In macro photography there is another force at work when it comes to aperture selection and the resulting depth of field, writes Andrew James & Jon Adams. In our aperture related article from a couple of weeks ago – Aperture Choice – we looked at what aperture actually is and how understanding what it does makes a huge difference to your creative photography. In this related article, we are going to look specifically at aperture and what you need to think about when you are using a macro lens.
Magnification and sharpness
AJ Says: While the principles of the f-stop sequence (f/2.8, f/4, f/5.6, f/8 and so on) and how each full stop either doubles or halves the amount of light reaching the camera’s sensor remains the same, there is a significant difference in the amount of sharpness you get when using a macro lens. Why? Well, the issue all stems from the whole purpose of macro photography – its ability to photograph something small, such an insect or water droplet, at life size or possibly magnified so it is even larger than life size.
Aperture (the f-stop you have chosen) has the function of controlling light. As we open up or close down the aperture there is also the reciprocal effect that governs how much sharpness we have in an image. For example, taking the extreme ends, f/2.8 (a wide aperture) has very little sharpness behind and in front of the point of focus, while f/16 has much greater through the image sharpness. In macro photography this working principle is the same – except the amount of sharpness you get is much less that it would be with a non-macro lens. This is because this through-the-image sharpness that we know as depth of field, is governed by the aperture selected and the magnification. At any aperture, the more the magnification, the less depth of field.
Imagine you want to photograph something really small, so small in fact that to have it fill the frame you would have to use a ratio of 4:1. Now a standard macro can’t go beyond life size (1:1) but you can when using certain accessories or perhaps a specialist lens, such as the Canon MP-E 65mm that allows you to magnify up to 5x life size. When you photograph your subject at 4:1 ratio, even at an aperture of f/16, then depth of field will be measured in a few millimetres, even though the same f-number used on a wide angle for a landscape photo can render good sharpness from the foreground to something in the distance that’s a good walk away! It’s all down to that magnification. Greater magnification equals dramatically reduced depth of field.
Most of you will be working with a standard 1:1 macro, although some may have a macro setting on a telephoto lens. The macro setting on a telephoto is NOT true macro. Check out our article – Choosing a Macro Lens – for more info on this. While depth of field is limited even at the smaller apertures, it doesn’t mean you shouldn’t be using them. To maximise sharpness stick with the same basic principles that you would when shooting with any lens…
Different macro ‘camps’
JA says: When it comes to choosing a subject, macro falls – very broadly – into two camps: ‘tabletop’ – where you have full control over the situation in a still-life sense; and ‘nature’ – where you’re likely outdoors and are dealing with variables that are out of your hands. Because smaller apertures are needed if you want a modicum of depth-of-field in your shots, you need to get lots of light into the camera. For tabletop, you can do this with longer exposures, so provided the camera’s on a tripod and the subject can’t move, then using aperture priority, setting a small aperture of f/16 or f/22 and allowing the shutter speed to extend to whatever it needs to be, you’re all set for great shots. Any extra light you use is for modelling purposes rather than raw illumination, so torches, LED lamps or small reflectors can all come into play to make your small-scale stage look good. Whether you’re shooting the tips of pencils, the delicate curves of paper curls or the interaction between oil and water in a glass tumbler, a small Maglite or two will work wonders on creating a great looking scene.
Go into the realm of nature though, and the game changes dramatically. Instead of the proactive world of tabletop shooting, where you’re setting up and controlling everything, you’re dealing with a more reactive style, as you have to respond to a flower head bobbing in the breeze or a damselfly buzzing around. The leisurely route of longer exposures is no longer an option when your subject is moving, so the extra light you need to satisfy those smaller apertures has to come from somewhere else. On a bright sunny day, you might have just about enough to maintain a fast-enough shutter speed to freeze an insect in flight, but this will often mean cranking up your ISO to a higher value like 1600 to make the chip more sensitive to light. And once the sun ducks behind a cloud – assuming it was out at all – then you’re a bit stuck unless you can fire enough extra light into the scene to freeze the subject’s motion. Nine times out of ten, this means using flash, and flash is so important to macro in the field, that there’s a whole host of dedicated guns to make it possible.
You can’t use a pop-up flash or a regular hotshoe mounted unit, as the angles are wrong, and the lens itself will cast a shadow over the subject. In the main, the choices are off-camera flash – ideally on some sort of bracket to keep things mobile and quick to use, or a dedicated macro ring flash that mounts on the end of the lens and gives stacks of light because it’s so close to your subject.
AJ says: However you work with the depth of field limitations of macro, there is still that burning question, what aperture do I use? As is often the case in photography there is no definitive answer and actually, just assuming that you use a small aperture to maximise sharpness isn’t the only answer because even if you do, you may not get the sharpness you really want. Also, if you do get the sharpness at, say f/11, f/16 or f/22, it can be at the expense of other things, such as a non-distracting background.
You certainly don’t want to stampede to the smallest aperture available on your macro lens either. This is typically f/32. At this aperture you may suffer from image quality issues that negate the point of using it for added depth of field. Again, to understand why check out our article – Aperture Choice. For me – and I am deliberately avoiding the technique of focus stacking here – it is the aesthetic of the image that is the most critical thing, but I have to be aware when shooting what the limitations of sharpness will be and how to work around them.
For example, I really like this shot of a speckled bush-cricket, even though it’s not sharp throughout the insect’s body, it’s sharp where it needs to be. It was taken at f/8 and the focus, as you can see from the second image when you scroll, is on the root of the antenna. Its eyes are sharp but some of the body, the antenna and legs and falling out of focus. A smaller aperture – f/22 for example – would have provided more in the body but it would also have made the background more cluttered (it’s borderline anyway). At f/8 I think I had the best compromise between sharpness and diffusion in the background. The only way I could have got it sharper was to focus stack but that would rely on her sticking about and not moving. I can tell you she hopped off shortly after I took the shot.
This butterfly shot has been taken at f/5.6 which obviously gives less depth of field than the cricket image. But the butterfly is sharp. It’s simply down to positioning and making sure the lens is exactly parallel to the insect’s body so the plane of focus is right across the body and wing. At f/5.6 the background grass has diffused enough to allow the butterfly to stand out really clearly. Essentially you need to think about the position of the subject to the lens and whether absolute sharpness is a prerequisite of a successful image. Unless it’s a scientific identification shot, I’d suggest that very often you can play around with depth of field and very much use it for creative effect.
Finally, this butterfly photographed during lockdown this summer was deliberately taken with a very limited depth of field by using f/4 and focusing on the front of its head. The wings and legs are all out focus but the shallow depth of field is pleasing.
Good working practises for macro
JA says: Whether you’ve gone for the ‘nature’ or the ‘tabletop’ approach, once you’ve decided on your subject and have enough light present, there are a few standard practices that will ensure great results. The first is to make an assessment of how your chosen aperture will look in terms of the depth of field in the shot.
To make this assessment, you have three options. The Depth of Field preview button on your camera is the traditional choice, as this will close down the aperture to whatever value you’ve set and show you in the viewfinder which areas will be rendered sharp. While effective, it does give a darkened viewfinder image, so if you’re using a small aperture like f/16 or f/22, it may be difficult to see what’s going on – especially on a sunny day if your eyes have adjusted to the bright conditions.
With film cameras in the days of old, this was a problem, but with the instant feedback from a screen on the back, you can just take a quick test shot to check how it’s going to look. In fact, taking and reviewing a test shot takes about the same time as pressing a DoF preview button and squinting through the ‘finder, so these days, many photographers will prefer the DoF test shot to the DoF preview!
Another option is using LiveView to compose and evaluate your shot, as when the shutter button is half-pressed, this will show you a WYSIWIG image, and will let you see the impact of the f-stop you’ve selected. LiveView is also a smart option for the hyper-critical focusing that macro requires. By engaging LiveView and hitting the Zoom in button, you can magnify your point of focus on screen and make sure it’s spot on – tweaking the focus ring in Manual Focus mode. This is the best way to work in a tabletop scenario when you’re on a tripod and have full control, though is pointless if you’re handholding and trying to chase a bee round a flower!
In situations where you need more DoF than is possible – even at your smallest aperture, then focus stacking is a common solution. This is a procedure where several shots are taken at slightly different focusing distances, and then the sharp parts of each are seamlessly blended together to give an extended depth of field. Scroll between the two images below and you’ll see the difference it can make. The unstacked image is shot at f/8, while the stacked image is a blend of 20 images all shot at f/8!
Some more advanced cameras offer in-camera focus stacking, but for most, it combines a delicate manual focusing technique at the shooting stage with either manual or automated post-processing in imaging software. We don’t have room to cover focus-stacking in detail here, but keep an eye out for an article on this rewarding technique in the coming months.