CHRIS HOWCROFT

Lighting Designer — Production Electrician — Eos Programmer — Philosopher for Hire

VSFX Beam Size Calculator

I made this calculator to help work out how big the image from a vsfx style projector will be on a cyc. It's easy to work out how wide the image will be in the middle of the beam, but it's often useful to know what width you will have at the top and bottom of the cloth so that you can avoid gaps and/or overlaps. This calculator tells you that, and also how much of the total beam is actually hitting the cloth (so you can avoid hanging positions which fill the desired space but with an inefficent amount of the light).

This calculator uses data from the beam spread table and lots of maths. I haven't conducted extensive empirical testing to check how accurate it is, and accept no liability whatsoever for its predictions or your use of them. That said, the predicted results of the hanging poisitions on the show I made it for did turn out about right in practice.

Note that the calculator allows you to adjust the vertical pitch of the projector by altering the aim height but assumes that you will point the projector directly at the surface on the horizontal axis (i.e. no turning to the left or right).If you get an invalid result for the top or bottom width, it means the beam doesn't hit the cloth at that height.

New version! Now allows you to specify a beam angle, and the beam ratio gives more useful results.

Sample uses:

  • Planning how many projectors you need to fill a given width.
  • Finding out if a profile will cover the width of a flat at both the top and the bottom
  • Adjust the position values by trial and error to find an ideal rigging point for a projector or profile
  • If you have a fixed rigging point, and know how big an area you need to cover, alter the lens size or beam angle to find the most suitable option

VSFX Beam Size Calculator: javascript version

All dimensions are in metres apart from the lens size, which is in inches.

Projector height All heights are from the floor!

Cyc height How high is the top of the cyc?

Horizontal distance How far is the projector from the cyc bar?

Aim height The height at which the middle of the beam hits the cyc.

Lens size 2.5 3 4 5.5 6 8 10 I know my beam angle

Throw distance Distance from lens to aim point

Image Diameter How wide the image is at the aim height.

Image Radius

Top width How wide the image is at the top of the cyc.

Bottom width How wide the image is at the foot of the cyc.

Beam Ratio What proportion of the image is visible on the cyc.

diagram showing sizes referred to in calculator