Why do things look smaller off in the distance?

Factual Questions
1

I’ve tried to figure this out. You don’t get as much light I know, but shouldn’t they look dimmer instead of smaller?
Do the eyes just focus the light into a smaller area to keep it bright? If so come you can see things at multiple distances which would seem to need multiple focus levels at once?

It’s a real head scratcher.

2

Well if you figure out the angles, I think you’ll understand.

Say that straight in front of you is zero. Well a wall that is 10 feet from you and 10 feet wide (viewed face on) will cover 53 degrees of horizontal vision.

2 X atan(5 / 10) = 53 degrees

(If you can just mentally a draw a line from the “eye” to the edges of the wall)



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eye ----------|
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If you place the wall twice as far back, it will cover a smaller degree of your vision.

2 X atan( 5 / 20 ) = 28 degrees



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eye ----------|----------|
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A wall that is farther away covers a smaller degree of your vision, and thus it appears smaller.

3

Annoying addition to get past lame posting filter

4

If I understand your question correctly, the eye doesn’t need to focus in stages when gazing into the distance. Like a 35mm SLR lens, the muscles of the eye can move the lens of the eye (plus control the iris - the aperature) to put the focus at infinty. This, in effect, gives the eye a large depth of field in which all objects will be in focus.

A better question is how does any lens do this? All the optics I’ve studied (the basics plus compound lenses) never addresses this. Instead, the focus is treated as always treated as being one point. Now, that’s a head-sctratcher!

  • Jinx
5

If I understand your question correctly, the eye doesn’t need to focus in stages when gazing into the distance. Like a 35mm SLR lens, the muscles of the eye can move the lens of the eye (plus control the iris - the aperature) to put the focus at infinty. This, in effect, gives the eye a large depth of field in which all objects will be in focus.

A better question is how does any lens do this? All the optics I’ve studied (the basics plus compound lenses) never addresses this. Instead, the focus is always treated as being one point. Now, that’s a head-sctratcher! - Jinx

6

Because your field of vision is shaped like a cone.

7

teehee - as soon as I saw the question I thought of the same classic Father Ted episode too

8

Trying to answer the original question as intuitively as possible… your field of view covers a fixed angle. As you look further away, this cone spreads out to cover a wider area of view. This area still has to be focused onto the same-size retina, so obviously the image of a given object will take up proportionally less of your retina if it is 100 yards away than if it is 1 yard away.

9

Jinx, look for the term circle of confusion. It will help put the physics of focus in focus.

Obligatory WikPedia discussion.

10

I think I understand. What you’re saying is we see size measured in degrees in our vision. Expand the the circle (looking further out) the degrees have to get larger with the circle, and objects relative to new measurement units, are smaller.

Cool thanks everyone.

11

Well, consider the alternative. Suppose you’re looking up at the moon, and instead of being the size of a quarter, it’s actual size, like it’s right up against your nose . . . only dimmer. :eek:

12

I can come up with worse. Think the worst thing you ever walked in on only zoomed up close. :eek: