# How come things shrink?

#### Lars Laborious

If someone paints a realsize picture of a person, then walks 100 yards to where you stand and hands you this painting, the painted person is of course still the same size as the real person. But if photons bring you a picture of the same person (i.e. seeing) still standing 100 yards away, the picture shrinks. What happens here?

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#### Doc Al

Mentor
Perhaps I don't understand your question, but are you asking why things appear smaller as they get further away? Because they subtend a smaller angle. Our brains are able to adjust for familiar objects of known size: We "know" that those people across the park aren't really 1 inch tall as they might appear.

But our perspective can be fooled, since our assumptions of relative size are based on our experience and environmental cues. How about this: http://psylux.psych.tu-dresden.de/i1/kaw/diverses Material/www.illusionworks.com/html/ames_room.html

#### Lars Laborious

Yes, you understood me right. But what exactly happens when you subtend a smaller angle? Does the photons gather data about the space between me and the person 100 yards away, so that visual system can shrink the image proparly?

#### Gokul43201

Staff Emeritus
Gold Member
No, it's just that your line of sight sweeps through a smaller angle to cover an object that has moved far away, and it is this angle (outside of any process borrowing from experience) which is our perception of "size".

#### Janus

Staff Emeritus
Gold Member
Lars Laborious said:
Yes, you understood me right. But what exactly happens when you subtend a smaller angle? Does the photons gather data about the space between me and the person 100 yards away, so that visual system can shrink the image proparly?
Check out the attached image. It show how the eye images two objects of the same size at different distances. Note that the image projected on the retina for the furthest object is smaller that the for the closer object and that is because the angle is formed is smaller.

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#### Lars Laborious

Janus said:
Check out the attached image. It show how the eye images two objects of the same size at different distances. Note that the image projected on the retina for the furthest object is smaller that the for the closer object and that is because the angle is formed is smaller.
Thanks! Just what I needed.

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