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Learn How We Can Keystone-Correct Your Gobos

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https://www.rosco.com/spectrum/index.php/2016/06/keystone-correct-your-gobos/
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We’ve all been there – you have an area that you want to project a gobo onto (usually a blank wall), but the only point you’ve got to place a fixture is nowhere near a straight shot, and the gobo you want to project ends up getting warped out of shape. That’s called keystoning – and, with a little information ahead of time, we can fix that for you!

Keystoning2bTo illustrate this issue, we’re using one of our most popular gobo combinations: R77802 Stained Glass Window Composite and R43801 Kaleidoscope Prismatic inside a Universal Iris Slot Gobo Holder. This is a popular combination because it provides easy stained glass window imagery that creates an instant church setting on stage for productions like The Sound of Music, Romeo & Juliet and Footloose. Each of those shows have brief scenes that take place inside a house of worship, a setting that can be quickly created by projecting a stained glass window or two on the wall.

What if, however, the only spot you’ve got to project from is too angled and causes keystoning like in the image above? We can keystone correct that gobo – but we need some information from you when you order the gobo. You can supply us that information two ways – the Geometry Way or the Visual Way.

The Geometry Way

Don’t Panic! We are not going to ask you to do geometry. We’ll do all of the calculations for you – specifically, if you’ll recall from Geometry 1, we’ll be executing the Pythagorean Theorem!

We can calculate the amount of keystone correction needed for your gobo if you supply us with the dimensions of your projection setup. Here’s what we need to know:

  • The spread of your throw in degrees (19°? 50°?)
  • The distance of your fixture to the projected surface
  • The height of the beam – measuring the center of the beam


Basically, we’re making a triangle, and we need to know the lengths of at least two of the edges. As an example, let’s say that you’ve got a 26° Source 4 that is only 8’ from the back wall you’re projecting onto, and you want the center of that beam to be 20’ down from the electric. Using the Pythagorean Theorem, we can determine that your throw distance is 21’ 6” and then we can calculate the necessary keystone correction for your gobo.

 The Visual Way

The first thing you need is a Lineup Grid gobo. It’s a gobo you probably don’t have – but you should. Contact your local Rosco dealer today and order R77888 Lineup Grid. Hang the fixture exactly where you need it, choose the proper barrel/lens and aim this gobo exactly onto the surface you’ll be projecting onto. Then, take a picture of the results.

Keystoning7

Your image of the projected Lineup Grid gobo will help us determine how much keystone correction is needed. When it’s time to order the gobo you need, simply email the picture you took of the projected Line Up Grid gobo to your Rosco dealer and have them reference that keystone correction image when they order it for you. Due to the fact that we’ll have to re-tool our machinery, the gobo would be a custom gobo, which means that custom gobo pricing and lead-times will apply – time and money well-spent for a good projected image.

Keystoning8With a little help from our world-class gobo manufacturing team, the gobos have been keystone-corrected to project realistic stained glass windows on stage. Using this technique, you can take the audience to church in any production with a house of worship setting.

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Joel Svendsen

About Joel Svendsen

Content Marketing Manager: Joel's Rosco career began in Rosco's Hollywood office in 1999 – first in sales covering the Western US and the Los Angeles Film & Television market, and then as Product Manager for Rosco's Film & Television Products. In that time, his knowledge of Rosco's products and how they're used in each of our marketplaces makes him well suited for bringing the stories in Spectrum to life.