A Newtonian Escapade

The image is a representation of the ray diagrams for convex lenses many of us have studied in school physics. However, instead of being a single point, the focal point appears to be spread out as a line as a result of spherical aberration. Photograph/Rachit

The image is a representation of the ray diagrams for convex lenses that many of us have studied in school physics. Because of spherical aberrations, the focal point seems to be stretched into lines instead of a single point.  Photograph/Rachit Rawat

Rachit Rawat converts his physics experiment into his muse and photographs the refraction of light through a convex lens.

My Perspective

I got drawn into this concept after reading more about Newton’s Theory of Light. As an engineer, I was highly inspired to look at the movement of light closely and experiment with the movement. Moreover, I was thrilled to record this experiment by making images during the whole process. The result was truly mesmerising.

The Process

The actual process of shooting the image required me to operate the camera and then move the laser vertically along the center of the lens to generate the pattern seen in the image. All this had to be done in the absolute darkness. To get high contrast, everything not in the frame needed to be as dark as possible. I waited until it was night and then drew all the curtains shut. I placed black acoustic foam panels at various places around the setup where the laser beam was expected to hit to prevent it from reflecting off bright/smooth surfaces and lighting up the room.

The laser was set in a way that the beam was horizontal and out of the frame. The camera was set on manual mode with a 10 second timer. Once the focus was achieved, I switched off the light, pressed the shutter and fired the laser beam on the lens attached to the pipe.  To avoid high ISO and the noise that comes with it, I had to use smoke to reflect the laser beam and make its path brighter. To get the smoke, I took a couple of incense sticks, broke them into eight to ten segments of two inches each and stuck these in a single line in holes pierced into the top of a plastic container.

I used the adjustable center column of the tripod to lower the laser along the center of the convex lens while keeping the beam horizontal at all times. I moved it all the way down until the beam was out of the frame and then switched off the laser and waited for the exposure to complete. I had to experiment a few times to get the right exposure time. To get all the details in place, I photographed in RAW and enhanced the contrast and sharpness in post processing.


Diagram/Rachit Rawat

A word of caution here – embers from the burning incense sticks can burn through or set fire to inflammable substances. To keep the smoke from getting scattered I switched off the fan and shut the windows. I used a face mask and goggles to avoid irritation from the smoke and lit the incense sticks.

My Equipment

I looped a cable tie around the circumference of the lens and before pulling it tight, slipped another cable tie between the lens and the circumferential cable tie. Keeping the lens perpendicular to a PVC pipe, I tightened the second cable tie around the pipe. I suspended the pipe from a microphone stand and adjusted the microphone stand to get the lens at a comfortable height To achieve the desired composition and focus, I played around with the distance and zoom avoiding distortion. I set up the laser on another tripod to the left of lens in a way that the laser beam coincided with the principal axis of the convex lens. With this, the essential elements of this experiment were in place.

Camera: Sony Alpha NEX-5T

Lens: Sony E 18–200mm f/3.5-6.3 OSS (SEL 18200)

Aperture: f/4.5

Shutterspeed: 30secs

ISO: 200

Focal length: 39mm

To see more of Rachit’s photography, you can visit his Instagram account @seensomewhere

Tags: assignment, better photography, convex lens, engineering, experimentation, Mumbai, photography, physics, rachit, refraction