Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

To converge and to diverge

  1. Aug 9, 2004 #1
    Hello... I need some help... :-p

    Can I use concave mirrors to reflect sunlight?

    If I look very close at a mistletoe, Why can I view the entire room upside down? Is mistletoe a mirror of sort?

    And, is it true that there is a special eyeglass that is as effective as an ordinary eyeglass in a way that instead of using lenses, the special eyeglass has numerous punholes which allow light to pass so the user can see object clearly?
  2. jcsd
  3. Aug 9, 2004 #2
    i can answer the first one easily,
    yes you can use a concave mirror to relfect sunlight. any mirror in fact should do this.

    is mistletoe a shine leaf plant? if it is thats perfectly possible
  4. Aug 9, 2004 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Yes a pin hole can provide a relatively clear image even if your vision is poor. A sheet with many pin holes can nearly act like glasses BUT the intensity of the image is very low, so it is not nearly as good a that provided by a properly fit pair of glasses.

    The reason that this works is that most vision problems are caused by the lens in you eye not focusing an image in the correct plane (on your retina) The reason it does not work correctly is due to large scale errors in the shape of the lens. If you restrict the incident light to a pin hole only a very small section of your lens effects the light, thus the errors induced by your lens are much smaller.

    A pin hole is a very effective lens of its own, the original camera, called a camera obscura, was simply a pin hole in the wall of a dark room, an image of the outside sun lit street appeared on the opposite wall.

    One could argue that since the light from a pin hole encounters such a small area of your eye that the eye does not act like a lens at all, you are simply seeing the camera obscura image on your retina.

    When more pin holes are used the image brightens, but it is still not as bright as a properly fit set of glasses.
  5. Aug 10, 2004 #4
    Hi Erienion! For your mistletoe... yes. =)
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: To converge and to diverge
  1. Meaning of Divergence (Replies: 7)