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Electronic Theatre Controls Inc

Changes in Light Angle from Source Four LED Series 2 to Series 3

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Introduction

The contents of this article are directly transposed from an ETC white paper released in 2022. The white paper can be downloaded at this link.

The release of Source Four LED Series 3 introduced new arrays that include a deep red LED, making them the most spectrally complete LED arrays available. The new Lustr X8 and Daylight HDR arrays provide beautiful, natural-looking light that can be infinitely tuned for any purpose. These new arrays utilized new LEDs that have different optical properties from those used in the past. Because of this change, there can be some differences in how the fixture operates (focuses), especially when using with templates or gobos. This document explains what has changed, what impact the change has, and provides some suggestions to help when working with the new fixture.

The Change

From the Series 2 to the Series 3 fixture, the cone angle of the light going through the gate increased. The main benefit of this change is that the amount of light that can go through the gate increases. This change was one part of the improvements that resulted in the higher light output of Series 3.

series_2_3_angle_change.png

The Effects

The positive effect of this change, as mentioned above, is that it allows more light through the gate and, ideally, through the projection lens. However, this change also has several other effects:

  1. The projection lens must grow in size in order to capture and transmit the increased angle of the light.
  2. The goal for a projection lens is to have the "plane" that represents the best focus across the field to be as flat as possible. In that way it can sit at the same plane as the gate and give a similar focus quality across the field. Increasing the light angle makes it more difficult to keep this plane flat.
  3. The depth of field for the projection lens decreases. As you adjust the focus on the projections lens, a given point on the image will stay in focus over a smaller range.
  4. Given (2) and (3), the focus process will get more challenging as the angle of the light through the gate gets larger.

Tips for Focusing

There are several things you can do to enhance the quality of the image and focus:

  • Use a donut in front of the lens. This improves the image quality by a certain amount, depending on the donut size (the smaller the donut, the larger the effect). Of course, keep in mind that this also reduces total brightness.
  • Use a smaller gobo. The focus quality tends to be best in the middle and get progressively more challenging as you  move to the edge of the gate. A smaller gobo keeps more of the image in the sweet spot of the lens.