Exposure Calculator — ISO, Aperture & Shutter Speed
Exposure Value (EV)
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Lighting Condition
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Equivalent Setting
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How Exposure Value (EV) Works in Photography
Exposure value (EV) is a standardized number that represents a specific combination of camera settings -- aperture, shutter speed, and ISO -- that produce the same overall image brightness. The concept was formalized in the 1950s by the German shutter manufacturer Friedrich Deckel and adopted as an industry standard. According to the International Organization for Standardization (ISO 2720), EV 0 is defined as a 1-second exposure at f/1.0 and ISO 100. Each increment of +1 EV halves the light reaching the sensor, while -1 EV doubles it.
The exposure triangle consists of three interdependent settings: ISO (sensor sensitivity), aperture (lens opening size measured in f-stops), and shutter speed (exposure duration). This calculator computes the EV from your current settings, identifies the lighting condition, and provides an equivalent exposure alternative. Understanding these relationships lets you make creative trade-offs -- for example, shifting from f/8 at 1/250s to f/2.8 at 1/2000s for shallow depth of field while maintaining identical brightness. Our focal length equivalent calculator complements this tool for crop-sensor conversions.
The Exposure Value Formula
The standard EV formula at ISO 100 is:
EV = log2(f^2 x ShutterSpeed / ISO)
Where f is the aperture f-number and ShutterSpeed is the reciprocal of the exposure time in seconds (e.g., 1/125s = 125). Each variable is defined as follows: f-number = focal length / diameter of the lens aperture (e.g., f/5.6); Shutter speed = the denominator of the exposure fraction (e.g., 125 for 1/125s); ISO = sensor sensitivity (base 100).
Worked example: At ISO 100, f/5.6, 1/125s: EV = log2(5.6^2 x 125 / 100) = log2(31.36 x 1.25) = log2(39.2) = 5.29. This corresponds to a moderately dim interior. Changing to ISO 400 while keeping the same aperture and shutter speed: EV = log2(31.36 x 125 / 400) = log2(9.8) = 3.29, meaning the camera is capturing 4 times more light (2 stops brighter).
Key Photography Terms Explained
- Stop: A doubling or halving of light. Moving from ISO 200 to ISO 400 is one stop brighter. Moving from f/4 to f/5.6 is one stop darker.
- Aperture (f-stop): The size of the lens opening. Lower numbers (f/1.4, f/2) mean larger openings and more light. The f-number sequence follows a sqrt(2) progression: f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22.
- Reciprocity: The principle that equivalent exposures can be achieved through different combinations of aperture, shutter speed, and ISO, as long as the total light captured remains the same.
- Dynamic Range: The range of EV values a camera sensor can capture in a single frame. Modern sensors achieve 12-15 stops of dynamic range, meaning they can record detail from very dark shadows to bright highlights simultaneously.
- Depth of Field (DoF): The zone of acceptable sharpness in an image. Wider apertures (lower f-numbers) produce shallower DoF, which is why portrait photographers favor f/1.4-f/2.8 for background blur (bokeh).
EV Values for Common Lighting Conditions
The table below maps EV values to real-world lighting scenarios, helping photographers estimate camera settings before metering. These values are referenced at ISO 100 and are based on the ANSI standard exposure tables.
| EV (ISO 100) | Lighting Condition | Example Settings |
|---|---|---|
| -4 to -2 | Starlight, Milky Way | f/2.8, 20s, ISO 3200 |
| -1 to 2 | Full moon, dim streets | f/2.8, 4s, ISO 1600 |
| 3 to 5 | Dim interior, candlelight | f/2.8, 1/15s, ISO 800 |
| 6 to 8 | Indoor lighting, office | f/4, 1/60s, ISO 400 |
| 9 to 11 | Overcast sky, open shade | f/5.6, 1/125s, ISO 200 |
| 12 to 14 | Sunny day | f/11, 1/125s, ISO 100 |
| 15 to 16 | Bright snow, beach, desert | f/16, 1/250s, ISO 100 |
Practical Exposure Examples
Example 1 -- Portrait with background blur: Starting at f/8, 1/125s, ISO 100 (EV 13, sunny day). To achieve shallow depth of field, open to f/2.8 (3 stops brighter). Compensate by increasing shutter speed 3 stops: 1/125 to 1/1000s. New settings: f/2.8, 1/1000s, ISO 100. Same brightness, dramatically different look. Use our image resolution calculator to check if your final image resolves enough detail.
Example 2 -- Freezing sports action in dim light: Stadium lighting at EV 7. You need at least 1/500s to freeze motion. At f/2.8, 1/500s: required ISO = f^2 x ShutterSpeed / 2^EV = 7.84 x 500 / 128 = 30.6, round to ISO 3200 for practical purposes. Modern cameras handle ISO 3200 with manageable noise.
Example 3 -- Long-exposure waterfall: Bright daylight at EV 14. You want a 2-second exposure for silky water. At ISO 100, 2 seconds (1/0.5): required f-stop = sqrt(2^EV x ISO / ShutterSpeed) = sqrt(16384 x 100 / 0.5) = impossibly large. Solution: add a 10-stop neutral density filter, effectively reducing the scene to EV 4, allowing f/8 at 2 seconds at ISO 100.
Tips for Better Exposure Control
- Learn the Sunny 16 Rule: On a sunny day, correct exposure is f/16 at a shutter speed equal to 1/ISO. At ISO 100, that means f/16 at 1/100s. This rule provides a reliable starting point without a light meter.
- Expose to the right (ETTR): When shooting RAW, slightly overexpose (without clipping highlights) to maximize shadow detail. RAW files contain more tonal information in bright areas than dark areas.
- Use the histogram: The histogram is more reliable than the LCD screen for judging exposure. A well-exposed image has data spread across the full range without clipping at either end.
- Bracket for HDR: Shoot three exposures at -2 EV, 0 EV, and +2 EV, then merge in post-processing for scenes with extreme dynamic range (e.g., interior looking out a bright window).
- Know your camera's ISO ceiling: Every camera has an ISO above which image quality degrades noticeably. For most APS-C sensors this is around ISO 3200-6400; for full-frame sensors, ISO 6400-12800. Plan your flash guide number settings if you need more light without raising ISO.
Frequently Asked Questions
What is exposure value (EV)?
Exposure value is a standardized number representing the brightness level of a scene or the combination of camera settings (aperture, shutter speed, ISO) that produce a specific image brightness. EV 0 is defined as a 1-second exposure at f/1.0 at ISO 100, per the ISO 2720 standard. Each +1 EV increment halves the light (one stop darker), while -1 EV doubles it. Typical outdoor daylight ranges from EV 12 to 16, indoor lighting from EV 5 to 8, and night photography from EV -4 to 2. Understanding EV helps photographers quickly translate between lighting conditions and camera settings.
How do ISO, aperture, and shutter speed relate?
These three settings form the exposure triangle, where each controls one aspect of light capture. Doubling ISO (e.g., 100 to 200) doubles sensor sensitivity -- one stop brighter. Opening aperture by one stop (e.g., f/8 to f/5.6) doubles the light entering the lens. Halving shutter speed (e.g., 1/500s to 1/250s) doubles the exposure time. Changing one setting by one stop requires compensating with another to maintain the same exposure. For example, ISO 100, f/8, 1/250s is equivalent to ISO 400, f/8, 1/1000s -- both produce identical brightness despite very different settings.
What EV values correspond to common lighting conditions?
At ISO 100: EV -4 to -2 corresponds to starlight and the Milky Way. EV -1 to 2 covers full moonlight and dimly lit streets. EV 3-5 represents dim interiors and candlelight. EV 6-8 is typical indoor lighting (offices, living rooms). EV 9-11 covers overcast skies and open shade. EV 12-14 is direct sunlight. EV 15-16 represents extremely bright conditions like sunlit snow or sandy beaches. These values are referenced in the ANSI standard exposure tables and serve as the foundation for light meter calibration.
What is the Sunny 16 Rule?
The Sunny 16 Rule is a time-tested exposure guideline stating that on a bright, sunny day, correct exposure is achieved at f/16 with a shutter speed equal to the reciprocal of the ISO setting. At ISO 100, that means f/16 at 1/100 second. At ISO 200, f/16 at 1/200 second. Variations include: f/11 for slightly overcast conditions, f/8 for overcast skies, and f/5.6 for heavy overcast or open shade. This rule was widely used before in-camera light meters became standard and remains useful as a quick sanity check for your meter readings.
How do I calculate the correct shutter speed to avoid camera shake?
The classic reciprocal rule states that your minimum shutter speed should be 1/(focal length in mm) when shooting handheld. For a 50mm lens, use at least 1/50 second; for a 200mm telephoto, at least 1/200 second. On crop-sensor cameras, multiply the focal length by the crop factor first (e.g., 50mm on a 1.5x crop = 75mm equivalent, so use at least 1/75s). Modern image stabilization (IS/VR/OIS) provides 3-5 stops of compensation, allowing the use of 1/15s with a stabilized 50mm lens. For sharp results in critical work, use a shutter speed twice the reciprocal rule minimum.
What is the difference between one stop and one-third of a stop?
One full stop doubles or halves the light. Most modern cameras allow adjustments in one-third stop increments for finer exposure control. The aperture sequence in third-stops between f/4 and f/5.6 is: f/4, f/4.5, f/5.0, f/5.6. The ISO sequence in third-stops between 100 and 200 is: 100, 125, 160, 200. The shutter speed sequence between 1/125s and 1/250s is: 1/125, 1/160, 1/200, 1/250. Third-stop adjustments are particularly useful when fine-tuning exposure to avoid highlight clipping or shadow loss in high-contrast scenes.