system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:What, exactly, is tilt shift and why does it look so different?

It looks so groovy, but I just can't understand why it's so different looking.
gpt
Lenses bend light to focus it on the sensor of the camera, so it captures the image. Tilting and shifting the lens distorts how the light hits the sensor, creating those groovy shots.  
  
Shifting the lens moves the center point of the lens from the center of the sensor. While the lens only moves around a centimeter or two, it causes a much more dramatic shift in the image, as if you took several steps in the shifted direction. It is very useful for shooting buildings, because you don't need to tilt your camera to capture the whole building (doing so distorts the perspective, making the top narrower than the bottom).  
  
Tilting the lens is a bit more complicated, because it angles the plane of focus. Normally the lens focuses a plane parallel to the camera sensor. But when the lens is tilted, one part is closer to the sensor than the other. The light's path through the lens remains unchanged, but the way its cast onto the sensor changes. Like with shifting, a small change in lens angle results in a much larger change in focal plane angle. You can tilt the lens to increase or decrease the effective focal plane. If you have an image with flowers in the foreground and mountains in the back, it would be hard to focus on both. But you can tilt the lens to create a focus plane that encompasses the whole scene with ease.  
  
On the other hand, you can tilt the lens in the other direction, reducing the focal plane to a razor's edge. This causes objects slightly in front and behind the plane of focus (which wouldn't normally be too blurry) to appear much more out of focus, which gives the impression that you're photographing a very small model. The farther away from the sensor you focus, the larger the area of focus will be. A small model of a city may be ~1 foot from the lens, while an actual city will be dozens or hundreds of feet. By reducing the depth of the focal range, it appears similar to moving the sensor closer to the subject.