Exposure planner
Enter your camera and filter settings
Start with a meter reading made without dark filters. The calculator adjusts it for aperture, ISO, filter stops, reciprocity correction, and a practical safety buffer.
Reference examples
Example exposure data
| Metered setup | Target setup | Filter loss | Calculated time |
|---|---|---|---|
| 1/125 sec, f/8, ISO 100 | f/8, ISO 100 | 10 stops | 8.19 seconds |
| 1/60 sec, f/8, ISO 100 | f/11, ISO 100 | 6 stops | 2.02 seconds |
| 1/30 sec, f/4, ISO 400 | f/8, ISO 100 | 3 stops | 4.27 seconds |
| 2 seconds, f/8, ISO 100 | f/8, ISO 100 | 13 stops | 4 h 33 m 4 s |
Calculation method
Formula used
Each added filter stop halves incoming light. The shutter time must therefore double. Aperture changes use the square of the f-number ratio. ISO changes use the original ISO divided by the chosen ISO.
The reciprocity control is optional. A multiplier scales the computed time directly. An exponent raises the calculated seconds to your tested correction value. Use those settings only when you have a trustworthy reference for your camera or film.
Practical steps
How to use this calculator
- Meter the scene without a dark neutral density filter.
- Enter that shutter time, aperture, and ISO as the base setup.
- Enter your selected aperture, ISO, and every filter loss.
- Apply reciprocity correction only when your testing supports it.
- Add a small buffer when light may change during setup.
- Calculate the time, set a timer, then review your histogram.
Photography guide
Planning Long Exposure Photography
Long exposure photography makes time visible. Moving water can appear soft. Clouds may stretch across the frame. Traffic can form bright lines. The scene still needs a correct exposure. A meter reading gives a starting point. It does not automatically include dense filters. This calculator turns the reading into a practical shutter time.
Start With a Reliable Meter Reading
Begin with a clean reference exposure. Meter the scene without your neutral density filter. Record the shutter time, aperture, and ISO. Keep the framing fixed. Focus before installing a very dark filter. Switch to manual focus afterward. This prevents the camera from hunting. Use a solid tripod. Small vibrations can soften a long exposure. Disable unstable accessories. Shield the camera from wind when possible.
Understand Filter Stops
Neutral density filters reduce incoming light. Each full stop halves that light. The camera therefore needs twice as much time for every added stop. A six-stop filter needs sixty-four times the original exposure. A ten-stop filter needs one thousand twenty-four times the original exposure. Stacking filters adds their stop values. A polarizer can also reduce light. Add its measured loss to the total.
Include Aperture and ISO Changes
Changes to aperture and ISO matter too. A larger f-number passes less light. The time changes by the square of the f-number ratio. Moving from f/8 to f/11 now needs nearly twice the time. Lowering ISO also needs a longer exposure. Changing ISO 400 to ISO 100 needs four times more time. The calculator includes both changes. This avoids mental mistakes during low-light work.
Use Compensation Carefully
Very long times may produce reciprocity failure. Film often needs special correction. Some digital sensors can show extra noise or hot pixels. Camera behavior differs by model. Test your equipment before important work. Use the optional compensation controls only when your testing or manufacturer guidance supports them. A small safety buffer can help when light changes. It cannot replace good judgement.
Time the Exposure Well
Use Bulb mode when the needed time exceeds your camera limit. An intervalometer helps with accurate timing. Cover the viewfinder on certain cameras. Enable long-exposure noise reduction only when its extra processing time is acceptable. Review the histogram after the first frame. Check highlights, not only the preview brightness. Adjust exposure slowly. Preserve bright lamps and reflective water.
Build a Repeatable Workflow
Long exposure work rewards preparation. Arrive early and watch the light. Compose while it remains easy to see. Set focus and stabilization carefully. Then calculate, expose, and review. Make notes about filters and actual results. Those notes make future calculations faster. Consistent tests turn a useful estimate into a reliable personal workflow.
Weather changes can alter a calculated result. Recheck the meter after sunset, cloud movement, or changing city lights. Keep spare batteries warm. Long timers drain power. Carry a cloth for lens spray. Patience helps every exposure.
Common questions
Long exposure FAQs
1. What is a long exposure?
It is a photograph made with a deliberately extended shutter time. The longer time records motion across the frame. Water, clouds, stars, and moving lights can show creative blur while stationary objects remain sharp.
2. Why does every ND stop double the time?
One stop means half as much light reaches the sensor or film. To keep the same exposure, the shutter must stay open twice as long. Two stops need four times the original time.
3. Can I stack neutral density filters?
Yes. Add their stop values together. A six-stop filter plus a three-stop filter creates nine stops of loss. Check for vignetting, reflections, color casts, and reduced sharpness before using stacked filters for important work.
4. Why does changing aperture alter exposure time?
The f-number describes the opening relative to focal length. Higher f-numbers pass less light. Time changes by the square of the aperture ratio, so the effect is larger than a simple linear change.
5. How does ISO affect the result?
Lower ISO values need more light for the same brightness. Moving from ISO 400 to ISO 100 needs four times more exposure. The calculator uses the metered ISO divided by the selected ISO.
6. When should I use Bulb mode?
Use Bulb mode when the calculated shutter time is longer than your camera’s normal maximum setting. An intervalometer or remote timer makes those longer exposures easier to start and stop accurately.
7. What is reciprocity correction?
Some film materials respond less efficiently during very long exposures. They may need more time than the standard formula predicts. Digital cameras vary too. Use custom compensation only after testing or consulting reliable camera-specific guidance.
8. Does a polarizer affect long exposure time?
Yes. A polarizer reduces light, often by about one to two stops. Its exact loss can vary. Enter the measured or manufacturer-stated stop loss, then include it with your neutral density filter strength.
9. Should I include a safety buffer?
A small buffer can be useful when clouds or twilight change rapidly. It is optional. Start with zero for controlled conditions. Use a modest percentage only when your experience suggests the scene may become darker.
10. Why should I review the histogram?
The rear screen can look brighter or darker than the final file. A histogram helps reveal clipped highlights and deep shadows. Review the first image, then adjust the time based on the data and your intended look.
11. What should I do after the first frame?
Review the histogram and highlights. Compare the frame with your creative goal. Adjust the shutter time in small steps. Capture calm scenes, then create memorable long exposure photographs.