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Equation for Beam Angle

Discussion in 'Lighting and Electrics' started by Tyler, Dec 8, 2008.

  1. Tyler

    Tyler Member

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    000000000000
    0000000000000000000000
     
    Last edited: Nov 9, 2009
  2. icewolf08

    icewolf08 CBMod CB Mods

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    In is simple trig:
    [​IMG]
    In this image, A is the throw, B is 1/2 the field diameter, and C is the beam edge or hypotenuse of the right triangle created by A and B. Lets call the beam angle X. Most of these calculations require a good scientific calculator.

    So you know A and B. To get beam angle: X=2*atan(B/A)
    NOTE: atan = Arc Tangent or inverse tangent

    So you know the beam angle (X) and B. To get throw: A=B/tan(X/2)

    So you know beam angle (X) and A. To get Beam width: A*tan(x/2)
     
    Cheever and (deleted member) like this.
  3. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

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    Nicely done, Alex. [user]Tyler[/user], for more, see the CB Collaborative Article: http://www.controlbooth.com/forums/collaborative-articles/7664-mathematical-formulas-lighting.html.

    One caution: Don't get "beam angle," "field angle," "beam," and "field" confused. When referring to a 26° ERS, the number is referring to the fixture's field angle. Usually, when planning a wash from multiple fixtures, one wants to overlap fields, but not beams. Softening by "running the barrel" or adding a light frost (X114, X119, X132) covers a multitude of sins/errors in judgment.:)

    Do they still print trig. tables in the back of textbooks?
    Edit: Backstage Handbook, Third Edition (Blue Cover). Paul Carter. Broadway Press, 1994, page 226.
     
    Last edited by a moderator: May 30, 2014
  4. gafftaper

    gafftaper Senior Team Senior Team Fight Leukemia

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    FYI 1994 is the most "current" edition of the Backstage Handbook. Maybe if we are lucky 2009 will bring us a 15 year update. :rolleyes:
     
    Last edited by a moderator: May 30, 2014
  5. CavezziMagnum

    CavezziMagnum Member

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    From your keyboard to whatever you believe in's ears.
     
  6. waynehoskins

    waynehoskins Active Member

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    Wow, how time flies. I got mine when I started college in '99 and the book was a mere 5 years old .. that can't have been nearly 10 years ago now, can it?
     
  7. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

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    What in the current (1994) edition of Backstage Handbook is out-of-date? What additions do you feel necessary?
     

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