1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I'm new to optics: need help on lens please!

  1. Dec 16, 2008 #1
    Hi there,

    I found myself stuck to a simple question really. Trying to find a solution on my own doesn't guarantee a success. Therefore I would appreciate if any of you can offer me helps to solve the following questions.

    1. how big a image a lens can see? You see, when you put the image at the focus of the lens, you get a collimated beam behind the lens, which is then focussed onto a ccd by another lens. Normally, I think this is determined by NA. I did some calculation and found that the spot size is much less than what the lens see. So, how can I know how big an area a lens can see. (given its focal length)

    2. this is a related questio to question 1: how can I completely fill ccd? how to determine the focal length of the lenses necessary to fill completely the ccd area.


    many thanks,
    Almost
     
  2. jcsd
  3. Dec 16, 2008 #2

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    It's bit more complicated than that - you need to calculate the rays for the edge of the field not just the centre.
    A simple result for a camera type lens is that FOV = 2 arctan (x / (2 f))
    where x=diagonal length of the ccd and f is the focal length.
    This gives you the angle in degrees that the lens will image.

    If you are trying to build a close-up 1:1 or magnifing imager it's a little different.
     
  4. Jan 16, 2009 #3
    I have a more or less related question. Can one focus an object on the slit of a spectrometer by positionning the object close to the lens (<focal length) and slit at infinity (~150m)?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook