The Aperture of Our Eyes


The same scene photographed with a large and small f-stop aperture, demonstrating the change in focus depth-of-field. Look closely at the window behind the plant and the reflection on the table. The focus was set on the lip of the pot and only the aperture was changed.

In my post, “The Shutter Speed of Our Eyes,” the shutter speed of a camera was compared to the human eye. Another feature of photography that can be compared to human vision is the aperture. In optics, an aperture is a hole that allows in light. As previously mentioned, the pupil and iris act like the aperture of a camera, regulating the amount of light that can travel through the lens into the retina. A better analogy would be that the pupil of the eye is “equivalent” to the diameter of a camera lens and the iris of the eye is “equivalent” to the aperture of a camera. In a dark environment, the pupils dilate (open) and in light, they constrict (close). If you look through a camera lens and dial the aperture setting, you will notice a similar dilation and constriction. On a camera lens, the numbers associated to aperture are defined as f-stops. This references the ratio of focal length to aperture diameter, creating a focal ratio or f-stop. A lower number defines a greater aperture opening, allowing in more light; a higher number, a smaller opening allowing less light to enter. Compared to a camera lens, the human pupil rests around 4 mm in diameter. In extreme dark, it dilates to approximately 8 mm (f/2.1). In bright light, it contracts to approximately 2 mm (f/8.3).

If you have experimented with depth-of-field in photography, you know that the higher the f-stop (smaller opening), the greater the depth-of-focus and the smaller the number (larger opening), the less depth-of-focus. When a photographer wants sharper focus from the foreground to the background, they use the maximum f-stop possible and focus on a near middle-ground object. Conversely, when just the subject is to be in focus, a minimum f-stop is selected, allowing everything in front and behind to fall out of focus. We experience a similar phenomenon in brightly lit scenes compared to dark environments. In extreme light, our eyes’ “aperture” becomes smaller, creating sharper focus and an expanded depth-of-focus. In darker scenarios, our eyes’ “aperture” becomes larger, creating softer focus and a contracted depth-of-focus.

As painters, understanding these tendencies allows us to better control our paintings’ depth. Since the main area of interest is the place where focus occurs, it should have the sharpest edges and contrast details, giving us the ability to manipulate the viewer into perceiving our intentions. Remember that the human experience isn’t the same as the camera’s. Since photography is heavily used as reference, it’s wise to understand its comparisons to human sight, to use it when needed, and to be a vigilant, sensitive observer of everything around us.


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