Exposure Equivalent Calculator

How Exposure Equivalent Calculator Works

Aperture, shutter speed, and ISO all control exposure along the same scale of "stops," and any one of them can be traded for either of the other two while keeping the photo equally bright. This calculator does that trade for you: change one setting for its own creative reason (a wider aperture for background blur, a faster shutter to freeze motion, a lower ISO for less noise) and see exactly what the other two would need to become to compensate.

Formula & Method

A "stop" is a doubling or halving of light. Aperture stops are 2 × log₂(N_old / N_new) since f-number is a ratio and light scales with its square (going from f/8 to f/5.6 is one stop). Shutter stops are log₂(t_new / t_old), and ISO stops are log₂(ISO_new / ISO_old), since both scale linearly with light. Once the stop change from your edited setting is known, the calculator applies the exact opposite stop change to each of the other two settings independently, showing what either one alone would need to become to hold total exposure constant.

Worked Example

Starting at f/8, 1/250s, ISO 400, opening the aperture to f/4 lets in 2 more stops of light. To keep the same exposure, either the shutter speed needs to go 2 stops faster (1/250 → 1/1000) while ISO stays at 400, or the ISO needs to drop 2 stops (400 → 100) while the shutter stays at 1/250 -- both produce an identical overall exposure to the original settings.

Frequently Asked Questions

Why does the calculator show two different "new" values instead of just one?

Because compensating for a change in one setting is a choice, not a single answer -- you could adjust shutter speed, ISO, or some mix of both to offset an aperture change, and which one makes sense depends on your priority (avoiding motion blur vs. avoiding noise). The tool shows both single-setting options so you can pick whichever trade fits the shot.

Why does the hint mention that "f/11" and "1/125s" aren't their exact values?

The marked stops on a real camera are rounded for legibility -- the standard full-stop sequence (f/1.4, f/2, f/2.8...) is really based on multiplying by √2 each time, so "f/11" is actually about f/11.3, and shutter speeds like "1/125" are actually about 1/128s (a power of 2). This calculator uses the exact mathematical stop values, so its output may need rounding to your camera's nearest marked setting.

Can I enter a shutter speed as a whole number of seconds?

Yes -- the shutter speed fields accept either a fraction like 1/125 for fast speeds or a plain number like 2 for a 2-second long exposure; the calculator detects which format you've entered automatically.

What does a positive vs. negative "stops changed" mean?

A positive number means your edited setting now lets in more light than before (e.g., a wider aperture or slower shutter), and a negative number means it lets in less -- the compensating adjustments to the other two settings always move in the opposite direction, since they need to remove or add back exactly the light your change altered.