Long exposure photography is usually associated with low light. Nighttime light trails, dim waterfalls at dawn, star trails after dark. But the most dramatic long exposure subjects are often in broad daylight: crashing ocean waves, rushing rivers, fast-moving clouds over mountains.
The problem? Too much light.
Why Daytime Long Exposure Is Hard
A traditional camera creates long exposure by keeping the shutter open for seconds. In bright daylight, this floods the sensor with light and overexposes the image to pure white. Photographers solve this with ND (neutral density) filters, which are essentially sunglasses for the lens. A 10-stop ND filter reduces light by 1000x, allowing a 10-second exposure in full sun.
iPhones do not have filter threads. You can buy clip-on ND filters, but they are often low quality, cause vignetting, and add bulk to a device designed to fit in your pocket.
The Computational Solution
Frame stacking sidesteps the problem entirely. Instead of one long exposure, it captures many short exposures (each at 1/30th of a second, properly exposed for daylight) and blends them together. The result is identical to a long exposure, but each individual frame is correctly exposed.
This is why you can shoot silky water in full sun on an iPhone without any filters. The app handles the light management for you.
Best Daytime Subjects
Waterfalls and Rivers
The classic long exposure subject. Running water at 5 to 15 seconds becomes smooth silk. Faster water (rapids, spillways) needs shorter durations. Slow streams need longer. Start at 5 seconds and adjust based on the preview.
Ocean Waves
Waves crashing on rocks or rolling onto a beach produce misty, ethereal results with 10 to 30 seconds of capture. The receding foam becomes smooth gradients. Rocks and sand stay sharp.
Clouds
On a windy day, clouds move fast enough to streak across the sky in 30 to 60 seconds. The effect works best with dramatic cloud formations (cumulus, alto). A flat overcast sky produces a featureless white blur, which is less interesting.
Busy Streets and Crowds
Pedestrians become ghostly blurs while buildings stay sharp. At 15 to 30 seconds with steady foot traffic, most people disappear entirely (median blending) or become transparent streaks (mean blending).
Fountains and Sprinklers
Water in motion is always a good subject. Fountains at 3 to 10 seconds produce smooth, continuous arcs instead of frozen droplets.
Settings for Daytime
ISO: As low as possible. ISO 50 or 100 keeps each frame clean and avoids overexposure in bright conditions.
Mode: Smooth (mean blending) for water, clouds, and motion blur. Ghost Remove (median blending) if you want to erase moving people completely.
Duration: Depends on subject speed. Fast water: 3 to 10 seconds. Slow clouds: 30 to 60 seconds. Crowds: 15 to 45 seconds.
Stability: Handheld works for short captures (under 10 seconds) if you brace against something. For anything longer, use a tripod or a stable surface.
The Advantage Over Traditional ND Filters
Beyond not needing extra hardware, frame stacking has a technical advantage in daylight: each individual frame is properly exposed and sharp. With an ND filter, you are still shooting one continuous exposure, so any vibration during those 10 seconds affects the entire image.
With stacking, if your hand shakes slightly during one frame out of 300, it barely affects the final blend. The other 299 sharp frames dominate. This makes handheld daytime long exposure surprisingly viable.
The one thing ND filters still do better: they create genuine optical motion blur with a continuous, perfectly smooth gradient. Frame stacking produces a very close approximation (capturing at 30fps means 30 discrete samples per second), but at normal viewing sizes, the difference is invisible.
Quick Start
- Find a subject with motion: water, clouds, people, traffic.
- Open Lento, select Smooth mode, set ISO to the lowest value.
- Brace your phone or use a tripod.
- Tap shutter and watch the preview smooth out in real-time.
- Stop when the motion blur looks right. Export.
No filters. No editing. No post-processing. Just point, capture, and export.