How to use
- Enter a reference ISO, aperture f-number and shutter time. Shutter time accepts seconds or a fraction such as 1/125; aperture accepts the number alone, such as 8.
- Choose the target setting to calculate: shutter time, aperture or ISO. Enter the other two target values. The selected field is read-only and ignored as an input.
- Set the desired nominal brightness change to zero for an equivalent combination. Positive stops request a brighter nominal result and negative stops a darker one. Alternatively choose Compare all settings and enter all three target settings; the change field is then ignored.
The initial values are editable examples, not detected camera settings. Enter plain numbers with a decimal point or decimal comma and without thousands separators. The range below each field states the supported limits. Press Calculate, or Enter in a field, to confirm the current inputs. The diagram above the fields updates immediately with valid settings, including the starting example. Editing clears the confirmed Result and Copy state; press Calculate to confirm again. Incomplete or invalid settings remove the preview geometry. Clear empties the numeric inputs, result and diagram; it keeps the calculation selection. Copy result copies the displayed values with labels. Calculations stay in your browser. Changing the site language opens a translated page and asks before leaving your current inputs; it does not convert a saved camera configuration.
Calculation and interpretation
This exposure calculator compares settings for the same scene and lighting. It can help exchange a longer shutter time for a smaller aperture, or estimate the ISO change needed to use a faster shutter. It does not inspect a photograph or measure the scene. Equivalent settings preserve a simple nominal brightness relationship, not motion blur, depth of field, noise or highlight capacity.
For ISO S, shutter time t in seconds and f-number N, nominal brightness is proportional to S × t / N². The stop difference from reference to target is log₂[(S₂t₂/N₂²) / (S₁t₁/N₁²)]. The three plotted contributions are log₂(S₂/S₁), log₂(t₂/t₁) and 2 × log₂(N₁/N₂). Their sum is the displayed change.
EV100 = log₂(100 × N² / (S × t)). This is a setting-derived value normalised to ISO 100. A target that is one stop nominally brighter has an EV100 one lower. EV100 is not the same as measured scene luminance, camera exposure compensation or the brightness of a processed JPEG. No light meter reading is taken here.
Worked examples
Reference ISO 100, f/8 and 1/125 s gives EV100 about 12.97. Keep ISO 100, choose target f/4 and solve shutter with zero change. The result is 1/500 s. Opening the aperture contributes +2 stops and shortening the exposure contributes −2, so the total is zero.
Keep the reference at ISO 100, f/8, 1/125 s. Set target f/8 and 1/500 s, choose ISO as the unknown and request zero change. The result is ISO 400. In Compare all settings, ISO 200 with the original aperture and time is +1 stop relative to the reference and has EV100 about 11.97.
Practical uses and limits
Use the comparison when planning motion rendering, tripod exposures or a change in aperture. The mathematically exact answer may fall between camera dial settings. Select the nearest available setting on the camera and compare that actual combination again to see the remaining difference. The calculator does not silently round to a one-third-stop dial sequence.
Inputs support ISO 1–1,000,000, f/0.5–f/128 and times from one microsecond to 86,400 seconds. Requested change is limited to −20 through +20 stops. If a solved value falls outside the same supported limits, the page shows an error instead of an unusable result or chart. These are calculation limits, not claims that a camera supports every value.
Lens transmission, filters, flash timing, reciprocity failure, ISO implementation and processing can alter real results. Increasing ISO does not increase the photons captured at a fixed aperture and shutter time. Use a test frame, histogram and suitable metering when actual exposure matters; this arithmetic does not guarantee a successful photograph or safe conditions for night photography.
Frequently asked questions
What does a positive stop difference mean?
The target has a higher nominal S × t / N² value. +1 doubles that value and −1 halves it. The EV100 difference has the opposite sign.
Why does changing f/8 to f/4 count as two stops?
Light admitted by the ideal aperture is proportional to 1/N². Halving the f-number multiplies that quantity by four, which is two doublings.
Can I compare settings without an unknown?
Yes. Select Compare all settings and fill both complete combinations. The tool calculates their actual stop difference; the requested-change field is ignored.
Will equivalent combinations look identical?
No. A faster shutter changes motion blur, aperture changes depth of field, and ISO can affect noise and headroom. The result preserves only the stated nominal relationship.