Saturday, May 13, 2017

Throwing Light #3 - Masks and Gobos

Part 1 - Part 2 - Part 3

Now that I know some basic ways to "throw" light, I wanted to explore how to shape the rays into specific patterns. To find out, I printed a quick (and sloppy) series of masks to test how they affected the shape and quality of light.

Like the previous experiments, I used the Circuit Playground board from Adafruit. I used the larger, deeper version of the 3D printed medallion I created in Part 2. The masks fit over the front of the openings in the light channels. I did not realize how much light would leak out from around the masks (as you can see in the photos) but the masks are enough to test some basic techniques.

The version of the medallion with a reflective interior (at right in the photo above) was not affected by the masks; it's almost useless. But the masks do have a pronounced affect on the raw black PLA version at the left.

The 3D printed set of masks (in red) sits under Circuit Playground board. The Medallion slips over the top of this assembly.
Surprises and Successes

I have played with masks and gobos for photography and stage lighting, so I sort of knew what to expect from the different shape. But the sizes and distances are so much smaller here that I expected some slight differences.

Most of the masks gave the expected results, but there were a few surprises:

The biggest surprise came with the "posts" mask. I printed one set of 1x1mm posts and a second set that was also 1mm wide but 4mm deep. I expected the deeper posts to cast the stronger shadow like it does in a large scale mask. Instead, the skinny 1x1 posts yielded the more precise shadows. I think this might be because of the small scale. The sides of the larger posts may reflect so much light that the shadow gets diffused from all the scattered light.

I was also hoping that the masks might be strong enough to shape the light from the reflectively painted version of the medallion. Unfortunately, the scattering overpowered the masks and there was negligible shaping from the masks.

SURPRISE!!! The skinny 1x1 posts actually created a stronger shadow that the deeper posts. I think the sides of the deep posts reflect and scatter too much light and negate the mask's shadow making. This is true even with the reflective version.

Bigger is better - sometimes. I wanted to see if a pinhole was large enough to create a visible ray -it was NOT!!! However, the larger round hole did emit a slightly shaped ray.

The vertical slot worked as expected, The diagonal slot worked sort of like I expected (a slight gradient) but it is the only shape that actually worked better with the reflective interior (see comparison photo above)

Aha, these worked exactly as expected. The "high slot" caused the beam to appear at a distance from the opening of the light channel.