Results 1 to 6 of 6

Math Help - Help with a question please?

  1. #1
    Newbie
    Joined
    Jul 2012
    From
    England
    Posts
    2

    Help with a question please?

    Hi all,

    I just joined this Forum to get an answer to a question really, it's not for Collage or Uni or anything just a curiosity really.


    What I'd like to know is.... If an Object is 3 miles away, and this is what complicates things a little (for me at least), it is 3mm wide by 4mm heigh through a pair of Binoculars (15x70).
    What size would the Object be?


    I'm also not 100% sure of the distance so if anyone could help me out with this could you also do the same thing but with the Object at 2 miles and also 4 miles away if possible?


    If anyone can help me with this I'd be really grateful.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Newbie
    Joined
    Jul 2012
    From
    California
    Posts
    5

    Re: Help with a question please?

    well im not sure this is completely possible, im not sure, not saying its not possible... HOWEVER! it is impossible because there are unknown variables, like, how powerful are the binoculars, 200x? more, less?
    Follow Math Help Forum on Facebook and Google+

  3. #3
    MHF Contributor

    Joined
    Apr 2005
    Posts
    15,720
    Thanks
    1475

    Re: Help with a question please?

    Saying the binoculars are "15x70" tells us the diameter of the lens and the focal length of the objective lens but says nothing about the magnification. The magnification is the focal length of the objective lens divided by the focal length of the eyepiece.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor
    Joined
    Oct 2009
    Posts
    5,537
    Thanks
    778

    Re: Help with a question please?

    Quote Originally Posted by HallsofIvy View Post
    Saying the binoculars are "15x70" tells us the diameter of the lens and the focal length of the objective lens but says nothing about the magnification.
    Are you sure? This site says that the first number is the level of magnification and the second one is the diameter of the objective lens.

    Quote Originally Posted by Libertine View Post
    What I'd like to know is.... If an Object is 3 miles away, and this is what complicates things a little (for me at least), it is 3mm wide by 4mm heigh through a pair of Binoculars (15x70).
    What size would the Object be?
    I am not an expert on this, but I think that the question "what size" does not make sense unless one also specified the distance to the object. For example, a coin at the arm's length can have the same size to me as the Moon. Alternatively, one can talk about the angle of view. As long as the objects are small enough, making an object appear n times closer is (approximately) equivalent to increasing the angle of view n times.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Newbie
    Joined
    Jul 2012
    From
    England
    Posts
    2

    Re: Help with a question please?

    Hi,

    MadlySavage and Hallsofivy.

    Emakarov is right,The Binoculars are 15x magnification.
    The object was to far away to see with the naked eye because it would have been 15 times smaller.


    Hi Emakarov.

    I have, the distance from me to the object was 3 miles.
    What I'd like to know is how big would the object be if I were standing right next to it?

    Thanks all for taking the time to have a go.
    Follow Math Help Forum on Facebook and Google+

  6. #6
    MHF Contributor
    Joined
    Oct 2009
    Posts
    5,537
    Thanks
    778

    Re: Help with a question please?

    What I should have said, I am not sure what it means for an object to appear to be 3 x 4 mm through a pair of binoculars. I think the linear size (say, width) can be used in one of the two contexts. Either you say that an object itself has a particular width (this obviously does not depend on the distance from the observer to the object), or you say that an object O₁ at distance d₁ from the observer has the same apparent width as an object O₂ at distance d₂.
    Last edited by emakarov; July 2nd 2012 at 11:29 AM.
    Follow Math Help Forum on Facebook and Google+

Search Tags


/mathhelpforum @mathhelpforum