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 Purpose of knife-edge in Schlieren (optics)

  1. Dec 18, 2016 #1
    I wanted to know what the purpose of the knife-edge in Schlieren optics is, but can't think of a suitable answer.
    Is it only to reduce the intensity of light equally?
    Thanks!
     
  2. jcsd
  3. Dec 18, 2016 #2

    A.T.

    User Avatar
    Science Advisor
    Gold Member

    Not equally but selectively.
     
  4. Dec 18, 2016 #3
    Most of the light will pass through places where the density variations are small and will focus to a tiny diffraction limited spot at the focus. You are not interested in this light. It is boring. The light that passed through interesting density variations is perturbed. It no longer has a nice flat wave front and it won't make a tight little spot at the focus. You can greatly enhance the contribution of the interesting light if you block the boring light. What you need is a little absorbing dot about the size of the diffraction limited spot placed at the focus. However that is hard to make and hard to place in three dimensions. Instead, for the cost of about half of the interesting light you can much more easily block the boring light by inserting a knife edge at the focus. It only has to be placed correctly in two dimensions, and one of those, the focus dimension, is fairly forgiving.
     
  5. Dec 18, 2016 #4
    Yes, your answers are logical, well-thought and I think correct. Thank you very much, guys!!
    Replusz
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Purpose of knife-edge in Schlieren (optics)
  1. Throwing Knife (Replies: 5)

Loading...