When you buy a gobo image projector, one of the decisions you'll need to make is what kind of projection lens you want to come with it. This component is not to be confused with the gobo (the image carrier), rather, it is the equivalent of a camera lens and plays an important role in determining how far, wide, and bright your gobo image is projected.
A projection lens works like a camera lens, just in the opposite direction. It is used to guide and and focus the light that originates from the light bulb and travels through the gobo into a beam from your gobo projector. Without it, there would be no clear projected image.
Lenses are typically defined in focal length but for theatrical or promotional applications the beam angle is used instead. The beam angle already assumes a given gobo image size as specified by the gobo projector. Therefore it is often more practical to use the beam angle instead of focal length.
A narrower beam, typically between 5 and 15 degrees, is ideal for longer distances, such as when you're displaying an image on the outside of a building from hundreds of feet away. For most applications a lens angle between 15 and 25 degrees works well. A wider lens is used when you want the gobo to show up with a larger diameter at short distances. A good example is if the gobo is being used to light the wall behind a stage.
An important factor is the projection brightness. The smaller the image, the more light is concentrated and the brighter it projects. For example, if you double the image size by using a wider lens, you end up with only a quarter of the brightness. Therefore a smaller but brighter image may be preferred over a larger but darker image. This is especially true when you project darker colors, in bright environments or onto dark projection surfaces.
In any case, we highly recommend calling Gobosource.com to discuss your project to determine the ideal lens angle. This will ensure that you end up with a product you're happy with.
