To blend a long exposure in Photoshop, stack two frames of the same scene, add a layer mask to the top one, and work with a soft black or white brush to reveal only the parts you want. This keeps smooth water or clouds from the slow frame and sharp detail from the quick one.
What You Need Before Blending
Blending works best when both frames share the same composition. Shoot from a tripod with the same focal length and framing, and keep focus and white balance consistent. Take one frame at a normal speed for sharp detail, and one with a slow shutter, often several seconds or longer with a neutral density filter, for smooth motion.
- Shoot raw so you can match exposure and color later.
- Use a tripod and, if possible, a remote or timer to avoid shake.
- Keep the camera in the same position between both frames.
Step by Step: Masking the Two Frames
- Open both raw files with matching basic settings, such as the same white balance and a similar tone curve.
- Open them as layers in one document. In Lightroom, select both and use the edit in Photoshop as layers command.
- Place the long exposure on top and the sharp frame below.
- If the frames do not line up exactly, select both layers and use auto-align layers.
- Select the top layer and click the add layer mask button. A white mask shows the whole layer.
- Invert the mask with Ctrl or Cmd plus I so it turns black and hides the top layer.
- Choose the brush tool, set the color to white, and use a soft edge at moderate opacity, roughly 30 to 60 percent as a baseline.
- Brush over the water, clouds or other moving areas to reveal the smooth exposure.
- Press X to swap to black when you need to hide the top layer again and fix mistakes.
- Zoom in at the edges and clean up any halos near rocks, trees or buildings.
Tips for Natural Results
Look at the transition zones, such as where waves meet rocks. A hard edge can look cut out, so lower brush hardness there. For complex shapes, make a selection first with a quick selection or sky selection tool, then convert it into a mask and refine it with a small brush.
You can also use a gradient on the mask for skies. Drag a black to white gradient across the mask to fade the long exposure in smoothly toward the horizon.
Common Problems
| Issue | Likely fix |
|---|---|
| Bright halo along edges | Lower brush hardness and brush inward |
| Different brightness between frames | Match exposure in the raw step |
| Ghosting in the sky | Run auto-align layers or mask the area out |
FAQ
Do I need two separate exposures?
Not always. Some photographers use a single slow frame and mask in a sharper element, but two frames give more control over moving subjects.
Should I use a smart object?
It can help. Converting layers to smart objects before filters keeps changes editable, though file sizes will grow.
The Short Version
Align two frames, put the long exposure on top, and use an inverted mask with a soft white brush to reveal motion. Keep edges soft and clean them at high zoom. Treat the brush settings as a baseline and adjust them to your scene.
