How To Improve Your Long Exposure With Photo Stacking

How to Improve Your Long Exposure Photography with Photo Stacking

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Recently long exposure photography has been quite popular, mainly in the landscape photography arena. One of the reasons (among the others) is that through a long exposure it is possible to visualize a scene with much more softness and harmony in respect to a standard exposure.

Thanks to the rapid evolution of digital cameras, we are now able to take really long exposures without getting so much digital noise, due to sensor overheating. Moreover, the improvements in neutral density filter quality allow us to take pictures with almost no color cast, and no decrease in sharpness.

Dps les venezia

Venezia by Luca Libralato: stacking of 3 x 260s exposures for a total of 780s (13 minutes)

If you love long exposure photography and you would like to push the exposure time to the edge, this technique of long exposure photo stacking is for you.

Here is the quick explanation of the Long Exposure Stacking technique: by taking several pictures (usually at least 30 seconds each for the purpose of this technique) you can blend them to get a result the equivalent of a long exposure photo with a total exposure time equal (or almost equal) to the sum of the single exposure frames.

This technique is mostly useful, and recommended for landscape photography, but some of the benefits may also be used in other types of photography, where you need maximum quality with several minutes of exposure. The step by step guide will be focused on landscape photography.

The advantages of using this approach are several:

  • Increase the total exposure time.
  • Reduce digital noise and hot pixels (shorter exposure pictures have less digital noise and hot pixels).
  • Reduce vignetting (you will be using a lower ND power per shot with this technique, resulting in less vignetting).
  • Minimize the risk of wasting time and photos (tripod shocks, sudden light change, etc.).
  • Possibility to decide later on the strength of the long exposure effect.
dps_les_manarola

Manarola by Luca Libralato: stacking of 3 x 260 second exposures for a total of 780 seconds (13 minutes)

The disadvantages are:

  • You don’t have a single exposure and this is something which some competitions/contests rules don’t like.
  • Some post-processing skills are required to blend the several exposures.
  • If you are a purist – you may not like this technique.

When this technique should be used:

  • If you want to push the exposure time to some really high values.
  • If your camera sensor is adding a lot of digital noise due to overheating.
  • If you are not sure about the final result of a very long exposure. Since this techniques is based on the sum of several short exposures, you can easily decide later how long the final exposure shall be (check also here for a similar approach: Long Exposure Photography Without a Tripod).
  • With hostile ambient/weather conditions, you can use this technique to minimize the risk of wasting exposure time.
  • If you want to maximize the probability to not miss the right moment in a fast changing light (the right moment can last few seconds, if you are exposing for several minutes, you can miss it for wrong exposure time for example).

Before going over the explanation of the technique, there are at least a couple of required skills you should have (apart from the basics for taking pictures with your camera):

  1. How to perform standard long exposure photography: you can check this awesome tutorial by Francesco Gola to improve your long exposure skills: Step-by-step Guide to Long Exposure Photography.
  2. Basic knowledge of Adobe Photoshop or similar photographic software which allows you to work on images using layers.

Let’s get on with the fun part: the implementation of Long Exposure Stacking!

dps_les_punta_aderci

The Magic Of Punta Aderci by Luca Libralato: stacking of 2 x 260 second exposures for a total of 520 seconds (8:40 min)

Step 1: Gear

The photographic gear needed for this technique is luckily the same gear needed for taking long exposure photos. So if you are already familiar with long exposure photography, you are set. Otherwise here is a short list of all the tools:

  • Digital Camera (which allows long exposure) + Lens (which allows you to mount neutral density filters)
  • Tripod
  • Remote trigger (optional, but suggested)
  • Neutral density filters (optional if you shoot when it’s dark)

For further details about taking long exposure photography, you can check the related resources listed at the bottom of the article.

Step 2: Plan the shot

Never hit the shutter without having properly planned the photo. Of course there are a lot of variables involved, but planning can really play the most important part in a good photo. Do not underestimate the power of accurately planning a landscape photo – because luck can help you once, but planning your photography consistently, will increase the probability that you’ll be ready when the right conditions are present.

dps_les_santa_marinella

Rips Of Darkness by Luca Libralato: stacking of 5 x 120 second exposures for a total of 600 seconds (10 minutes)

Step 3: Take the shots

Once you have planned your photo and you are on location, you should then decide the two most important things in any photo (at least this kind of photo): composition and exposure (supposing you are taking landscape photography, depth of field should not be a variable in most cases). Composition is up to your taste, while exposure is a complex matter and depends upon different factors.

First thing every landscape photographer usually does before taking any picture, is metering the light to decide the exposure time. The final exposure time depends on several factors, such as strength of the wind, the movement of the clouds, water flow, and so on. The question at this point is, “How long shall I expose for?”.

If the light is changing suddenly, or there is a strong wind which can shake your camera/tripod during exposure, you may decide to avoid really long exposures (to avoid wasting shots or missing the right light). This is where this technique comes to your rescue.

Suppose you would like to have a total of eight minutes of exposure, instead of taking one single long exposure file you can split the total exposure time into four consecutive shots of two minutes each (for example). You can freely decide the final length of each exposure and the total number of shots, just keep in mind that you should keep the gap of time between the different photos to a minimum, if you are planning to do stacking. Needless to say that you should be careful in avoiding moving the tripod and the camera between each shot of the sequence. Once you have your consecutive shots, in the next step you will understand what to do in post-processing.

Before you start shooting: make sure you focused correctly and your tripod is stable (avoid sand or uneven floors where possible).

After the shot: make sure your histogram is fine and your picture is properly exposed, or exposed to the right.

Dps les 01 Dps les 02
Dps les 03 Dps les 04
Dps les 05 Dps les 06

Arco Della Pace by Luca Libralato: 6 x 130 second exposures, for a total of 780 seconds (13 minutes)

Step 4: Image Stacking

You should now be at home, or in your favourite cafe/pub with your laptop, and hopefully a coffee/beer. You should have downloaded all of your shots and selected the ones you would like to stack.

The stacking process will be shown for Adobe Photoshop (almost any version supports the feature) but you can use any software of your choice, which allows the use of layers. In Photoshop there are two different methods that can be used to stack files, with the goal to merge them into a simulated longer exposure:

  1. Load files into stack function (Files > Scripts > Load Files into Stack)
  2. Manual stacking

4.1 Load files into a stack

With the first method the procedure is semi automated, since you just need to go to Files > Scripts > Load Files into Stack

Dps les ps stack 01

Photoshop: Load Files into Stack

All you have to do is then select the single long exposure, flag the boxes to Automatic Align Source Images and Create Smart Object.

Dps les ps stack 02

Photoshop: Select files and create Smart Object

Once you have a new document with the Smart Object selected, all you have to do is go to menu Layer > Smart Objects > Stack Mode > Mean. This will weigh all images embedded into the Smart Object, rendering them as a new image which similar to what you would have obtained with a single long exposure of a total time equal to the sum of the single exposure.

Dps les ps stack 03

Photoshop: Set Stack Mode to Mean

You can check the result on the image below.

Dps les ps stack result

Photoshop: Result after stacking

4.2 Manual stacking

By using the second method (which I trust can be used with every software which allows layers) the blending process is manual. The rule is that you have to fine tune the opacity of each layer by decreasing it after each shot.

The mathematic rule is as follows: each shot should have an opacity equal to 1 divided by its position in the stack. Here is a table which shows the rule:

  • First photo (the one at the bottom) 100% (1/1)
  • Second photo 50% (1/2)
  • Third photo 33% (1/3)
  • Fourth photo 25% (1/4)
  • Fifth photo 20% (1/5)
  • Sixth photo 17% (1/6)
  • Nth photo 1/N

This process will exactly replicate the first method (the result will be identical to an automatic Stack in Mean mode).

Step 4: Post processing workflow

At this point, all you have to do is follow your typical post-processing workflow:

  • Clean dust spots, straighten the image, crop
  • Adjust dynamic range with other exposures (3 or 5 bracketing shots for static underexposed parts)
  • Adjust exposure and contrasts
  • Adjust colors
  • Add finishing touches to suit your taste
  • Export

Here is the final result of the example

Dps les arco della pace

Arco Della Pace by Luca Libralato: stacking of 6 x 130 second exposures for a total of 780 seconds (13 minutes)

Conclusions

This technique is very useful sometimes because of its flexibility. Moreover you should consider the benefit in increasing the final quality of your file because of the stacking. It has been proven that by stacking images you can benefit by reduction in random digital noise equal to the square root of the total photos used. So for example if you use four photos, you will have in static part of the photo a reduction by half of the total random digital noise, which is a great achievement especially for underexposed portions. This technique is used a lot (even if with some different variations and implications) in astrophotography or in other fields when increasing the exposure time of a single shot is not suitable.

Don’t hesitate to ask questions in the comments box below if you need help or further explanations.

Related Resources:

Read more from our Post Production category

Luca Libralato is an Italian landscape photographer who loves technology and coding. Born in Latina (near Rome) in 1974, he started taking photos of seascape and natural parks near home. As soon as he bought his first neutral density filter, he suddenly fell in love with long exposure photography. Luca states that long exposures allow him to relax, and at the same time give him the opportunity to provide a different vision and mood of places. See more of his work on 500px or his website or join one of his workshops!

  • Great article!

  • Evgeniy

    I wonder if there is a general rule to determine the best number of shots? For example, for 780s result, should I take 6 photos of 130s each or, like, 12 photos 65s each?
    Also, I suppose it is somewhat different to stack photos in various orders. You’re working in sunset time and every shot will be a little lighter than the previous one, and by choosing layers’ orders the result will tend to be more brighter or darker, right?

  • Hi Evgeniy,
    it really depends on your taste and your goals.

    Regarding your first question “number of shots”, I would say that it depends on two factors, quality of light and total exposure you want to achieve. If light is good you can easily go for a longer exposure, since you will get lower noise… this means also less shots, because you won’t need stacking to reduce noise. If wind is strong for example, you don’t need to take really long exposure and you can decrease the total number of shots. Usually you need an higher number of shots if quality of light is low (low light and fast changing conditions) and when wind is slow… Let me know if it’s clear. 🙂

    Regarding the order, if you average the shots, it doesn’t matter switching the order of photos while stacking, the result should be identical. Have a try and let me know. 🙂

    Anyway you got an important point, if you keep exposure time fixed (I often use 128s or 256s) during sunrise or sunset, you will get increasing or decreasing light… and this will help you in getting a natural high dynamic range while taking long exposure. Sometimes if you use this technique exactly during sunrise and sunset you may get 2 or 3 f/stop of difference betweeen the first and the last shot, I often mix different light (always from consecutive shots, I don’t mix different times of the day) to improve dynamic range (by averaging light).

  • Thank you Maria

  • Thanks for the great tips! I love some of your images! I defiantly agree with taking multiple shots and then stacking them later.

    NVeal
    http://www.solihullphotography.com

  • Thank you very much. 🙂

  • Evgeniy

    Thanks for the answer Luca. It is really only the first-hand experience that will help understand all effects offered by this technique. We have autumn here in northern hemisphere and I’ll definitely make several photo sessions and then play with results.

  • Lori Haynes

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  • Terry D.

    I missed what ND filter to use? an ND10 for daylight?

  • Hi Terry, it really depends on the scene you are capturing, so you should first meter the exposure time without filters, and then calculate how many f/stops you need to get to the desired long exposure time.

    Let’s say you are at f/11 and ISO 100 in Aperture priority… you can meter the exposure without filter and get the current exposure time, which we can suppose it’s 1/125.

    Now suppose you want to do a long exposure for 32s, then you are “missing” 12 f/stops to get there… in this case you can choose what to do:

    1. ND4000 (-12 f/stop)
    2. ND1000 (-10 f/stop) + ND4 (-2 f/stop)
    3. ND64 (-6 f/stop) + ND64 (-6 f/stop)
    4. ND1000 (-10 f/stop) + stop down to ISO 50 + step down to f/16

    There are several way to get the same result, it’s just up to you, depending on your goal and vision.

  • Terry D.

    Thank you for the detailed reply and clarification.

  • David

    Hi. Another quick and dirty solution is to change the ISO to 6400 leaving the same f stop and aperture. Note to have manual focus before a strong ND filter is applied. Take short shots and once you have the exposure approximately right then take the number of seconds and then have that the number of minutes at ISO100 eg 1second @ISO6400 = 1minute @ISO100. 0.5sec => 30 seconds etc. For very long exposures or fast changing light, then add or subtract as you see fit. Main thing is not to blow out the highlights but clipped blacks are generally more acceptable. YMMV

  • Frederic

    Great article, thank you!
    Could I ask for details about the HDR part and how you merged it with the long exposure?

  • Antonia Pagan

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  • Hi Frederic, I have just merged the three exposures as hdr and masked the static part of the photo… really easy in this case. Usually I prefer using luminosity masks now, but that photo is quite old and at that time I still used HDR Pro.

  • Declan Barrett

    For each long exposure , do you keep the focus the same or change it to different areas of the subject? Also, do you under or over expose for each different shot?

  • Frederic

    Thank you for your answer!

  • insertusername

    Thanks, great article! I love your photo called “Rips Of Darkness”

  • Thanks for share…it really depends on the scene you are capturing, so you should first meter the exposure time without filters, and then calculate how many f/stops you need to get to the desired long exposure time.

  • TByte

    More articles like this, please!

  • Any time you’re stacking images (unless you’re doing focus stacking) you need to keep focus the same. Maybe Luca can answer the second part for you.

  • Hi Declan,
    I only shot in hyperfocal, it’s very rare I do change focus… honestly I don’t see any reason to change focus with this technique, since your goal should be take a very long exposure. In a case where you need something on foreground on focus, you may want to take a single shot without filter and then mask it.

    Regarding over/under exposure, I usually shot at twilight without changing exposure time, to get natural under/over exposure, so I usually start with a darker shot at sunrise while I start with a brighter shot at sunset… as long as you get several photos, exposure will be naturally increased/decreased wheter you are shooting at sunrise/sunset.

    I hope everything is clear. 🙂

  • Thank you very much. 🙂

  • Okay, so let me make sure I’m understanding this correctly. This process isn’t using long exposure to get a properly exposed photo, where it is so dark that it takes a long shutter speed to get enough light. This process is for getting cloud and water movement in the photo for the “Silky” look, correct?

  • Declan Barrett

    Thank you

  • Vignesh Dhakshinamoorthy

    This article is very good and I liked it a lot, i went ahead and put it in action today at a nearby lake. It was a bright morning and I had my ND filter on, allowing me to take 6 8-sec exposures and stitched it together. It came out quite nice.
    https://www.facebook.com/vikkeephotography

  • In step 4.1, if one is using Photoshop CC and above, instead of “Edit > Smart Objects > Stack Mode > Mean,” it would be under “Layer > Smart Objects > Stack Mode > Mean.”
    I think that is what you meant if you look at your image capture in that step.
    Great article!!

  • You are correct… I’ll ask to fix it.

    Many thanks for reporting.

  • Hi Justin,
    the goal is to improve really long exposure photos. So you will find it useful only when you’d like to take pictures with an exposure of over 2 minutes…

    In any other case you can normally just take a single standard long exposure file without compromising quality.

  • kelsang jorlam

    can i make the image in three parts by using the “multi – exposure” setting in-camera?

  • What blending mode should be used when manually stacking the layers?

  • lilong

    For Nikon users http://igg.me/at/Pinout
    Let’s Pinout long exposure

  • KD

    Thanks for this article, very useful. Does this work with RAW images?

  • Ciao Luca nel photoshop in Italiano Mean a cosa corrisponde?
    Grazie

  • Ciao Massimiliano, dovrebbe corrispondere a MEDIA o MEDIO, da distinguersi verso MEDIANO o INTERMEDIO.

  • Hi, sure it works with RAW images, I always stack from RAW images. 🙂

  • If your camera supports “averaging exposure” method, it should work. I’d be happy to check the result if you do it.

  • Hi Joe, you should use normal blending. You just have to change the opacity level.

  • Well… it’s a bit spammy here… 🙂

  • Carlos Do Carmo

    Hello Luca, you have made this beautiful pictures with big stopper filters, right? I just ask it, because it´s impossible to take 120 sec. pics, without a big stopper filter.

  • Yes, using filters is almost a necessity when you want to increase exposure and it is not complete darkness.

  • Ciao Luca esiste una app per stabilire per esempio quanti scatti devo fare da 1/80″ per arrivare a 8′

  • Ciao Massimiliano, il calcolo è semplice, basta dividere 8/1/80, ovvero 640… il problema è che con un tempo così veloce questa tecnica probabilmente non avrebbe senso… è più il tempo che passerebbe tra uno scatto e l’altro che l’esposizione effettiva…

  • Don Cavalli

    So … I don’t have a CC or CS version of Photoshop yet. But I do have PSE 14. But I don’t see the Smart Objects in the pull down menu. Does this mean i can’t do it that way?

  • Hi,
    I don’t know how PSE works, but if you can set manually the opacity of each layer, you can do in that way: check paragraph 4.2 in the article.

  • Swapnil Sawant

    Hi, your images are stunning. they are just surreal. amazing.

    just wanted to know, when u used 260 sec exposure, then can u plz tell us which ND filter was applied. as well as kindly tell us the EXIF also.

    Thanks in advance.

  • Hi, I usually use Haida or NiSi filters, from 6 to 12 stops, depending on light conditions.

    If you want full exif, you can check my pictures on 500px or Filckr.

  • Hi Luca.

    You say that to obtain a 8 minutes pictures is like shoot 4 pictures of 2 minutes, but the information of each underexposure picture is not good, not enough.

    When light is changing, how do you know which is the correct exposure? I mean, seeing the pictures of Arco dell Pace, I would say that every picture is subexposure, even the last one. How can you obtain the information with underexposure pictures? You should change exposure in every picture, don’t you?

    And if light would not change, don’t you should exposure correctly every picture?

    Thank you very much.

  • Hi Sergio, usually when taking long exposure photos, I try to set an exposure time which allows to average the light by using natural light evolution in twilight.

    So at sunset I usually set a slightly overexposed time and keep it fixed as long as the sun is setting to get a natural “dim” of light while going on with the shooting. When shooting during sunrise, I do the opposite, I usually start with underexposed pictures and let the increasing light (thanks to the sun rising) to do the job for me to increase the exposure while going on.

    I’m not pretending this to be the best approach, but it is what I usually do to average light and color when stacking. With this technique, exposure doesn’t need to be perfect, because you average everything…

    When taking a single long exposure, I usually expose to the right, and I do this by calculating the correct exposure time with math formulas.

    You are right about the “Arco Della Pace” pictures… it was a sunrise, I was expecting the light to increase more than that, but the sun was constantly covered by the clouds, resulting in underexposed pictures. But I was able to recover details in the shadows thanks to a bracketing shot I performed without filters. 🙂

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