Shutter Speed Calculator
Shutter Speed
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As Fraction
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Understanding the Exposure Triangle
The exposure triangle links shutter speed, aperture, and ISO. This calculator uses the APEX system: shutter speed t = N^2 / 2^EV, adjusted for ISO. EV (Exposure Value) represents scene brightness, with sunny days around EV 12-15 and dim indoors at EV 4-6.
Higher ISO values increase sensitivity, allowing faster shutter speeds. Doubling ISO is equivalent to one stop brighter. Wider apertures (smaller f-numbers) also admit more light.
Fast shutter speeds freeze action (1/1000s for sports), while slow speeds create motion blur. The reciprocal rule suggests using at least 1/focal-length for handheld shooting.
Frequently Asked Questions
What shutter speed freezes action?
Use 1/500s or faster for walking, 1/1000s for running or sports, 1/2000s or faster for birds in flight. For water, 1/500s freezes drops while 1/15s creates a smooth silky effect.
How does ISO affect shutter speed?
Doubling ISO lets you use a shutter speed twice as fast. Going from ISO 100 to 800 (3 stops) lets you go from 1/30s to 1/250s.
What EV values match common scenes?
EV 15: bright sun on sand/snow. EV 12-14: sunny to overcast. EV 8-10: bright indoors. EV 4-6: dim indoors.
What is the exposure triangle?
The exposure triangle describes the relationship between three camera settings that together determine how much light reaches the sensor: aperture (f-stop), shutter speed, and ISO. Changing one setting by one stop requires adjusting another by one stop to maintain the same exposure. For example, opening the aperture from f/8 to f/5.6 (one stop brighter) allows you to use a shutter speed one stop faster (e.g., from 1/125s to 1/250s) while keeping the same overall exposure.
What is the reciprocal rule for handheld shooting?
The reciprocal rule states that your minimum shutter speed for sharp handheld photos should be at least 1 divided by the effective focal length. For a 200mm lens, use at least 1/200s. For a 50mm lens, use at least 1/50s. On crop-sensor cameras, multiply the focal length by the crop factor first (1.5x for Nikon APS-C, 1.6x for Canon APS-C). Image stabilization in modern lenses and camera bodies can allow 2 to 5 stops slower than this rule suggests.
How do I photograph star trails or the night sky?
For sharp star points (no trailing), use the 500 rule: maximum shutter speed in seconds = 500 divided by the focal length. A 24mm lens allows roughly 20-second exposures before stars begin to trail. Use the widest aperture available (f/1.4 to f/2.8) and ISO 1600 to 6400. For intentional star trails, use exposures of 15 to 30 minutes or stack multiple shorter exposures in post-processing software.