Focus-stacking is a technique photographers use when they can’t get all of their subject in focus in a single shot. And it’s a technique that I use almost all the time for my artefact photography.
But, what do I mean by getting all your focus in one shot?
I think everyone’s familiar with the idea of focus being about getting a sharp, not blurry, image.
However, various factors can affect how much of your photo is sharp.
This ‘amount’ of sharpness is called ‘depth-of-field’, and it’s usually referred to as being either shallow or deep:
Shallow depth-of-field Not very much of the photo’s in focus. Think of portraits of people, where their face is in focus, but the background is pleasantly blurry.
Deep depth-of-field All (or most) of the photo’s in focus. Think of landscape photos, where everything from that big rock in the foreground to the hills on the horizon are sharp.
To a certain extent, photographers can control this depth of field in two ways:
- You can use your aperture (f/stop) on your lens. Narrow apertures create a deeper depth-of-field than wide apertures
- You can use different lenses/zoom. Wide-angle lenses have a naturally deeper depth-of-field that longer (zoomed-in) lenses
However, this sometimes isn’t enough to get your whole photo in focus. My macro lens, for instance, is a longer lens – it’s not a wide-angle – so no matter how narrow my aperture (for those interested, its maximum is f/22), I’m not always going to get all my photo in focus.
So instead, I use focus stacking to pick up the slack.
To try to put the process in a nutshell, when you focus-stack, you take multiple photos of your subject, moving the focus a little each time. You then create a composite image on the computer, using the sharpest parts from each photo in the stack.
(FYI, if you use a mobile phone for photography, phones usually have wide-angle lenses which will create a deep depth-of-field. Some phones can now create a shallow depth-of-field for you on photos of people. This, however, hasn’t been created using different settings or lenses; the camera uses facial recognition to blur the background for you after the photo’s been taken.)
What's the process for doing focus stacking?
When I do focus stacking, it’s quite a carefully controlled process.
I’ll talk you through the steps using the image I created of a Predynastic pot for the Before Egypt exhibition.
It’s a marvellous pot; it’s ceramic, but decorated with splats of red paint to mimic the texture of stone. We’ve nicknamed it ‘Splatty Pot’. Naturally …
Anyway, back to the job in-hand. I have my camera on a tripod and all the settings are done manually. I don’t have anything on auto, to keep everything consistent across the stack of images. The only variant is the focus, which is done manually, too. I can’t have the camera making any decisions for me. Differences between the photos will make things harder for me later down the line.
I use a setting on my camera’s manual focus called ‘focus-peak highlighting’. This puts little blue highlights on my viewfinder to show me which part of the photo’s in focus. Being able to see exactly which part of the photo’s focussed makes my life a whole load easier.
Not only can I see where the camera’s focussed, I can make my adjustments to the focus very precisely, very quickly.
This photo shows the back of my camera whilst doing a focus-stack. The blue dotting on the camera screen’s showing me what part of the image is in focus. You can see that very little of this pot’s actually in focus (more on why that is below).
I then take a series (stack) of photos, moving the focus a little each time, from front to back. Everything else about the photo is identical.
Splatty Pot needed fifty photos in total to get everything in focus.
This is the first image in the stack. You can see that the pot’s in focus at the front (bottom left corner of the image), but it drops off again as you move backwards.
This is the last photo of the stack. Only the very back part of the pot (top right corner of the photo) is in focus.
Once this is done, I load the stack of photos into software on my computer.
You can use Photoshop, but it’s clunky and slow and annoying. It’s one of the few things that Photoshop’s not actually very good for.
Instead, I use a piece of software called Helicon Focus, who’s main life goal is to focus stack. (It’ll do in ten minutes what Photoshop takes two hours to do.)
Once the stack of images is loaded, Helicon Focus takes the sharpest part of each photo and creates a composite image, which I then save out as a TIFF and edit in Photoshop.
This is the part of the process that needs the consistency across the photos. If the exposure or light balance is different in some of the photos, Helicon Focus will struggle.
It also needs to have the focus moving in one direction from the first to the last photo. If the focus jumps backwards and forwards rather than in a straight line, Helicon Focus will throw a hissy fit, tell me off and go on strike.
Consistency is key!
This is a screenshot of Helicon Focus. On the left is the photo currently being processed. To its right, the funny fuzzy part is the composite image being built up.
On the far right of the screen is the stack of photos (you can check and uncheck images to include or exclude them from the composite), as well as the various options for creating the composite image.
And here’s the finished image. Sharp from front to back!
Why do I use focus-stacking?
Apart from the blindingly obvious thing of getting-everything-in-focus, there’s one huge reason I do a lot of focus-stacking: the closer you are to the object you’re photographing, the shallower your depth-of-field.
Without going into too much physics, when you get closer to something, focus falls away again more quickly than when you’re further away. And I do a lot of close-up work.
So, while you can go out and take a photo of a landscape, getting miles of sky and hills and sea in focus in a single shot, when you get your macro lens right up in the face of a tiny amulet, your depth-of-field lasts mere millimetres.
This means that a lot of the time, I have no choice but to focus stack, as shown by Horus below:
This image on the left’s the first image in the stack. You can see that just Horus’s beak is in focus.
This image on the right’s the final image in the stack. You can see that just Horus’s back arm is in focus.
And here’s Horus in all his focus-stacked glory!
(65 images, in case you were wondering.)
The advantages of focus-stacking
I focus-stack most of the photos I take of objects. When I’m showing artefacts – some of them very tiny – I want to capture details in shape, texture and form, so I need to know I’ve got everything I’m going to want to show.
Even the bigger pots that I photograph from further away get stacked. It may be only four or five photos in the stack, but I know I’ve got a really sharp image.
Using Helicon Focus then gives me even more choice. Once I’ve got my stack of photos home, I can create an image that’s sharp all the way through, or I can go back and use fewer photos to create an image with selective focus.
When I’m under pressure to get objects photographed, and I’ve already had to think about lighting and composition, being able to think about depth-of-field at a later date makes my workflow more efficient.
In these two images, I didn’t want sharp focus throughout. I’ve used more selective focus to draw your eye to the most important part of the photo: the spots on the rim of the red pot (left) and the detail in the lug handle (below).
The disadvantages of focus-stacking
As is the way with life, there are disadvantages to consider with focus-stacking:
- You’re taking more photos, so you need more storage. I might come home from a session at the Garstang with 500 photos instead of twenty or so. This means the number of external hard-drives hooked up to my PC is ever increasing
- You need to know how to use manual settings on your camera – shutter speed, aperture, ISO, white balance and focus
- You need extra software, such as Photoshop or Helicon Focus, to process your images
- You need extra hardware, such as a tripod, to keep your camera in the same position for each photo you take
- It’s tricky to do focus-stacking on the fly, such as in a museum gallery, because you need to keep everything but the focus as near to identical in each photo as you can. And museums generally don’t like it if you start whipping out your tripod and moving other visitors out of your way in the middle of their galleries …
- Stacks with a lot of images take longer to photograph. Not vast amounts of time, but if you’re photographing several objects, the process can start eating into your day
But, when all’s said and done, the benefits definitely outweigh the downsides, for sure. For me, it’s an integral part of my workflow, and I certainly couldn’t do the amulet photography without it. The only ongoing expense is the extra hard-drive space I need to store all the photos. But, these days, external drives really are quite affordable.
I hope that’s given you a bit of an insight into how I work. And, for those of you who might want/need to pursue museum photography, it’ll give you an idea of some of the skills you might need in the future.
If you have any questions about focus-stacking, or how I do my photography, please do ask in the comments below.
This wasn’t meant to be a tutorial. It’s just a demonstration of some of the work I do. However, if you’re interested in learning the technique, I’m looking at putting a workshop together. Please sign up to my mailing list below if you want to keep up-to-date.
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