Thread: Perspective: How?

It may sound like an utterly rudimentary question, but Why do things look smaller from farther away? What mechanism is at work that makes this so? I found one explanation that stated, "because the reflected light from the objects occupies less space on your retina," but that's no better than saying, "they look smaller because they appear smaller." I understand the theory of perspective, how to represent it, but I'm very curious to know ...

What is the mechanism that causes objects in perspective to appear larger or smaller?

I think it all boils down to resolution and the brains way of dealing with the lack of it. Your mind will often fill in the blanks in detail with what it knows. Just like the sides of your vision are constructed from fragments of what it knew was there. Not really sure this is a Physics question. The true test would be to see if a machine sees a series of objects as being the same object from a distance. That then still goes back to lack of resolution. The machine would match points and come to a conclusion of what the object was. Less points of information equals less accuracy.

Our eyes are very powerful, yet still have limits on resolution. Our brains make up the rest.

The ratio of the height of an object to its distance away is proportional to the height of the image on your retina and its distance from your pupil:

Code:

ObjectHeight/ObjectDistance = ImageHeight/ImageDistance

Solving for ImageHeight:
ImageHeight = ObjectHeight x ImageDistance / ObjectDistance

The height of the object is fixed, as is the distance from your retina to your pupil, so ObjectHeight x ImageDistance is constant:

Code:

ImageHeight = k / ObjectDistance

Therefore, the height of the image on your retina is inversely proportional to the object's distance away. As ObjectDistance increases, ImageHeight decreases.


At the lowest level, the premise to this argument comes from Euclidean Geometry, which I consider to be fundamental (ie the way that reality corresponds to Euclidean Geometry has no fundamental cause that I know of).

G' Day Pete!

Yes. Any object within the fixed area (retina) of the scene that you are viewing will subtend a smaller angle on your retina when it is further away within the scene.

If things didn't appear that way we would constantly be running into them.
Ouch!