Stacking in Photography - What is it and Why Bother?

I use stacking a lot in my photography and I mention this when I have posted images to social media and hence one of the questions I get asked most is; what is stacking? So that is what I’m going to write about.

Edit - I have since writing this blog done a huge course with the brilliant School of Photography all on Macro Photography if you want to know more details go HERE

So what is stacking?

Quite a Complicated Scene Set

Stacking is simply a technique used in photography where you take multiple photographs and merge them. One of the main reasons to do this increase how much of the image is in focus. The amount of a photograph that is in focus is called the ‘depth of field’. The next section is going to be a  little bit technical but I think it helps to understand stacking.

There are a number of things which impact the depth of field;

1. The focal length of the lens - If you use a wide-angle lens you get a much bigger depth of field than if you use a long telephoto lens (all over things being equal). For example, when you use a wide-angle lens ie 18mm for landscape photography it’s easy (most of the time) to get everything in focus and when you use a long lens to photograph birds it’s easy to get a shallow depth of field and only the bird is in focus.

2. The aperture used has an impact on the depth of field - The aperture is basically the opening in the lens in which light passes through. Basically the wider the aperture (which is defined by a small number eg f/2.8) the more light comes into the camera and also the depth of field is smaller ie less of the image is in focus. If you use a narrow aperture (defined by a big number eg f/14) less light comes in and the depth of field is larger ie more of the image is in focus.

3. How close you are to the subject that you are focusing on - This is the big one! The closer you are to the subject that you are focusing on the shallower the depth of field. This isn’t even a liner relationship as you closer to the subject the depth of field reduces exponentially.

Some examples which may bring the above to more life. If I’m doing aurora photography I’m using a wide-angle lens often a 14mm so that automatically gives me a large depth of field (I’m going to call it DOF now as I’m typing it too often!). I’ll be using a very wide aperture usually about f/2 which should mean I get a shallow DOF but because I focusing on the stars (ie something very far away) I have a huge DOF. 

Basically put those numbers into a DOF calculator and everything in front of the camera after 3.2 meters away to the stars would be in focus (in the above example, on the above settings the tree is more than 3.3 meters away so everything from the tree to the stars is in focus). So the DOF would be in effect infinite. Now if I kept everything the same, apart from where I focused and I changed it so I was focusing on something that was only 1 meter away. Then in front of my camera, the only bits that would be in focus would anything which was further away than 77cm and nearer than 143cm. Therefore my depth of field would be 66cm. Obviously that is a huge difference from infinity!

Now when you take this to macro photography the DOF gets way smaller. In macro you tend to use much longer lenses and you are much closer to the subject.

So for example, if I use my Canon 5D4 and a 100mm macro lens set the aperture to f/5.6 and focus on something at 35 cm from the camera sensor by DOF is only about 1mm! 

If I swap lenses and use my Canon MP-E 65mm and then put it to five times magnification this even further reduces the DOF to a staggering small 0.095mm!!!

So that was the end of the technical stuff but there was a point to it! 

Now when we look at a scene with our eyes, our eyes are like two fantastic quality lenses. Our eyes sample the scene in front of us at various focus points and then our brain takes all of the information and produces the image ie what we see. You can test this easily by closing one eye and seeing the DOF in your view decrease, especially if you try focusing on something close to your eyes. If you looked at a large macro subject which is easy to see, say like a dragonfly and then you took a single photo of the dragonfly and compared the two. You would easily see that the DOF you can see with your eyes is much greater than that you can get with a single image. 

Why have I gone this long route of explanation? It’s to try and say why I stack my images and that is to try and get a similar DOF that I can see with my eyes! As now hopefully you understand when you are doing a macro image the DOF is so small you can only get a tiny element of the image in focus when I look at the dragonfly covered in dew with my eyes at the side of the pond I can see it all in focus in my head and I want my images to look more like that.

So what is Stacking (again)?

In simple terms, stacking is when multiple photographs have been taken of the same subject where the focal plane (ie the part of the photograph that is in focus) has changed. This can be any number of photographs from 2 onwards. It just depends on how much of the image you need or want to be in focus. Those photographs are then merged in software. The software will then take all of the bits which are most in focus and merge then into one image. Therefore the final output, if everything has worked, will be an image with a bigger DOF.

Have a flick through the below gallery. Each of these is a single photo of dragonfly covered in dew. On each photo only a fraction of the dragonfly is in focus but as you flick through the individual images you can see the bits of the dragonfly which is in focus changes.

Then in this next version, all of the above images have been merging by stacking, in this example using Photoshop. This creates a dragonfly where the entire image is in focus with all the essential bits of the image being sharp.

How do you Physically do it?

I’m not going into a lot of detail here otherwise this is going to be too long a blog (I will cover them in some more blogs later though). But in short, there are a number of methods;

Move the camera towards the subject this can be done using a tripod and a macro rail or in the case of active critters can be done handheld. As you move closer to the subject the focal plane moves in proportion to the camera moving.

Watch the below video which demonstartes me using this technique to photograph jumpings spiders.

Move the focus ring take a picture, rinse and repeat. Each time you move the focus ring again you move the focal plane. It’s important to note though, this will also increase the magnification of the image too. Which can be corrected in the post-production but does need to be corrected.

Some cameras now offer in-camera focus bracketing. This will only work with lenses that have an automatic focus system. I have not used this much yet.

Is this Cheating?

I do get asked this quite often. In my eyes, most major competitions and publications it is not. It’s an accepted photographic technique. You are not creating something that is not there. But as ever photography is quite subjective and if you think it is cheating, fair enough.

What are the benefits?

To me they are numerous but some of these again are subjective, often in photography, there are no right or wrong answers. It’s just understanding that there is a difference and when it’s good to use one technique and when to use another.

The two key benefits to me;

1. It allows me to isolate the subject and get incredible detail at the same time. Often my subjects are found in messy environments for example dragonflies. They will be among grasses or reeds and if I use the aperture eg f/14 to get a larger DOF the background will become very obvious and distracting. Whilst if I use a wide aperture I have a shallow DOF and therefore the background becomes a lovely blur.

Some examples would be;

When I first started doing macro photography I used to use flash nearly all of the time like probably 95% of macro photographers do. But flash comes with its own issues such as flash highlights overexposing, flash drop-offs, impact on colour, impacts reflections/refractions etc if I stack I can use a wider aperture to let more light into the camera and therefore work with natural light more.

For example;

What are the downsides?

• It takes more effort. As you are taking more pictures to get one image there’s extra work both in the field and when you get home.
• With high-resolution files the actual computer work can take some time and you need a powerful Mac or PC to be able to do it.
• It can actually be quite tricky to get it to work. Especially small subjects that move when you have to go handheld. So it takes a lot of practice.

Is it limited to macro photography?

Absolutely not. I have used it many different genres of photography. Including landscape, wildlife, aurora and architecture photography.

Here are a few examples;   

So I hoped that explains what stacking is and why I use it often.  Not just in macro photography either. It makes many more image types possible.

I will do some more blogs in the near future about how you actually do the stacking too and the different types of stacking.

I hope that was of use and feel free to leave a comment or share the blow with anyone who may be interested.

All the best,

Oliver