The concept of the camera obscura—a darkened space capturing an inverted image through a pinhole—has been understood for centuries. The real breakthrough came when someone asked: “How do we keep the image?”
The darkening quality of silver salts under sunlight led early experimenters to test various silver halide solutions. The great challenge wasn’t capturing the image, but fixing it—stopping the continued exposure to light so the picture wouldn’t vanish. This led to the three foundational chemical baths still used today in analog photography:
Developer – reveals the image,
Stop bath – halts the reaction,
Fixer (or “hypo”) – makes the image permanent.
Once this process was in place, the next hurdle was mastering exposure—what I like to call the dance. This dance involves three variables: ISO, shutter speed, and aperture.
Let’s begin with ISO, which defines the sensitivity of the film (or digital sensor) to light. A baseline of ISO 125 (formerly called ASA) is considered standard. Traditional films range from ISO 25 to 2000, with higher ISO being more sensitive but grainier. Early digital cameras also suffered from “noise” at high ISO, but modern sensors now handle ISO 32,000 with surprising clarity.
ISO 125 sets us up for the Sunny 16 Rule:
On a sunny day, with ISO 125 film, set your shutter speed to 1/125 sec and your aperture to f/16 for a perfect exposure.
From here, the dance begins. If your aperture opens wider (say, to f/1.2), more light enters—so you must compensate with a faster shutter speed to avoid overexposure. Each full stop change doubles or halves the light. The choices multiply, but the principle is simple: alter one, adjust the other.
For example:
f/1.2 at 1/1000 sec
f/8 at 1/125 sec
f/16 at 1/30 sec
All might yield the same exposure—but they do not create the same image.
The key difference is depth of field. A wide aperture like f/1.2 has a shallow depth of field—only a narrow slice of the scene will be in focus. Everything in front or behind becomes a pleasing blur. This is ideal for portraits or isolating subjects. But it demands precise focus, which is difficult in low light where you can’t see clearly.
On the other end, a small aperture like f/16 gives a deep depth of field. Almost everything will be in focus, which is why cheap disposable cameras with no focus controls rely on tiny apertures. They don’t need precision—just light and patience.
And that’s the dance: balancing time, light, and precision.
Photography is both science and intuition. It’s a partnership with light, where every image is the result of a decision made three ways. And once you begin to see it—not just the subject, but the shape and play of light itself—you’ll know when the rhythm is right.
