Or: What’s the ISO of a human eye?
I have worn glasses all my life, and as a result, I was introduced to the magic of optics way before I ever considered getting into photography.
Then, when I started learning more about the magic of photography, I started noticing things with my own eye-sight: For example, in bright daylight, I can see further than in twilight. Why? I’ll leave you to solve this one yourself (think about it!) — the solution is at the end of this article.
As a photographer, I’m often intrigued by the physics of how photography is similar (and different) to how my eyes work — so I figured it was time to write a little article about how it all hangs together.
To better understand the answer to this question, let’s first have a quick comparison of various similarities and differences found in the working of the human eye and a photo camera.
Image focusing: Human and camera lenses both focus an inverted image onto light-sensitive surface. In the case of a camera, it’s focused onto film or a sensor chip. In your eyes, the light-sensitive surface is the retina on the inside of your eyeball.
Light adjustment: Both the eye and a camera can adjust quantity of light entering. On a camera, it’s done with the aperture control built into your lens, whilst in your eye, it’s done by having a larger or smaller iris.
Absolute versus subjective measuring of light: Simply speaking, the human eye is a subjective device. This means that your eyes work in harmony with your brain to create the images you perceive: Your eyes are adjusting the focus (by bending the light through the lens in your eyeballs) and translating photons (light) into an electrical impulse your brain can process. From there onwards, it’s all about your brain: It is continuously readjusting its colour balance according to the lighting context. In other words, our eyes know what must…
As an enthusiast deeply immersed in the realms of both optics and photography, my extensive background in these subjects allows me to shed light on the intriguing interplay between the human eye and a camera. Having explored the intricacies of optics since my early days, which were influenced by a lifetime of wearing glasses, I discovered the wonders of vision long before delving into the captivating world of photography.
The exploration of photography's magic led me to notice peculiarities in my own eyesight, such as the ability to see further in bright daylight compared to twilight. This observation naturally sparked a curiosity that impelled me to understand the underlying physics connecting the functioning of the human eye to that of a camera.
To address the question posed in the article—"What’s the ISO of a human eye?"—we must first delve into the foundational similarities and differences between the human eye and a camera. Both systems share the fundamental principle of image focusing, where lenses play a crucial role in projecting an inverted image onto a light-sensitive surface. In the case of a camera, this surface is film or a sensor chip, while in the human eye, it is the retina located on the inner surface of the eyeball.
Another parallel between the two lies in their ability to adjust the quantity of light entering the system. Cameras achieve this through an aperture control integrated into the lens, while the human eye accomplishes it by altering the size of the iris.
One key distinction arises in the realm of light measurement. The human eye operates subjectively, working in tandem with the brain to create the images we perceive. This process involves continuous adjustments to focus and the translation of light into electrical impulses for the brain to process. Unlike a camera, the human eye is not an absolute measuring device; instead, it adapts dynamically to different lighting conditions, continuously readjusting color balance to suit the context.
To solve the riddle posed in the article—why one can see further in bright daylight compared to twilight—one must consider the dynamic interplay of the eye's focus adjustment and the brain's continuous recalibration in response to changing lighting scenarios. In essence, the human eye's adaptive nature allows it to optimize vision in various conditions, showcasing the intricate harmony between biology and optics.
