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Simulating Long Exposures in Photoshop Using Short Exposure Stacks

May 10, 2025 JimK Leave a Comment

Long exposures can produce beautifully smoothed water, streaked clouds, and motion blur that adds atmosphere and drama. But shooting long exposures in-camera isn’t always ideal: ND filters may introduce color casts, hot pixels can accumulate, and a gust of wind can ruin a single frame.

A practical alternative is to simulate a long exposure by stacking multiple short exposures in Photoshop. There are two key advantages to stacking short exposures. When you average multiple short exposures, random noise cancels out, effectively improving signal-to-noise ratio without needing a long exposure sensor readout. In addition, Each short exposure can be: a) reviewed for sharpness, motion, or artifacts, b) Replaced if there’s a problem (e.g., someone walked through the frame), and c) individually edited or masked before blending

He’s how you do it

Step 1: Shoot a Sequence

  • Use a tripod.

  • Capture a sequence of exposures at consistent settings (e.g., 1/10 sec x 100 frames).

  • Manual exposure mode and fixed white balance are recommended.

Step 2: Process in Lightroom

  • Apply global adjustments (white balance, exposure, lens corrections) to one frame.

  • Sync those edits to all frames.

Step 3: Export as Layers to Photoshop

  • Select all the frames in Lightroom.

  • Right-click → Edit In > Open as Layers in Photoshop.

Step 4: Convert to Smart Object

  • In Photoshop, select all layers.

  • Right-click → Convert to Smart Object.

Step 5: Apply Stack Mode

  • Go to Layer > Smart Objects > Stack Mode, and choose:

    • Mean: For natural averaging; good for smoothing noise and motion.

    • Median: For rejecting outliers (e.g., moving people, cars); ideal for “ghost removal.”

Creative Applications

  • Simulate ND effects (cloud streaks, water blur).

  • Remove moving objects (cars, crowds).

  • Reduce noise by averaging.

  • Maintain full control over frame-by-frame editing, dodging, or alignment.

Tips

  • For cleaner results, use anintervalometer to minimize camera shake.

  • Ensure alignment is tight—use Photoshop’s auto-align feature if necessary.

  • Consider blending foreground and background separately for better control of motion blur.

  • If you’re doing things like star trails, make your basic exposure long enough that you won’t see gaps.

Simulating long exposures in Photoshop gives you more flexibility than an in-camera approach. It’s a great technique to have in your photographic toolkit.

The Last Word

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