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Multiple exposures can be used for several purposes. Well-known reasons for making multiple exposures include the creation of a panorama, focus stacking and creating high dynamic range (HDR) photos. But what not so many people know is that multiple exposures can also be stacked in Photoshop to reduce noise or to extend the effective exposure time. In this article I will explain the use of stacking multiple exposures to increase the effective exposure time.

The first step consists of taking multiple photos. For the example that I consider here, I used a 9-stops ND filter, such that the exposure time of a single photo was 10 s. I took many photos with the same camera settings and I stacked in the end 32 of them.

Once you have processed your photos in Camera RAW or Lightroom, the next step is to open the photos into Photoshop as layers. A way to do that is through Adobe Bridge: select the photos in Bridge and in the menu go to Tools – Photoshop – Load Files into Photoshop Layers.

Open files as layers in Photoshop

All photos loaded as layers in Photoshop

In Photoshop, select all the layers and create a smart object. 

Convert to a smart object

Once you have combined all layers into a smart object, render a single image based on all the layers by selecting stack mode ‘mean’.

Select stack mode 'mean'

This stack mode creates a nice and smooth image with an effective exposure time of all photos combined.

Result of stack mode 'mean'

In this case I used 32 images, each with an exposure time of 10 s, so the total effective exposure time was 320 s. 32 images corresponds to 5 stops (2^5 = 32). This means that effectively the stacked image has an exposure time as if a 14 stops filter would have been used: 9 stops from the actual ND filter that I used, plus 5 stops from stacking.

In summary: if you don’t have an ND filter with many stops or if you want to increase your effective exposure time even more, stacking multiple exposures is a great way to do so.

I further processed the stacked image in Photoshop by cropping it and adjusting contrasts and colors. The end result is shown below.

Single shot

Final image

  • Martin Podt

    on February 22, 2022

    Thanks, Sophie. All photos are made with the same settings. Indeed the only difference is in the sky and the water.

  • Sophie Carpene

    on February 20, 2022

    Hi Martin , thanks for sharing your pictures and your knowlege / May I ask a question ? You say that you take 30 pictures with the same setting . Are the only difference between the pictures the sky or the water ? Or do you change each time some value ? Thanks for your answer. Best regards

  • Martin Podt

    on June 7, 2020

    Thank you. I use a tripod, such that there is no movement. But if there is some movement, you can align the different shots in Photoshop before the stacking.

  • Vinay Chiru

    on June 7, 2020

    Hello Sir,
    How do u manage if there are minor movements or shakes in few of the images. Will u fix the halo first ? or will the stacking take care of it while using it with the option "mean" ?

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