Exposure Equivalents Calculator
Find equivalent camera settings that produce the same exposure value when you change aperture, shutter speed, or ISO. Useful any time you want to swap depth-of-field or motion blur without altering overall image brightness.
About this calculator
Exposure value is determined by three factors: aperture (f-number), shutter speed, and ISO. The amount of light reaching the sensor is proportional to ISO × shutterSpeed / aperture². To keep exposure constant while changing aperture, the new shutter speed must satisfy: targetShutter = (currentAperture² × currentShutter × currentISO) / targetAperture². This formula is derived by equating the exposure equations for both settings: currentAperture² × currentShutter × currentISO = targetAperture² × targetShutter × targetISO (assuming ISO is held constant). If you also change ISO, an additional scaling factor is applied. Mastering this relationship lets you freely trade depth-of-field against motion blur without re-metering the scene.
How to use
Suppose your current settings are f/2.8, 1/200 s shutter, ISO 400, and you want to switch to f/8 to gain more depth of field while keeping the same exposure. Step 1: Square both apertures: 2.8² = 7.84, 8² = 64. Step 2: Apply the formula: targetShutter = (7.84 × (1/200) × 400) / 64 = (7.84 × 0.005 × 400) / 64 = 15.68 / 64 ≈ 0.245 s. Step 3: Set your camera to approximately 1/4 s at f/8, ISO 400. The scene will be exposed identically to the original f/2.8 shot.
Frequently asked questions
How do I calculate equivalent exposure when changing both aperture and ISO at the same time?
When changing multiple exposure parameters simultaneously, you need to account for each change's effect on light. Start from the fundamental exposure equation: EV is constant when (ISO × shutterSpeed) / aperture² stays equal. Rearrange to solve for the one unknown you want to find. For example, to find the new shutter speed when both aperture and ISO change: newShutter = (oldAperture² × oldShutter × oldISO) / (newAperture² × newISO). This calculator assumes ISO is held constant, so if you change ISO, apply the ratio manually as an additional multiplier.
What is a stop in photography and how does it relate to equivalent exposure?
A stop is a doubling or halving of light. Opening the aperture by one stop (e.g., f/4 to f/2.8) doubles the light; closing it halves the light. Similarly, doubling the shutter speed or doubling the ISO each adds one stop of exposure. Equivalent exposures are combinations that differ by equal and opposite stops across parameters, so the total light remains the same. The formula captures this mathematically through the squared aperture ratio, reflecting that aperture area scales with the square of the f-number.
When would a photographer need to calculate equivalent exposure settings in the field?
A common scenario is switching lenses with different maximum apertures — for example, moving from a fast f/1.8 prime to an f/5.6 zoom. You need to know how much to adjust shutter speed or ISO to preserve the correct exposure. Another situation is intentional creative change: you want a longer shutter to blur water, which requires closing down the aperture to compensate. Sports photographers use equivalent exposure when the minimum shutter speed for freezing action forces them to recalculate ISO. Understanding equivalent exposures prevents over- or under-exposed shots during quick setting changes.