Glance at the summary firstThe summary from the end of the lesson, as a road map before you start reading.
Almost everything is blurry in macro, because the slice of sharpness gets four times thinner when magnification doubles and drops to roughly one millimeter at 1:1 and f/8; stopping down is limited too, because while the effective aperture is narrower than the written one, diffraction starts early. The thin slice is best used by holding the sensor parallel to the subject's most important surface and putting the focus on a priority detail such as the eye; a person's eye or skin at this closeness is photographed in its real tone, with permission, with the focus placed consciously and metered from the skin.
Learning goal
You will be able to explain why the slice that stays sharp in macro is measured only in millimeters, sometimes under a millimeter. You will know that this slice thins quickly as magnification increases, that stopping down the aperture softens the whole frame past a certain point because of diffraction, and moreover that in macro the aperture behaves narrower than what is written on paper. You will place the thin slice on the subject's most important plane, and fit more detail into the same slice by holding the camera parallel to the subject's surface. To find focus, you will slide not the lens's ring but the camera itself back and forth. When photographing a person's eye or fingertip at this closeness, you will decide consciously where the focus will fall and show the texture of light or dark skin in its real tone.
The question
With the extension tubes, your friend manages to fill the frame with the dragonfly's head and looks at the screen excitedly. The small hexagons on the front surface of the eye are razor sharp; but the surfaces a few millimeters behind soften, the back of the head and the base of the wings are a completely blurred smudge of color. Even though the aperture is at f/8, they see that the sharpness fits only into a strip the thickness of a lentil. They stop down to f/22; this time more is sharp, but everything seems to be behind a thin veil. Why is almost everything blurry in macro?
Context
In the depth of field lesson you saw that the slice of sharpness extends in front of and behind the focal plane, and how this slice changes with aperture and subject-to-background distance (Lesson 8.3). In the aperture lesson you met diffraction, light bending at the edge of a very narrow opening and softening the whole frame (Lesson 8.2). At the start of this track you also measured that the magnification ratio says what size the subject forms on the sensor (Lesson K.1).
In landscape the slice of sharpness is measured in meters, in a portrait in centimeters; in macro, in millimeters. Getting this close to the subject, everything that looks small in everyday photography turns into a huge problem: even a dragonfly's eye is deep enough to exceed the slice of sharpness. This lesson takes up why the slice of sharpness gets so thin, the limits of widening it a little, and most importantly, how to decide where to put that thin slice.
Simple explanation
Why is the slice so thin?
The thickness of the slice of sharpness changes very quickly with magnification. Roughly, when magnification doubles, the slice gets four times thinner. On a full-frame camera at 1:1 and f/8 the sharp slice is roughly one millimeter; at f/2.8 it is only around a third of a millimeter. Going to 1:2, at the same f/8 the slice approaches roughly three millimeters, and at 1:4 ten millimeters. Because the depth of a dragonfly's eye is a few millimeters, at 1:1 not even the whole eye comes out sharp.
That is why in macro, choosing the magnification is at the same time choosing how much depth will stay sharp. Instead of filling the frame exactly with the subject, shooting from a little farther, around 1:2, and then cropping often keeps more sharp. Steadying the camera is important too: in a one-millimeter slice, even breathing can shift the focus from the subject's eye to its brow.
Why isn't stopping down enough?
Effective aperture is the aperture in macro behaving narrower than what is written on paper, because the lens moves away from the sensor. Roughly, the written f-number is multiplied by one plus the magnification: a lens set to f/8 at 1:1 behaves like f/16 in terms of light and diffraction. That is why in macro diffraction starts much earlier; a lens set to f/16 behaves like f/32 at 1:1 and the whole frame falls behind a thin veil.
This sets up a tight balance between sharpness and depth in macro. In shots close to 1:1, many photographers keep the written aperture roughly between f/8 and f/11; this thickens the sharp slice a little while leaving diffraction at a bearable level. When more depth is needed, the solution isn't a narrower aperture but combining several frames focused at different depths; you will take up this method in detail in the track's last lesson.
Where do you put the slice?
Plane alignment is fitting the whole of the subject's most important surface into the thin slice of sharpness by holding the camera's sensor parallel to that surface. If you photograph a butterfly's wing not from the side but straight on, parallel to the wing surface, even a one-millimeter slice can keep the wing's whole pattern sharp. If the camera looks at the wing at an angle, the same slice cuts only a strip of the wing. On long, flat subjects, a leaf, a feather or an insect's body, this alignment is the most effective way to gain depth.
Focus priority is the decision about which detail will enter the thin slice. In a living creature this is most often the eye: if the eye is sharp the viewer accepts the softness of the rest, if the eye is soft the frame looks broken. To find focus, instead of turning the lens's ring, fixing the magnification and sliding the camera itself back and forth is more precise. With a person too, a priority is chosen: the pattern of an eye's iris, or the tips of the lashes? Around the eye, the fine lines and bluish veins of light skin, the deep creases and glints of dark skin, appear and vanish at the edge of the slice; taking the metering from the skin itself keeps the texture in its real tone.
Visual evidence
The next morning your friend photographs the same dragonfly on a reed, this time from a little farther away, around 1:2. They bring the written aperture to f/11; at 1:2 their camera uses it roughly like f/16. They hold the camera parallel to the surface facing the dragonfly's head and put the focus on the front surface of the eye.
In the frame the whole eye and the front half of the head are sharp, the base of the wings softens. In another frame they turn the camera parallel to the wing: the wing's whole net is sharp, the eye soft. They see that the two frames are two different priorities.
Their sister, with warm olive-brown skin and dark brown eyes, gives permission for her eye to be photographed up close. Your friend holds the camera parallel to her eye and puts the focus on the pattern of the iris; the tips of the lashes stay soft. In window light, the dark brown rings of her iris, the fine creases of the lower lid and the warm tone of her skin are detailed.
Common mistakes
Common mistakeStopping the aperture down to f/22 for depth.
In macro the effective aperture becomes much narrower and diffraction softens the whole frame. The fix: keep the written aperture roughly between f/8 and f/11.
Common mistakeHolding the camera at an angle to the subject.
The thin slice cuts only a strip of the surface. The fix: hold the sensor parallel to the subject's most important surface.
Common mistakeLooking for focus with the lens's ring.
The magnification changes too and the slice slips. The fix: fix the magnification, slide the camera back and forth and put the focus on the eye.
Summary
Almost everything is blurry in macro, because the slice of sharpness gets four times thinner when magnification doubles and drops to roughly one millimeter at 1:1 and f/8; stopping down is limited too, because while the effective aperture is narrower than the written one, diffraction starts early. The thin slice is best used by holding the sensor parallel to the subject's most important surface and putting the focus on a priority detail such as the eye; a person's eye or skin at this closeness is photographed in its real tone, with permission, with the focus placed consciously and metered from the skin.
Mini assignment
In this assignment you will measure and place the slice of sharpness in macro.
- Put a ruler on the table, standing at forty-five degrees to the camera, and with a macro lens or extension tube, at a ratio close to 1:1, shoot at f/2.8, f/8 and f/16; in each frame read how many millimeters stay sharp.
- Photograph a leaf or a feather first at an angle, then parallel to its surface, and compare the area that stays sharp.
- Photograph a living creature, or ask permission from someone close to you to photograph their eye; put the focus first on the eye, then on another detail, and look at how each priority changes the frame.
Check yourself
- At which aperture was the sharp slice thickest, and at which did the frame start to soften?
- How much did the sharp area grow when you held it parallel?
- Are the details of the eye or the skin sharp and in their real tone?
Glossary
| Term | Short definition |
|---|---|
| Effective aperture | The aperture in macro behaving narrower than written because the lens moves away from the sensor; roughly the f-number multiplied by one plus the magnification. |
| Plane alignment | Fitting the whole of the subject's most important surface into the thin slice of sharpness by holding the sensor parallel to that surface. |
| Focus priority | The decision about which detail, most often the eye, will enter the thin slice of sharpness. |
Mini quiz
1. In macro, what happens to the slice of sharpness when magnification doubles?
- A) It gets twice as thick
- B) It gets roughly four times thinner
- C) It doesn't change
- D) It gets half again thicker
2. At 1:1, roughly what effective aperture does a lens set to f/8 work at?
- A) f/4
- B) f/8
- C) f/32
- D) f/16
3. What is the most effective way to keep a butterfly's whole wing sharp?
- A) Holding the sensor parallel to the wing surface
- B) Stopping the aperture down to f/32
- C) Looking at the wing at an angle
- D) Relying on autofocus
4. Which is the most precise way to find focus in macro?
- A) Turning the lens's ring quickly
- B) Shaking the camera in the hand
- C) Fixing the magnification and sliding the camera back and forth
- D) Opening and closing the aperture
Answers
- B — The slice of sharpness thins with the square of magnification; twice the magnification gives a slice four times thinner.
- D — The effective aperture is the written f-number multiplied by one plus the magnification; eight times two makes sixteen.
- A — A surface standing parallel fits into the thin slice from end to end.
- C — The ring changes the magnification too; sliding the camera moves only the plane of focus.
Summary card
- Magnification twice, slice four times thinner; at 1:1 and f/8, roughly one millimeter.
- The effective aperture is narrower than written; diffraction starts early in macro.
- Keep the written aperture roughly at f/8–f/11; for more, combine several frames.
- Hold the sensor parallel to the important surface; put the focus on the eye.
- Focus by sliding the camera; for a person's eye, ask first, read the light from the skin.
Bridge to the next lesson
The dragonfly's eye is sharp now, but at f/11 and 1:2, in the morning shade, the shutter speed drops to 1/15; the frame on the reed swaying in the wind shakes. When they raise the ISO, grain settles over the frame. And when they get closer to add light, their own shadow falls on the dragonfly. How do you light a small world? The next lesson takes up the ring flash, diffusers fitted to the front of a small flash and reflectors in macro.