prism

How to create the world's best optical prism.

Designing a new class of optics is tough. How does one approach it?

The quest to improve today's tools continues.


GIVEN THAT some arts evolve quicker than others, prism photography has been especially slow to become adopted by photographers at large. 'Prisming' has gained some traction in recent years through the blogs of heavyweight photographers—but the art has yet to reach a mainstream audience. Why is that? It is certainly capable of complementing a photographer's image with attractive abstractions:

Violet Short Photography

And prisming just makes sense. Busy photographers are trying to do less post-production work and achieve better results in camera. Prism photography seems to give us the best of both worlds: pleasing optical effects that can be achieved easily without having to bend over backwards. It's definitely easier than steel wool photography or even Von Wong's underwater shoot above a layer of toxic hydrogen sulfide. Still, the art has been slow to catch on.

The equilateral prisms that most people use are not good tools for prism photography. They're obviously not designed for photography (being that they're at least a few hundred years older than photography itself), yet they remain a cheap and readily available tool.

photographer-wtih-prism

Photographer using a prism.

If we could design a better tool, we could create better art, and the prisming could spread faster. The question becomes: how can we build a better prism, than the equilateral prism itself?

Let's try to see what photographers are currently using, and what the downsides of that approach are:

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The photographer's default prism tool: the equilateral prism

Let's pretend the yellow lines represent rays of light that are traveling into the camera, and the white triangle is a cross-sectional view of an equilaterial prism that is sitting in front of a photographer's lens. The equilaterial prism will reflect light dependent on how it's normals sit relative to the lens as per a few interesting light principles. Let's pretend that we're using our prism to try to augment a shot of a palm tree—how will the prism impact our photography?

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Top: Example prism position; Bottom: Example output image

Well this didn't quite work. Holding the prism with one face parallel to the lens reflects light in such a way that we cannot even see what is directly in front of the lens! Unfortunately, the prism is refracting light from the surrounding ground and the sky into the shot. If we want to get the palm tree into our frame, we can do one of two things:

  • Rotate the prism until light refracting from the palm tree enters the lens
  • Move the prism slightly out of the field of view so that we can shoot past it, allowing the lens to get direct line of sight with the palm tree

Prisms can throw light in unpredictable directions, so we know from experience that rotating it clock or counter-clockwise may or may not give us the results we want. Instead, let's try moving the prism down, so the top half of our field of view is exposed and the bottom half is covered by the prism:

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Top: Example prism position; Bottom: Example output. Yuck! There is too much going on here.

We can now see our palm tree, but this shot leaves a lot to be desired. It's ugly. It's simply not a good picture. Why would we want to use a prism here? We probably would have had a better shot not using the prism at all!

This is the current problem with prism photography. Equaliteral prisms throw all the reflected abstractions to one side of the frame, which usually looks compositionally strange (like in this shot, above). This is exactly the result people are getting using equilateral prisms today. And it's so hard to get a good effect that people are not picking up prism photography at all. Not surprising. Again, equilaterial prisms are not designed for photography—and it's hard/impossible to craft great compositions with them.

So, how can we create something better? Let's focus on making something that can be used to achieve interesting compositions. Understanding that pushing all of the prism's reflected abstraction to the side of the image looks strange—let's try to design a piece that can create more flexible compositions.

We want to make a prism that allows us to create compositions that are focused on our subject whilst still creating cool prism abstractions. Creating a prism that doesn't obstruct our subject is easy. If we just used a flat piece of glass, the light will shine straight through, as if the glass wasn't even there:

prism-light-shine

Flat glass in front of the lens

Obviously, this doesn't allow us to do any prisming! What we could do though, is make the piece of glass thicker, and add facets on the sides of the glass that do allow us to prism.

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Top: Example prism position; Bottom: Example output. This is starting to get a lot better!

This is quickly becoming a lot more desirable. We notice that the prisming effect is happening around the edges of the image—ever so slightly at the top left and heavily at the bottom right. Even cooler, changing the angular position of the prism to the lens allows us to do exactly what we want—add more prisming on the bottom, left side, right side, top, or—really, wherever. We now have total control. A few more examples:

prism-light-shine

The prism effect wraps the subject on the bottom and right halves of the frame.

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The prism effect wraps the subject completely.

This was the thought process that was in play when creating the new Julia Penrose & Pascal filters. We've been pretty happy with the effects that these new prisms have been able to achieve.

What do you think?

Published by Nikk Wong

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