing you examples from my Flickr site. This should be more than enough photos to get your eyes blurry. All of these photos were taken at 8 mm and if I remember correctly I made no effort to correct Keystone distortion. If you hover your mouse over these photos you should see a double ended line up in the right corner. If you click on that the photos should size down and you should be able to see the other information that Flickr will give you.
https://www.flickr.com/photos/dazt/24149779562/in/datetaken/lightbox/
In this photo you can see there is a little bit of convergence with some of the objects near the edge of the frame. But as this room was actually around it is very difficult for me to determine where the straight lines were.
https://www.flickr.com/photos/dazt/24149775042/in/datetaken/lightbox/
Again another round room but easier to see the straight lines. This is over 110° wide.
https://www.flickr.com/photos/dazt/20838537531/in/datetaken/lightbox/
Here is readily apparent the convergent effect.
https://www.flickr.com/photos/dazt/16599768277/in/datetaken/lightbox/
Here even though there are people relatively close to the edge of the frame they look for the most part normal. The reason is the importance of distance. If the people are too close to the camera and at the edge of the frame different parts of them will be significantly different distances and will generate the distortions. The person furthest away is actually the tallest at over 6 feet the person closest is only about 5’ 6”. More on that later.
https://www.flickr.com/photos/dazt/14238693063/in/datetaken/lightbox/
Another example of the convergence of the distance.
https://www.flickr.com/photos/dazt/13673991663/in/datetaken/lightbox/
Here I can make my shadow look much longer than it really is.
https://www.flickr.com/photos/dazt/13673997384/in/datetaken/lightbox/
More people at the edge of the frame. There is some distortion to the person closest to the camera but almost none in the distance.
https://www.flickr.com/photos/dazt/13673873694/in/datetaken/lightbox/
Technically the ramp is keyhole distorted here. In this case the distortion helps to increase the apparent size of the airplane.
https://www.flickr.com/photos/dazt/13673943844/in/datetaken/lightbox/
Here the people are too close to the camera and it does generate some unpleasant distortions. This is mostly apparent in people since we are very conscience of what people are supposed to look like. In this case it was unavoidable as there is no place else for me to go in the relatively small cockpit of a C-17. Without a lens as wide as this I would not have been able to of captured the cockpit as a whole.
https://www.flickr.com/photos/dazt/9533615204/in/datetaken/lightbox/
This view looks relatively normal. This is deceiving as if you are actually standing here you would’ve naturally have turned your head slightly one direction to the other to looked on the 2 different paths. They are over 90° apart. As you can see though the trees all look like they’re standing relatively straight up.
https://www.flickr.com/photos/dazt/8254380334/in/datetaken/lightbox/
Here by going portrait orientation I was able to keep the buildings in view with a minimum of keyhole distortion.
https://www.flickr.com/photos/dazt/8254374426/in/datetaken/lightbox/
Here going back to horizontal orientation and keeping the camera close to horizontal (it still pointed up slightly) I was again able to keep the buildings relatively square and capture both edges of the fountain.
https://www.flickr.com/photos/dazt/8253293835/in/datetaken/lightbox/
By moving up to the 2nd floor and standing at the edge of the balcony I was able to keep everything square and capture the entire room.
https://www.flickr.com/photos/dazt/8254112398/in/datetaken/lightbox/
Even though everything is relatively square here (except that which was naturally damaged in the storm) both the clouds and the wave lines on the sand still generate convergent lines.
https://www.flickr.com/photos/dazt/7483619908/in/datetaken/lightbox/
Here the perspective distortion makes the plane look like a tunnel.
https://www.flickr.com/photos/dazt/5905926177/in/datetaken/lightbox/
By cropping out the top and the bottom of the photo gives you a more panoramic feel and essentially eliminates the perspective distortion.
https://www.flickr.com/photos/dazt/5569714413/in/datetaken/lightbox/
Here the perspective distortion makes the slight path loop look much greater than it really is.
https://www.flickr.com/photos/dazt/5570259904/in/datetaken/lightbox/
Here you don’t really see the perspective distortion unless you realize that the flowers are all planted in a perfect square.
https://www.flickr.com/photos/dazt/5167457490/in/datetaken/lightbox/
Here again I kept the camera perfectly perpendicular to all of the vertical structures. The perspective distortion is in the shadows and the sun light. One of these days I intend to make better use of this effect I just haven’t found a subject better than this yet.
All of the above should give you enough to chew on with this new lens for a while. Remember pick your perspective 1st, then choose your framing for what subject matter you wish to include, this then will dictate your field-of-view angle and that will let you pick the lens length to use.
DAZ