Equation for Beam Angle

[Tyler]

0000000000000000000000

[icewolf08]

In is simple trig:

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.

Originally Posted by Tyler

beam angle when I know the throw distance and beam width

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

Originally Posted by Tyler

throw distance when I know the beam width and beam angle

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

Originally Posted by Tyler

beam width when I know the beam angle and throw distance

So you know beam angle (X) and A. To get Beam width: A*tan(x/2)

[derekleffew]

Nicely done, Alex. Tyler, for more, see the CB Collaborative Article: http://www.controlbooth.com/forums/c...-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.

Originally Posted by icewolf08

...Most of these calculations require a good scientific calculator. ...

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.

[gafftaper]

Originally Posted by derekleffew

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.

FYI 1994 is the most "current" edition of the Backstage Handbook. Maybe if we are lucky 2009 will bring us a 15 year update.

[CavezziMagnum]

Originally Posted by gafftaper

FYI 1994 is the most "current" edition of the Backstage Handbook. Maybe if we are lucky 2009 will bring us a 15 year update.

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

[waynehoskins]

Originally Posted by gafftaper

FYI 1994 is the most "current" edition of the Backstage Handbook. Maybe if we are lucky 2009 will bring us a 15 year update.

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?

[derekleffew]

Originally Posted by gafftaper

...Maybe if we are lucky 2009 will bring us a 15 year update.

What in the current (1994) edition of Backstage Handbook is out-of-date?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