Whether an object done in perspective will give the best demonstration1 when viewed from the location where its viewpoint was taken.

If you want to depict something as being nearby that will produce the same effect that natural things do, it will be impossible for your perspective not to appear faulty, with all the deceptive demonstrations and discordant proportions that could be2 imagined in a sorry work, unless the person viewing this perspective positions himself, and his viewpoint,3 at the same distance, height, and straightness of eye, or better, at the same point at which you were situated when making this perspective — so that you would need to make a window the size of your face, or better, a hole through which to regard this work.  And without any doubt,4 if you do so, this work of yours, being well accompanied by shadows and lights, will make the same effect that the natural makes, and you will not be able to persuade yourself that these things are painted.  Otherwise do not get involved with it, unless you start by taking your viewpoint from at least twenty times as far away as is the greatest width or height of the thing you are depicting.  And this will satisfy any viewer of this work located at any point of observation.

If you want to see the proof quickly, get a piece of staff, like a small column, eight times as high as it is wide, like a column without base or capital.  Then mark out forty equal spaces on a flat wall, conformant to the spaces that there would be5 between forty columns like your little column.  Then position6 a thin band of iron four braccia away from the wall, to match up with the middles of these spaces, that has a little round hole at the middle, the size of a large pearl, and to this7 hole, join a light that touches.  Then proceed by putting your column up at each sign on the wall, and indicate the umbra and then the penumbra, and look at them through this hole in the iron.