In photography, cinematography, and color grading, a “stop” (also called an “f-stop,” “exposure value” [EV], or “step”) represents a doubling or halving of the amount of light in an exposure. Increasing exposure by one stop means capturing twice as much light; decreasing by one stop means capturing half as much. This concept lies at the core of how image brightness, contrast, and dynamic range are measured and controlled. Understanding stops is fundamental for photographers, filmmakers, and colorists, as it directly affects the image's exposure, contrast, and dynamic range.

Human Vision and Contrast Ratios

A commonly cited figure for human vision is that we can perceive a total contrast ratio of around 1,000,000:1, corresponding to roughly 20 stops. However, this is the overall adaptive range—including the eye’s ability to adjust to dramatically different lighting over time (from near-total darkness to bright sunlight). In any single glance without time to adapt, the human eye often perceives closer to about 10–14 stops.

Despite this nuance, the human visual system still far exceeds the dynamic range of many displays. In comparison, standard dynamic range (SDR) monitors typically manage around 6 to 8 stops in typical viewing conditions—equating to a contrast ratio of 64:1 to 256:1 for most SDR content. This narrower range illustrates why SDR can struggle to reproduce the depth and detail that human vision can discern.

Dynamic Range and the Relation to Stops

Dynamic range, often expressed in stops, defines the contrast between the darkest and brightest parts of an image. Each additional stop represents a doubling of that dynamic range. For instance, a dynamic range of 14 stops corresponds to a 2^14:1 contrast ratio—or 16,384:1. Such a wide range allows modern cameras and HDR (High Dynamic Range) monitors to retain detail in both shadows and highlights, getting closer to the detail we see in real life.

How Does a Stop Affect Exposure?

A one-stop change in exposure always means doubling or halving the light captured. This principle applies equally to the three primary exposure controls:

1. Aperture (f-stop)

   • Going from f/2.8 to f/2.0 doubles the light (one stop more).
   • Going from f/2.8 to f/4.0 halves the light (one stop less).

   For those curious about why aperture values (f-stops) like f/2, f/2.8, f/4, and f/5.6 don't seem to double in a straightforward way, here's a simple explanation. These numbers relate to the size of the lens opening, which controls how much light enters the camera. Each step in the f-stop sequence actually represents a change in the area of the opening, doubling or halving the light. This is because the area of a circle (like the lens opening) is calculated using the formula (A = \pi r^2). To double or halve the light, the diameter of the opening must change by (\sqrt2) (approximately 1.414). Therefore, the values still effectively double, but account specifically for the circular shape of the aperture opening. So, while the numbers might look irregular, they are designed to ensure that each step doubles or halves the light entering the lens, taking into account the circular shape of the aperture. Hence the familiar sequence f/2.8 → f/4 → f/5.6, etc.)

2. Shutter Speed

   • Going from 1/60 s to 1/30 s doubles the exposure time (one stop more).
   • Going from 1/60 s to 1/125 s halves the exposure time (one stop less).

3. ISO Sensitivity

   • Going from ISO 200 to ISO 400 doubles sensitivity (one stop more).
   • Going from ISO 400 to ISO 200 halves sensitivity (one stop less).

Stops and Luminance

Because a stop is simply a factor-of-two change in light, it directly translates to measured brightness (luminance) in candelas per square meter (cd/m²), also known as “nits.” If a scene’s luminance is 100 cd/m², increasing by one stop raises it to 200 cd/m²; reducing by one stop lowers it to 50 cd/m².

HDR and SDR Monitors: Brightness Units Explained

Modern displays are often specified in "nits" (cd/m²). SDR monitors typically peak around 100–300 nits, while HDR monitors can reach 1,000–4,000 nits or more. From a stops perspective, raising brightness from 100 nits to about 1,600 nits is roughly a 4-stop increase (2^4 = 16×), meaning it is 16 times brighter.

SDR:

• Content is usually mastered for a peak of ~100 nits (in professional reference conditions), though many consumer SDR screens can produce a few hundred nits.
• In practice, SDR content often leverages about 6–8 stops (64:1 to 256:1 contrast) in typical viewing conditions—even if some LCD/OLED panels can measure higher contrast ratios in ideal lab conditions.

HDR:

• Designed for much higher peak luminance (1,000 nits or more) and very deep blacks, enabling a dynamic range of around 12–15 stops in many current displays.
• For instance, a 15-stop HDR monitor corresponds to a 2^15:1 = 32,768:1 contrast ratio—far closer to a camera’s or the eye’s capability in a single viewing.

HDR Monitors Bridging the Gap

High dynamic range (HDR) displays can often reproduce 12 to 15 stops or more, sometimes exceeding 30,000:1 contrast. This is a huge improvement over SDR and brings display capabilities closer to modern high-end digital cameras—helping preserve subtle shadow detail and bright highlights simultaneously. While still below the eye’s overall adaptive range of ~20 stops, HDR technology significantly narrows the gap, rendering images that are more vivid, detailed, and lifelike.

Summary

• A "stop" = The span of light doubled or halved.
• Dynamic range in stops translates directly to a 2^N:1 contrast ratio.
• Human vision can handle ~20 stops overall with adaptation, though ~10–14 stops instantaneously.
• SDR monitors typically encode ~6–8 stops, despite some panels having higher native contrast.
• HDR displays can show 12–15+ stops, with brightness often reaching thousands of nits (depending on the display technology).

Understanding stops and dynamic range is crucial for photographers, filmmakers, and colorists alike. It underpins exposure decisions and the final look of both SDR and HDR workflows, ensuring faithful reproduction of the subtle tonalities we see with our own eyes.