Canon VCM and Focus Breathing Control

Focus Breathing Explained: How VCM Technology May Help Control It

Focus breathing can subtly change framing as focus shifts. Explore the phenomenon and how Canon VCM technology may help control focusing behaviour.

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Vernon Chalmers Photography approaches focus breathing from both a practical photography and technical-training perspective. The phenomenon is considered in the context of modern Canon mirrorless cameras, autofocus systems, wildlife and Birds in Flight photography, and the increasing integration of optical, mechanical and electronic lens technologies. The discussion distinguishes the optical causes of focus breathing from the role of VCM focusing actuators, avoiding the assumption that VCM itself automatically eliminates the phenomenon.

How Canon VCM and Focus Breathing Work

• Dual Motor Design: A powerful Voice Coil Motor (VCM) moves the larger main focusing group, while a smaller Nano USM simultaneously adjusts a separate electronic floating lens group.
• Independent Group Movement: Because the two groups move together or independently, the lens corrects optical variations in real time.
• Optical Suppression: This floating design keeps the size of background elements constant when you change focus, largely removing the need for heavy digital crop correction.
• Extra Digital Correction: You can combine the lens's built-in optical control with in-camera Focus Breathing Correction on supported EOS R bodies for a completely locked frame.
• Power Requirement: VCM actuators need camera power to hold lens groups in place, meaning internal components might gently shift or click when the camera is switched off.

Focus Breathing and the Future of VCM Autofocus

Photography often encourages us to think of focusing as a simple binary process: the camera focuses, the subject becomes sharp, and the photograph is made.

Optically, however, something more interesting can happen.

As a lens changes focus from one subject distance to another, its apparent angle of view can also change. The subject may appear to become slightly larger or smaller within the frame, even though the camera itself has not moved and the photographer has not deliberately changed the focal length.

This phenomenon is known as focus breathing.

For many still photographers, focus breathing is barely noticeable and has little practical consequence. For photographers working with video, macro photography, wildlife, birds in flight and increasingly sophisticated autofocus systems, however, it can become much more significant.

The emergence of technologies such as Canon's VCM — Voice Coil Motor — focusing systems makes the subject particularly interesting. VCM does not, by itself, eliminate focus breathing. Focus breathing is fundamentally an optical and mechanical characteristic of a lens. But increasingly sophisticated focusing mechanisms can provide the precision and responsiveness needed to control focusing groups more accurately.

This places focus breathing at an interesting intersection between optical design, autofocus technology and creative vision.

What Is Focus Breathing?

Focus breathing describes a change in the apparent framing or angle of view of a lens as the focus distance changes.

Imagine placing a camera on a tripod and photographing a subject some distance away. Without moving the camera, you focus on that distant subject. You then focus on a much closer subject.

The image may appear to change scale.

The closer subject may appear to become larger, or the overall field of view may appear to narrow or widen. The effect can sometimes resemble a small change in focal length even though the photographer has not changed the lens's stated focal-length setting.

The camera has remained stationary.

The lens has not necessarily been zoomed.

The composition has nevertheless changed.

That is focus breathing.

The effect varies enormously between lenses. Some designs exhibit very little breathing, while others can show a much more obvious change in framing.

This is one reason why the focal length printed on a lens should not be interpreted as describing every aspect of its optical behaviour at every focusing distance.

Why Does Focus Breathing Occur?

The explanation lies in the optical geometry of focusing.

A photographic lens does not simply move the entire optical assembly backwards and forwards every time it focuses. Modern lenses frequently use internal focusing, in which one or more groups of optical elements move relative to the others.

Changing the position of these optical groups changes the way light travels through the lens.

The result is a change in the optical characteristics of the system as the focus distance changes.

One consequence can be a change in the lens's effective field of view.

This is why focus breathing is fundamentally different from conventional optical zooming.

With a zoom lens, the photographer deliberately changes focal length.

With focus breathing, the apparent change in framing occurs as a consequence of changing focus.

This distinction becomes particularly important when observing a lens during a focus transition.

The Simple Photographic Example

Consider a 100mm lens focused on a distant subject.

The photographer then changes focus to a subject considerably closer to the camera.

If the lens exhibits noticeable focus breathing, the second frame may show the subject at a subtly different scale.

The photographer has not moved.

The zoom ring has not moved.

Yet the composition has changed.

In a still photograph this may be almost impossible to notice unless the two images are compared directly.

During video, however, the effect can become obvious.

A deliberate focus transition from one subject to another can produce an unintended visual impression that the camera is simultaneously zooming.

This is why focus breathing has traditionally been an important consideration in cinematography.

Focus Breathing and Video

The phenomenon becomes particularly obvious when a photographer or cinematographer performs a focus pull.

A focus pull deliberately changes focus from one subject or plane to another.

For example, a scene might begin with a foreground object sharply focused before the focus transitions smoothly to a person in the background.

Ideally, the viewer should perceive a change in focus.

The framing should remain essentially stable.

A lens with significant focus breathing can introduce another visual event: the apparent field of view changes during the transition.

The viewer may therefore perceive both a focus change and a subtle zoom.

For conventional still photography this may be irrelevant.

For video it can become an important characteristic of the lens.

Why Focus Breathing Matters to Photographers

The importance of focus breathing depends heavily upon the photographic discipline.

For general still photography, it is often a minor consideration.

A photographer focuses, captures the image and moves on.

There is no extended period during which the viewer watches the lens transition between different focus distances.

There are nevertheless circumstances in which it can matter.

Macro and Close-Up Photography

Focus breathing can become more apparent in close-up photography because focusing distances change substantially relative to the subject.

A photographer working close to a flower, insect or small object may notice changes in subject magnification as focus is adjusted.

This becomes particularly relevant when focus stacking is involved.

A sequence of images captured at different focus distances ideally maintains a consistent composition. Changes in framing between frames can complicate the subsequent stacking process.

Wildlife Photography

Wildlife photography introduces another interesting consideration.

A bird may move toward or away from the photographer while the autofocus system continuously adjusts focus.

The lens is therefore constantly changing its focusing distance.

If the lens exhibits significant focus breathing, the apparent framing can change as autofocus tracks the subject.

For a single still frame this may be insignificant.

For a sequence of images, however, the effect can become more noticeable.

Birds in Flight

Birds in Flight photography provides an especially useful real-world example.

A bird approaching the camera can require substantial changes in focus distance. The autofocus system may move focusing elements rapidly to maintain subject acquisition.

The photographer is attempting to maintain a stable composition while the subject itself is moving unpredictably.

Here the photographer's intention is essentially:

Track the subject, maintain focus and preserve the composition.

Focus breathing introduces another variable.

The effect is generally much less important than autofocus acquisition, tracking performance, shutter speed, subject movement and technique. Nevertheless, it illustrates how optical behaviour and autofocus behaviour are increasingly interconnected.

Canon VCM: The Future of Autofocus

The VCM Connection

This brings us to Voice Coil Motor technology.

VCM is an electromagnetic actuator used to move focusing elements within a lens.

Unlike a conventional mechanical focusing system that relies upon a more traditional motor-and-gear arrangement, a voice coil motor can provide highly responsive movement of an optical group.

The significance is not simply that the lens can focus quickly.

It is that the focusing mechanism can be controlled with considerable precision.

This distinction matters.

Focus breathing is not caused by a motor being slow.

It is caused primarily by the optical design and the movement of focusing groups.

Consequently, it would be technically incorrect to state:

VCM eliminates focus breathing.

It does not.

Instead, VCM can form part of a more sophisticated optical and focusing architecture in which the movement of individual focusing groups can be controlled extremely precisely.

VCM Is an Enabler, Not the Cure

This is an important distinction when discussing modern lens technology.

A VCM actuator moves an optical group.

The optical design determines what happens when that group moves.

Therefore, reducing focus breathing depends upon the interaction of several factors:

• the optical formula of the lens;
• the number and configuration of focusing groups;
• how those groups move;
• the relationship between focusing distance and effective focal length;
• the electronic control of the focusing mechanism;
• and the software and firmware controlling autofocus behaviour.

VCM provides the actuator.

The optical engineers determine what the actuator is being asked to do.

This is why the relationship between VCM and focus breathing should be understood as enabling greater control, rather than automatically eliminating the phenomenon.

Independent Focusing Groups

One of the most interesting developments in modern lens design is the ability to control different focusing groups independently.

This allows the optical system to perform more sophisticated corrections as the focus distance changes.

Instead of treating focusing as the movement of one simple optical block, the lens can use coordinated movement of multiple groups.

This creates additional opportunities for optical designers.

The focusing system can be designed not merely to achieve focus, but to achieve focus while maintaining other desirable optical characteristics.

That can include maintaining a more consistent field of view throughout a focus transition.

This is where advanced focusing actuators such as VCM become particularly relevant.

From Autofocus Speed to Optical Control

The evolution of autofocus technology is therefore interesting because the objective is changing.

Earlier generations of autofocus systems were often judged primarily by how quickly they could acquire focus.

Modern mirrorless systems have considerably expanded the definition of autofocus performance.

We now routinely consider:

• subject detection;
• eye detection;
• tracking;
• predictive focusing;
• continuous Servo AF;
• focus acquisition;
• focus stability;
• transition behaviour;
• and communication between camera and lens.

The lens is no longer simply a passive optical device attached to the camera.

It has become an electronically controlled optical system.

VCM technology is part of this broader transition.

Focus Breathing and Creative Vision

This is where the phenomenon becomes particularly relevant to the Creative Vision concept.

A photographer normally thinks of focus as determining what is sharp.

Focus breathing reminds us that focusing can also influence what the lens sees.

That is a subtle but important distinction.

The act of focusing is not necessarily optically neutral.

When the focusing groups move, the optical geometry of the lens can change.

The photographer may therefore be changing more than the plane of focus.

The image itself can undergo a small change in perspective-like framing.

This is one of those characteristics of photography that is usually invisible until we deliberately look for it.

And once we see it, we begin to understand lenses differently.

The Future Significance of VCM

VCM technology is therefore interesting not simply because it can make autofocus faster.

Its greater significance may lie in the increasing precision with which optical systems can be controlled.

As Canon and other manufacturers develop increasingly sophisticated mirrorless lenses, the distinction between optical design, autofocus mechanics and computational control becomes less obvious.

The focusing system can increasingly be regarded as an integrated system.

The camera determines what needs to be focused.

The autofocus algorithms determine how that focus should be achieved.

The lens receives those instructions.

The focusing motor moves the optical groups.

The optical design determines the resulting image.

VCM sits within this chain as a highly responsive means of moving the focusing elements.

That makes it potentially valuable in managing optical behaviour during focus transitions.

What This Means for the Photographer

For photographers, the practical lesson is relatively simple.

Focus breathing is not necessarily a defect.

It is an optical characteristic.

A lens that exhibits some focus breathing may still be an exceptionally capable photographic lens.

For many still photographers, the phenomenon may never be noticeable in normal use.

For photographers working in video, macro, focus stacking or demanding subject-tracking situations, however, it becomes more relevant.

The increasing sophistication of mirrorless autofocus means that photographers are also becoming more aware of what happens during the focusing process itself.

This changes how we evaluate lenses.

The question is no longer simply:

How sharp is the lens?

It can also become:

How does the lens behave while it is focusing?

That is a much more sophisticated question.

Focus Breathing as Part of Lens Character

Every lens is a collection of compromises.

Optical designers balance resolution, contrast, aberration correction, size, weight, maximum aperture, focusing distance, autofocus performance, image stabilisation and manufacturing complexity.

Focus breathing exists within this larger system of compromises.

Some lenses are specifically designed to minimise it.

Others may prioritise different characteristics.

Consequently, focus breathing should not automatically be interpreted as a measure of lens quality.

It is better understood as part of the lens's optical behaviour.

This is particularly important when comparing specifications.

Two lenses with the same nominal focal length may not necessarily behave identically when focused at different distances.

Their optical designs can produce different effective fields of view.

The specification tells us what the lens is called.

Actual use tells us how the lens behaves.

The VCP Perspective

For the photographer, this is perhaps the most interesting aspect of the subject.

Photography is often taught in terms of exposure, aperture, shutter speed, ISO, focal length and focus.

Those controls describe what we deliberately do to create an image.

Focus breathing reveals another layer.

It shows us what the optical system is doing while we are making those decisions.

This is increasingly relevant as Canon's RF system develops.

The modern lens is not simply a tube of glass.

It is a highly engineered optical, mechanical and electronic system communicating continuously with the camera.

VCM technology represents one component of that evolution.

Its contribution is not simply faster focusing.

Its potential significance is the increasingly precise control of the optical groups responsible for focusing.

That creates opportunities for lens designers to address phenomena such as focus breathing while simultaneously improving autofocus responsiveness and smoothness.

Conclusion: When Focusing Changes More Than Focus

Focus breathing is a useful reminder that the photographic image is produced by a system rather than by an isolated camera setting.

Changing focus can change the apparent framing.

The phenomenon may be almost invisible in ordinary still photography, yet become immediately apparent during video or deliberate focus transitions.

VCM technology does not, by definition, eliminate focus breathing. The phenomenon remains fundamentally connected to optical and mechanical design.

What VCM can provide is something different: highly responsive and precisely controllable movement of focusing elements.

Combined with sophisticated optical design, independently controlled focusing groups, advanced autofocus algorithms and increasingly intelligent camera-lens communication, this creates greater potential to control what happens to the image while focus changes.

That is ultimately why focus breathing belongs within the broader discussion of Canon's evolving VCM technology.

The future of autofocus is not simply about making the camera focus faster.

It is increasingly about making the entire focusing process more precise, more predictable and less disruptive to the photographer's intended image.

And that takes us back to Creative Vision.

The photographer may think:

“I am changing focus.”

The lens is doing something more complicated.

It is changing the optical geometry through which the scene is being observed.

Understanding that distinction is another step toward understanding not only how modern Canon lenses work, but how the technology can influence the image before the shutter is even released.

This would sit particularly well beside your existing VCM Autofocus work: the earlier essay can explain the focusing technology itself, while this one examines an optical consequence of focusing and how the newer architecture may help manage it.