Quote Originally Posted by Diapositivo View Post
PS It goes without saying that while using small format the vertical line to be taken as measure is to be on the exact centre of the frame.
Actually this shouldn't have been said.

An off-center vertical is actually better because it allows you to judge both tilt (right or left) and pitch (forward or back). A vertical dead center can only help with tilt.

Get one off-center vertical right and all the rest of the verticals will fall in line too.

Going farther, if you get one off-center vertical and one off-center horizontal composed "squarely" in the frame all the rest will follow. At that point only the lines leading away from the camera will converge.

While it is possible to use these concepts on any camera, fixed lenses, that can't be moved left, right, up, or down, force significant compromises in composition and camera placement, generally leading to serious cropping.

Also lens distortion, barrel or pincushion, complicates things too.