Understanding the Freeform Lens Parameters

Maximum Threshold

The Maximum Threshold is available when you create a Freeform Lens based on an Intensity Target Type with an Intensity File.

The Freeform Lens works only in refraction. However, according to the intensity distribution of the file which can display light on a half-sphere, raking rays on edges are not refracted and the Backface of the Freeform Lens cannot be designed correctly. Thus the Maximum Threshold has been introduced to overcome this issue.

The goal of the Maximum Threshold is to define a threshold above which rays will be considered in the construction of the Backface, and under which rays will not be considered, therefore removing these potential raking rays that prevent a correct design.

Maximum Threshold can be set between 1 and 100 and is considered along the optical axis.

In the schematic example below, the Maximum Threshold is set to 65 of the intensity distribution peak. This creates a 43 angle. Then, only rays included in the solid angle created by the Maximum Threshold will be used to design the back face (green part). Rays outside the solid angle (red part) will not be used, such as raking rays.

Resolution Factor

The Backface is designed according to the Inverse Simulation principle. Rays are launched from the Target input, then the Backface is designed according to the result expected. However the Freeform Lens computation may sometimes lack rays to correctly design the Backface. Thus, the Resolution Factor parameter has been introduced to overcome the lack of rays.

The goal of the Resolution Factor is to densify the number of rays launched from the target (intensity file or image) to allow Speos to better design the Backface of the Freeform Lens.

The Resolution Factor is a multiplier of the resolution of the target.

Intensity File (Intensity Target)

In case of an Intensity File, the resolution is set to 180 on Theta and 180 on Phi.

According to the Maximum Threshold defined, only the rays included in the solid angle are considered to design the Backface. But this rays number may not be high enough to design correctly. Thus, the Resolution Factor multiplies the resolution of the Intensity File so that more rays are included in the solid angle to design the Backface.

In the schematic example (figure 1), the number of rays included in the solid angle is not enough.

In the schematic example (figure 2), a Resolution Factor = 2 has been applied to get a Intensity File resolution = 360. By extension, the number of rays included in the solid angle has doubled on Theta and doubled on Phi.

Figure 1. Resolution Factor = 1

Figure 2. Resolution Factor = 2

Figure 3. Real Example of Resolution Factor Impact on Intensity Target

Image (Irradiance Target)

In case of an Image, the resolution corresponds to the resolution of the image. For each pixel of the image, one ray is emitted. However the number of rays may not be enough sometimes.

The Resolution Factor multiplies the number of rays emitted per pixel on the vertical resolution and the horizontal resolution of the image.

In the schematic example (figure 4), the resolution of the image is 4 * 4, meaning 16 pixels. With a Resolution Factor = 1, one ray per pixel is emitted, resulting in 16 rays emitted.

In the schematic example (figure 5), the resolution of the image is 4 * 4, meaning 16 pixels. With a Resolution Factor = 2, four rays per pixel are emitted, resulting in 64 rays emitted.

Figure 4. Resolution Factor = 1

Figure 5. Resolution Factor = 2

Figure 6. Real Example of Resolution Factor Impact on Image Target