Can you explain exactly how a level will resolve tilted horizons or tilted landscapes? I'm not really comprehending it in my head. It appears to me that a level camera is irrelevant to a level photograph...
Thanks! (I'm sure this will click soon enough)
Mark
Used to correct roll, clockwise or counter-clockwise, a level helps get the upper and lower film edges into paralel with the perfect theoretical horizon.
Used to correct pitch, getting the film plane absolutely vertical, gets vertical subjects, like trees, buildings, people, etc... to stand up straight.
Yaw in relation to the subject is one wild card here that can mess with a perfectly level camera.
In the middle of the ocean it doesn't matter because the horizon, regardless of what the flat earthers say

, is simply limited by the curve of the earth it is essentially the same distance from the camera regardless of the direction you look, this is as close as we get to a perfect theoretical horizon.
On land the distance to the horizon can be limited by any number of things, as the camera is swung left or right only a horizon line exactly half way between top and bottom of the frame will remain parallel to the top and bottom on the film. Horizontal lines above and below the middle will tilt more and more as yaw increases, this effect also gets more pronounced the further you get toward the edges of the frame. This effect is easy to see if you take a shot of a building straight across a street, then swing the whole camera left or right for a second shot.