Prism

What is and how to use a Triangular Prism in Photography

Recently I’ve had some interest in and questions about creative photography techniques so I thought these topics would be ideal for a few blog posts. 

Today, I’m going to talk a little about using a triangular prism as a creative tool in photography. A triangular prism is simply a five sided transparent glass object that is shaped, you guessed it, triangularly! It’s a readily available tool that is often used in grade school science to teach properties of light. In photography, this tool infuses beautiful creativity into a photograph. One of the fantastic things about this tool is that it is small and can easily be tucked into any camera bag. After some practice, it’s also very easy to use. This beautiful technique can infuse rainbows, light flare and reflections into an image. Here are a few tips that will help you be more successful when using a prism. 

1. Lens Choice

I think prisms work a little better with my telephoto lenses and I tend to use my prism most successfully with my 105mm. Perhaps it’s because of the small glass circumference on this lens in addition to this telephoto’s lighter weight. However, don’t be afraid to experiment with various lenses because prism use can work with all your lenses.

ISO 320, 105mm, 2.8f, 1/2000SS

ISO 320, 105mm, 2.8f, 1/2000SS

2. Aperture considerations

I recommend shooting in manual mode when using a prism or aperture priority mode as aperture is important when using a prism. I typically shoot with a wide aperture (3.2, 2.8, 2.2, 2.0) as this really does work well with the prism technique. The shallow depth of field from a wide aperture better blurs the prism itself and the artistic effect into the image.

ISO 400, 105mm, 2.8f, 1/400SS

ISO 400, 105mm, 2.8f, 1/400SS

3. Remove your lens hood

Prisms work best when they are close to your lens. It’s important to be careful when holding objects up near to the glass on your lens. You don’t want to accidentally scratch your lens. Most of the lenses I use with my prism are inlaid a bit from the lens casing but I’m still conscious of how I’m holding the prism in relation to my glass.

ISO 400, 105,, 3.2f, 1/1600SS

ISO 400, 105,, 3.2f, 1/1600SS

4. Focus

Focus is not always easy when you are holding an object up in front of your lens as your auto focus system will try and focus on the foreground object. When I’m shooting with a prism I play around a bit with the prism in front of my lens in order to get an idea about what position the prism will need to be in for the look I want. I then pull the prism away from the lens, focus on my subject, then quickly return the prism to it’s position and capture the image. This way my subject is in focus and my camera doesn’t try to focus on my prism. I use back button focus which I find works very well in this situation. BBF (back button focus) separates focus from the camera shutter. I’ve assigned a button on the back of my camera for focus. Separating focus and shutter allows me to not worry about my camera trying to focus prior to shutter release when I go to capture my image because I’ve already focused using BBF and focus and shutter release are not attained using the same button. Although much more tedious, but as an alternative to using BBF, you can focus on your subject then flip your camera into manual focus prior to releasing the shutter if focus and shutter are attached to the same button. The difficulty here is that we all know how fast children move. I find it much quicker to use BBF then quickly move the prism in front of my lens before depressing my shutter. The majority of my images are in focus using this technique.  

ISO 500, 200mm, 3.5f, 1/1250

ISO 500, 200mm, 3.5f, 1/1250

5. Light choice

Prisms work in all types of light but you will get different effects depending on the light available in the scene. So again, the idea here is to experiment. One note of caution is specific to very bright light. If you are backlighting your subject be careful when you are turning the prism as there is the potential to reflect the bright sun right through your lens and into your eye. If you have live view on your camera you can use this to prevent strong sun reflections into your eye via the viewfinder.  

ISO 200, 35mm, 2.5f, 1/200SS

ISO 200, 35mm, 2.5f, 1/200SS

6. Turn the prism

Here’s where the fun begins! Turning the prism is your key to creating your desired creative effect. The very basic science behind a prism is that when it is held up in front of a lens as light hits the prism it bends or refracts before it even enters the camera lens. The refraction of that light results in separation in the colours of light resulting in a rainbow being superimposed into your image. Prisms can also reflect light which often shows up as hazy flare into an image when it is held at a bit of an angle and further off to the side of the lens. Another gorgeous creative effect produced by a prism is reflection of the environment. This results in a double exposure look. This is best attained when the prism is held flat horizontally or vertical at the edges of the lens and tilted just a touch. Again, experimentation really is best! 

ISO 200, 105mm, 2.8f, 1/640SS

ISO 200, 105mm, 2.8f, 1/640SS

I adore creative photography and I never think there’s a right or wrong when it comes to infusing what you like into a creative image however one thing I do tend to keep in mind when using creative effects like a prism is that I want to use the technique in such a way as to not detract from my main subject rather I want to simply enhance the artistic quality of the capture. 

The most important thing to remember when shooting with a prism is to embrace the experimentation process! I think that’s part of the fun and uniqueness of prism use anyway!