Introduction
The gaffer just dimmed the key light by 2 stops for a moodier take, and the DP wants to compensate without changing the depth of field look you've spent 20 minutes dialing in. You can't open the aperture. You need to find the exact ISO and shutter combination that adds 2 stops of exposure while keeping the lens at f/4. That's an equivalent exposure problem.
The equivalent exposure calculator takes your current aperture, shutter speed, and ISO, then shows every combination of settings that produces the same brightness. Change one parameter and see all the options that compensate for it, complete with notes on depth of field, motion blur, and noise tradeoffs.
This tool eliminates the mental arithmetic of stop-counting and lets you make informed creative decisions about which parameter to sacrifice when the light changes.
What This Tool Calculates
The calculator accepts your current exposure triangle settings: aperture (f-stop), shutter speed, and ISO. You then select which parameter you want to vary.
It returns a table of all equivalent exposure combinations that maintain the same brightness (same EV value). Each row shows the aperture, shutter speed, and ISO for that combination, plus practical notes about depth of field depth, motion blur risk, and noise level. The original settings are highlighted for reference.
The Formula and How It Works
Equivalent exposures share the same exposure value (EV). The EV formula is: EV = log2(N squared / t) minus log2(ISO / 100), where N is the f-stop and t is the shutter speed in seconds.
Any combination of N, t, and ISO that produces the same EV delivers the same image brightness. Each full stop change in one parameter requires a compensating 1-stop change in another. Opening the aperture by 1 stop (e.g., f/5.6 to f/4) doubles the light. Doubling ISO (e.g., 400 to 800) also doubles sensitivity. Halving the shutter speed (e.g., 1/125 to 1/60) doubles the exposure time.
Worked example: starting at f/4, 1/60s, ISO 400. To maintain the same brightness at f/2.8 (1 stop wider), you need to compensate by removing 1 stop elsewhere. Either increase shutter speed to 1/125 (1 stop faster) or halve ISO to 200. Both combinations produce identical brightness.
Real-World Examples
Preserving Depth of Field During a Lighting Change
A DP shooting an interior dialogue scene at f/4, 1/48s, ISO 800 received word from the gaffer that the key light was dropping 2 stops due to a dimmer adjustment for mood. The DP wanted to keep f/4 for consistent depth of field across the scene. Using the equivalent exposure calculator, the team found that bumping ISO from 800 to 3200 (2 stops) maintained the same brightness at f/4, 1/48s. The DIT confirmed the noise level at ISO 3200 was within the camera's clean range.
Switching from Daylight to Golden Hour Without Stopping
A commercial shoot needed continuous takes from full daylight into golden hour. The starting exposure was f/8, 1/48s, ISO 200. As light dropped, the DP needed equivalent exposures that maintained the 180-degree shutter. The calculator showed the progression: f/5.6 at ISO 200, then f/4 at ISO 200, then f/4 at ISO 400, then f/2.8 at ISO 400. Each step preserved brightness while the DP chose the tradeoff between depth of field and noise.
Converting a Photography Exposure to Cinema Settings
A DP scouting a location took a test photo at f/2.8, 1/500s, ISO 100. On the shoot day using a cinema camera locked at 1/48s shutter (180-degree rule), they needed the equivalent exposure. The calculator showed that 1/500 to 1/48 is roughly 3.4 stops slower shutter, requiring 3.4 stops less light elsewhere. The equivalent was f/8, 1/48s, ISO 100, or f/5.6, 1/48s, ISO 50 (if the camera supported it).
Equivalent Exposures at EV 10 (ISO 100 base)
| Aperture | Shutter Speed | ISO | Notes |
|---|---|---|---|
| f/1.4 | 1/4000 | 100 | Very shallow DoF, frozen motion |
| f/2 | 1/2000 | 100 | Shallow DoF, fast shutter |
| f/2.8 | 1/1000 | 100 | Moderate DoF, sharp motion |
| f/4 | 1/500 | 100 | Standard DoF, standard shutter |
| f/5.6 | 1/250 | 100 | Deeper DoF, moderate blur |
| f/8 | 1/125 | 100 | Deep DoF, slight motion blur |
| f/11 | 1/60 | 100 | Very deep DoF, handheld limit |
| f/16 | 1/30 | 100 | Maximum DoF, tripod recommended |
Pro Tips and Common Mistakes
Pro Tips
- In cinema, lock your shutter speed first (1/48s for 24fps). Then the equivalent exposure table reduces to aperture vs. ISO tradeoffs only, making decisions much simpler on set.
- When the DP calls for a lighting change, check the equivalent exposure table before moving any lights. Often, a 1-stop ISO bump achieves the same result as repositioning a 12K HMI, saving 20 minutes of setup time.
- Use the notes column to anticipate problems. If an equivalent setting shows 'motion blur risk' or 'high noise,' you know that combination has a creative cost even though the brightness is identical.
- Print the equivalent exposure table for your planned EV range before the shoot day. Hand it to the 1st AC and DIT so everyone can reference the same numbers when conditions shift.
Common Mistakes
- Forgetting that equivalent exposure only matches brightness, not the look of the image. f/2 at 1/250 and f/8 at 1/15 produce the same brightness but radically different depth of field and motion blur. Always evaluate the creative side effects.
- Changing two parameters and assuming they cancel out without checking the math. Opening 1 stop of aperture and closing 1 stop of ISO does cancel out. But opening 1 stop of aperture and slowing shutter by 1 stop adds 2 stops of light, not zero.
- Not accounting for your camera's native ISO. Some cameras (like the ARRI ALEXA 35 at ISO 800) have a base sensitivity that produces the cleanest image. Moving away from native ISO in either direction can reduce dynamic range or add noise.
Frequently Asked Questions
What is an equivalent exposure?
An equivalent exposure is any combination of aperture, shutter speed, and ISO that produces the same image brightness as another combination. If you change one setting, you can compensate with another to maintain identical exposure. The exposure value (EV) number stays the same across all equivalent combinations.
How many stops is one full change in aperture, shutter, or ISO?
One full stop doubles or halves the light. For aperture, the full-stop sequence is f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22. For ISO, it doubles: 100, 200, 400, 800, 1600. For shutter, each doubling of speed is one stop: 1/30, 1/60, 1/125, 1/250, 1/500.
Why would I use equivalent exposure instead of just using auto exposure?
Auto exposure chooses settings based on brightness alone and ignores creative intent. A cinematographer needs to control depth of field, motion blur, and noise independently. Equivalent exposure lets you pick the creative parameters first and then find the matching technical settings that deliver correct brightness.
Does equivalent exposure work the same for video and photography?
The math is identical. The difference is that video typically locks shutter speed (180-degree rule), reducing the triangle to two variables. Photographers can freely adjust all three. The calculator works for both workflows by letting you choose which parameter to vary.
Start Calculating
Equivalent exposure is the skill that separates operators from cinematographers. Knowing that f/2.8 at 1/1000 and f/8 at 1/125 produce the same brightness but completely different images is the foundation of intentional visual storytelling.
Set your current exposure above and explore every equivalent combination. Which parameter do you prioritize when the light changes on set, and which one do you sacrifice last?
