Free calculator
Exposure Calculator
One stop more light at T2.8, 180° and ISO 800 is cut by closing to T4, a 90° shutter, ISO 400 or an ND 0.3: pick one. Enter your settings and any change in stops, thirds included, to see what each control has to do on its own.
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This web tool writes values of 10,000 and up in full (ISO 12,800) and keeps each field to a realistic range. Save, share and get the Pro tools in the app.
How it works
T′ = T × √2^EV angle′ = angle × 2^(−EV) ISO′ = ISO × 2^(−EV) ND density = |EV| × 0.3A stop is a doubling or halving of light. A positive EV change means more light reached the sensor (the sun came out, a lamp went up) and has to be cut; a negative one means light was lost and has to be put back. Each formula gives the full compensation by one control, so the four answers are alternatives: change one of them, not all four.
Where
- T
- the T-stop you are on now
- angle
- shutter angle(°)
- ISO
- ISO or exposure index
- EV
- the change in stops, + for more light; fractions such as −1/3 work
nearest of T1, 1.1, 1.3, 1.4, 1.6, 1.8, 2, 2.2, 2.5, 2.8, 3.2 … 22, 25, 29, 32 by |log₂(T′ ÷ marking)|The exact T-stop is rounded to the nearest third-stop marking, measured in stops rather than in numbers. When the exact value is 0.05 stop or more from the marking, both are shown: +1.5 stops from T2.8 is "T4.5 (exact T4.71)".
density = stops × 0.3; light through = 1 ÷ 2^stopsEach 0.3 of density is one stop: ND 0.3 is one stop (ND2, half the light), ND 0.9 three stops (ND8, an eighth). A change within 0.15 stop of a whole stop from 1 to 10 shows that filter; anything else shows the exact density and the nearest whole-stop filter, such as "ND 0.45 (nearest ND 0.6 · ND4)" for 1.5 stops.
Thirds of a stop
Type a change as a fraction, with the sign in front: +1/3, −2/3 or +4/3. One-third of a stop more light at T2.8 is T3.2 (exact T3.14), a 142.9° shutter, ISO 635, or an ND 0.10. Decimals work too: 1.5 is a stop and a half. Mixed numbers such as 1 1/3 are not read; type 4/3 instead.
The warnings
The calculator flags an answer you probably can't use: a shutter angle outside 1–358°, an ISO outside 50–25,600, or a T-stop beyond T1–T32. It also notes when the shutter moves far from 180° (under 90° looks crisper and more staccato; over 270° blurs motion more), and that removing ND only works if a filter is in.
Worked example
Two-thirds of a stop less light at T2.8, 180°, ISO 800
- T-stop: 2.8 × √2^(−2/3) = 2.22 → T2.2
- Shutter: 180° × 2^(2/3) = 285.7°
- ISO: 800 × 2^(2/3) = 1270
- ND: |−2/3| × 0.3 = 0.20 density; the nearest whole-stop filter is ND 0.3
Open to T2.2, or go to 285.7°, or ISO 1270, or remove ND 0.20 (nearest ND 0.3 · ND2): one of them
Quick reference
Compensating a change at T2.8, 180°, ISO 800 (each column on its own)
| EV change | T-stop | Shutter angle | ISO | ND filter |
|---|---|---|---|---|
| +3 | T8 | 22.5° | 100 | Add ND 0.9 (ND8) |
| +2 | T5.6 | 45° | 200 | Add ND 0.6 (ND4) |
| +1 | T4 | 90° | 400 | Add ND 0.3 (ND2) |
| +2/3 | T3.5 | 113.4° | 504 | Add ND 0.20 (nearest ND 0.3 · ND2) |
| +1/3 | T3.2 (exact T3.14) | 142.9° | 635 | Add ND 0.10 (nearest ND 0.3 · ND2) |
| −1/3 | T2.5 | 226.8° | 1008 | Remove ND 0.10 (nearest ND 0.3 · ND2) |
| −2/3 | T2.2 | 285.7° | 1270 | Remove ND 0.20 (nearest ND 0.3 · ND2) |
| −1 | T2 | 360° | 1600 | Remove ND 0.3 (ND2) |
| −2 | T1.4 | 720° | 3200 | Remove ND 0.6 (ND4) |
ND filters: stops, density and markings
| Stops | Density | Marking | Light through |
|---|---|---|---|
| 1 | 0.3 | ND2 | 1/2 |
| 2 | 0.6 | ND4 | 1/4 |
| 3 | 0.9 | ND8 | 1/8 |
| 4 | 1.2 | ND16 | 1/16 |
| 5 | 1.5 | ND32 | 1/32 |
| 6 | 1.8 | ND64 | 1/64 |
| 7 | 2.1 | ND128 | 1/128 |
| 8 | 2.4 | ND256 | 1/256 |
| 9 | 2.7 | ND512 | 1/512 |
| 10 | 3.0 | ND1024 | 1/1024 |
Shutter angle as a shutter speed
| Angle | At 24 fps | At 25 fps | At 30 fps |
|---|---|---|---|
| 45° | 1/192 s | 1/200 s | 1/240 s |
| 90° | 1/96 s | 1/100 s | 1/120 s |
| 144° | 1/60 s | 1/62.5 s | 1/75 s |
| 172.8° | 1/50 s | 1/52.08 s | 1/62.5 s |
| 180° | 1/48 s | 1/50 s | 1/60 s |
| 270° | 1/32 s | 1/33.33 s | 1/40 s |
| 360° | 1/24 s | 1/25 s | 1/30 s |
Save, share and get the Pro tools in the CineMath app
CineMath is a free download for iPhone, iPad and Mac, with this calculator built in. In version 1.3, coming soon to the App Store, CineMath Professional saves calculations to your history, shares them as links, and adds the Camera Database and Data Planning.
Questions
How do I work out exposure compensation in stops?
Each stop doubles or halves the light. To cut one stop, close the iris by one stop (multiply the T-stop by √2, about 1.41), halve the shutter angle, halve the ISO, or add an ND 0.3. To add a stop, do the opposite. One stop more light at T2.8, 180° and ISO 800 is T4, 90°, ISO 400 or an ND 0.3: any one of them.
How many stops is an ND 0.9?
Three. Every 0.3 of density is one stop, so ND 0.9 is three stops, marked ND8 because it lets through an eighth of the light. ND 0.6 is two stops (ND4) and ND 1.2 is four (ND16).
What shutter speed is a 180° shutter?
Half the frame interval: shutter speed = angle ÷ (360 × frame rate). At 24 fps, 180° is 1/48 s; at 25 fps it is 1/50 s; at 30 fps it is 1/60 s. 172.8° at 24 fps is exactly 1/50 s.
What does a positive EV change mean here?
More light has reached the sensor, so the calculator cuts it: it closes the iris, narrows the shutter, lowers the ISO or adds ND. A negative change means light was lost; the calculator opens up, widens the shutter, raises the ISO, or suggests removing ND (which assumes a filter is in).
Why does a third of a stop show "ND 0.10 (nearest ND 0.3 · ND2)"?
A third of a stop is 0.1 of density, but the filter list starts at one stop (ND 0.3). The calculator shows the exact density you need and the nearest filter in the list, so you can reach for an ND 0.1 if you carry one, or compensate with the iris instead.
Why does the calculator say a shutter angle is not achievable?
It flags any shutter angle outside 1–358°. Opening up one stop from 180° needs 360°, which it flags, and two stops would need 720°, which no camera shutter has. Use the T-stop, ISO or ND answer instead.