Focal distance and perspective
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HoppyUK
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Haha! Coffee/keyboard moment! LOL
That's handy little animation, and worth a bit more explanation in the Basics section. When the cat's body is small and almost hidden behind the head, that's shot with a wide-angle lens from close distance. At the other extreme where the cat's body is large, that's shot from greater distance with a long focal length lens. Also note how with the longer lens, there's much less background visible due to the narrower angle of view.
As noted, perspective is purely a function of shooting distance, not focal length. It's just that wider lenses allow you to shoot closer and still include everything, but with more exaggerated perspective. Easy test - shoot with a wide-angle from greater distance and enlarge the centre of the image, and perspective will appear exactly the same as when using a longer lens from that same distance.
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Wot Hoppy sed! Although with some UWAs (and especially with fisheyes), distortions will creep in as well as perspective exaggeration.
(Luckily [well, not luck, more forward thinking!] the table's polyurethane varnished so puke, spirit, almost everything proof!)
(Luckily [well, not luck, more forward thinking!] the table's polyurethane varnished so puke, spirit, almost everything proof!)
HoppyUK
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Distortion is something else though, and all lenses can be prone to it.
It is a lens aberration (fault) and comes in two flavours. Wide-angles tend to suffer from 'barrel' distortion where straight lines near the edges of the frame, such as a wall or roof of a building, are curved outwards. Telephotos tend to suffer more from 'pin-cushion' distortion where straight lines are curved inwards. Zooms with a large focal length range from wide-angle to telephoto usually have both types at either end of the zoom range.
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Wot Hoppy sed II 
The example I like is to take a shot from inside a building looking out through a doorway or open window.
Stand at the same point and take a wide angle and a telephoto shot. If you view both shots but enlarge the wide angle you will see that the perspective is the same.
However if you move closer or further away the view of the outside will change, you will see either more of the outside scene or less.
This can be put to practical use when taking a photo with a "frame" such as a tree or an archway. Move backwards and forwards until the scene through the "frame" is what you want, hiding unwanted elements and getting the composition right. Then change the focal length so that you include as much of the "frame" that you want.
The example I like is to take a shot from inside a building looking out through a doorway or open window.
Stand at the same point and take a wide angle and a telephoto shot. If you view both shots but enlarge the wide angle you will see that the perspective is the same.
However if you move closer or further away the view of the outside will change, you will see either more of the outside scene or less.
This can be put to practical use when taking a photo with a "frame" such as a tree or an archway. Move backwards and forwards until the scene through the "frame" is what you want, hiding unwanted elements and getting the composition right. Then change the focal length so that you include as much of the "frame" that you want.