Why farther objects appears smaller?

  1. Please, I must have some misunderstanding ,why I see farther objects smaller although there are reflected photons??!!!
  2. jcsd
  3. Doc Al

    Staff: Mentor

    Because they subtend a smaller angle.
  4. I don't understand I have a thread about angles but I can't clarify my idea and what subtended angle... Please see my post about light ..Thanks
  5. HallsofIvy

    HallsofIvy 41,265
    Staff Emeritus
    Science Advisor

    Imagine two lines going from your eyes to a distant hill, one to the base of the hill, the other to the top of the hill. Trees of the same height along the way will take a greater part of that angle as they are closer to you because the angle opens up farther away from you. Since they all project to you eye along those lines, the closer ones will appear larger.
  6. It is also necessary to know how the eye works: it has a lens with adjustable curvature. When we try to observe object, the curvature is automaticly set to focus all rays coming from the same point to the same point on the retina (the back of the eye with light detecting cells). So all light from one point is focused to one point. All light from another point will be focused to another point. If the angle between source points is greater, then they will focus further apart. So the apparent size of the object depends on the angle between it's most distant points, which decreases with distance.
  7. jk4

    jk4 0

    things "appear" smaller from far away because of what Lojzek said, it's the curvature of the eye. If your eyes were flat then you would see something to be the same size 100ft away as you would right in front of you, which wouldn't work very well.

    look at my attatched image. and I appologize for my poor drawing skills.
    Anyway, you'll see that a curved eye or lens creates an angle and you see everything within it, but we see in 2D because, if you look at the top image and trace the lines backwards, you'll see that everything fits into the same area on the eye. So, things farther away appear smaller than if you were to move them closer because they would take up more room in your "field of vision".
    if our eyes were flat resembling the bottom image (and you only had 1 eye) you would have literally zero depth perception, and couldn't even tell if something was moving closer or farther away. Everything would appear zoomed in very close.

    Attached Files:

    Last edited by a moderator: Apr 8, 2008
  8. I don't understand why the properties of the human eye were mentioned here when it's also true for a photograph. Suppose a photograph shows two circles side by side and they appear to have the same diameter -- however the circle on the left is the moon at a distance of about 380,000 km, and the circle on the right is a pea at a distance of about 2 m. I thought Doc Al's answer said it all (although I didn't know about that nice word "subtend").
  9. The photograph,the eye,......How and when far objects appears as near ones without respect to distance?!
    that's all...
  10. Doc Al

    Staff: Mentor

    Have you not been reading the responses? What don't you understand?
  11. Yes I read and understood,my question is can we make something that recognizes every thing at certain image size irrespectable to how far are objects..? thanks.......
  12. Doc Al

    Staff: Mentor

    What do you mean by "make something"? Are you concerned with a mathematical issue? A physical issue?

    If two objects subtend the same angle, they will "look" the same size. Where's the mystery?
  13. My guess is:

    Because your eyes can only absorb so many photons. The closer you are to the object the more photons from the object will hit the rods in your eyes, making the object appear bigger.
  14. cristo

    cristo 8,387
    Staff Emeritus
    Science Advisor

    Have you read the other answers given higher up in the thread?
  15. russ_watters

    Staff: Mentor

    For that, I use a telescope, a camera, and a printer.
  16. Pithy.

    Did I mention that you are one of my hero's Doc?

    OP. Smaller angles mean less photons. It's the reason that looking at the night sky and seeing a million suns far off doesn't instantly blind and incinerate you as seeing the same million suns as close say as ours.....

    To make something that would recognize something regardless of distance as you intimated. For example recognizing an enemy spacecraft at 30 miles or 30,000 miles is a question of resolution. If you can scan the 30 mile craft with a million points and recognize the same outline with one thousand points then the answer is yes. (I know I'm ignoring other occluding factors like say, atmosphere, debris, moisture, temperature etc. but this is a ballpark kinda answer)
  17. russ_watters

    Staff: Mentor

    While generally true (exception: lasers), this has nothing whatsoever to do with why objects further away appear smaller.
  18. I'm not sure about how to answer your question but i have a feeling the previous post has dont just that but have you noticed sometimes from the same vantage point looking at the same thing on different days the object can look slightly bigger or closer or smaller and further away. From my balcony on some days the buildings in the distance seem closer than normal, maybe has something to do with the atmosphere or because im using my binoculars im not sure lol but seriously sometimes they do appear closer. anyone shed any light on this?? perhaps its something to do with my eyes??
  19. Sorry Russ. You are absolutely right. Put the cart before the horse I did.

    I was considering less reflected photons, and angle subtended by sources, not the general solution.

    (sign on laser exhibit: Do not peer into barrel of laser with remaining eye.)
  20. Why does the moon look bigger some times when it first comes up over the horizon?
  21. (random guess) As the photons from the moon "fly" over the earth, the earths gravity pulls more photons to the earth's surface, and to your eyes .. making the object appear bigger.
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