Have you ever noticed that the field of view of your lens subtly changes as you adjust the focus? This phenomenon, known as focus breathing, is more prevalent in some lenses than others. It occurs because the effective focal length of the lens varies slightly as the focusing elements move internally. Understanding the underlying causes of focus breathing is essential for photographers and videographers who require consistent framing throughout their work.
Understanding Focus Breathing
Focus breathing, also referred to as lens breathing, is a characteristic of certain lenses where the magnification appears to change as the focus distance is altered. This change is not a true change in focal length, but rather an apparent shift in the field of view. It becomes particularly noticeable when racking focus from a close subject to a distant one, or vice versa.
This effect is often more pronounced in zoom lenses, but it can also be present in prime lenses to varying degrees. The design and construction of the lens play a significant role in determining the extent to which focus breathing is apparent.
Factors Contributing to Focus Breathing
Several factors contribute to why some lenses exhibit more focus breathing than others. Lens design, internal focusing mechanisms, and manufacturing tolerances all play a role.
Lens Design: The optical formula of a lens, including the arrangement and types of lens elements, significantly impacts focus breathing. Some designs are inherently more prone to it.
Internal Focusing (IF) Systems: Lenses with internal focusing systems, where only internal elements move during focusing, can sometimes exhibit more noticeable focus breathing. This is because the movement of these elements affects the effective focal length more directly.
Floating Elements: Some lenses incorporate floating elements to improve close-focus performance. However, the movement of these elements can also contribute to focus breathing.
Manufacturing Tolerances: Even slight variations in the manufacturing process can affect the precision of lens element placement, which can, in turn, influence the amount of focus breathing.
Impact of Focus Breathing on Photography and Videography
Focus breathing can have several implications for both photographers and videographers. While it might be negligible in some situations, it can be a significant issue in others.
Photography
For photographers, focus breathing is generally less problematic. However, it can still be a concern in certain scenarios:
Macro Photography: In macro photography, where precise framing is crucial, even slight changes in magnification due to focus breathing can be undesirable.
Focus Stacking: When focus stacking images to increase depth of field, focus breathing can introduce inconsistencies in the framing, making the stacking process more challenging.
Videography
In videography, focus breathing is often a more significant concern due to its impact on the visual flow of a scene.
Rack Focusing: When performing rack focusing (shifting focus from one subject to another), the change in field of view can be distracting and unprofessional.
Interviews and Dialogue Scenes: In interviews or dialogue scenes, where the camera might subtly adjust focus to maintain sharpness on the subject’s face, focus breathing can create an unwanted “zooming” effect.
Visual Consistency: Maintaining consistent framing is crucial for visual storytelling. Focus breathing can disrupt this consistency, making editing and post-production more difficult.
Identifying Focus Breathing
Identifying whether a lens exhibits significant focus breathing is relatively straightforward. Here’s a simple method:
- Set up a scene with a subject at a close distance and another subject at a far distance.
- Mount the lens on a camera and frame the scene.
- Record a video while slowly racking focus from the close subject to the far subject, and then back again.
- Review the footage and observe whether the field of view appears to change during the focus transitions. If the scene seems to zoom in or out as the focus changes, the lens exhibits focus breathing.
Mitigating Focus Breathing
While focus breathing is an inherent characteristic of some lenses, there are several techniques to mitigate its impact:
Choose Lenses with Minimal Focus Breathing: Research and select lenses known for minimal focus breathing, especially for videography work. Lens reviews and online forums often provide information on this characteristic.
Adjust Framing After Focusing: If precise framing is essential, adjust the camera position slightly after focusing to compensate for any changes in the field of view.
Use a Longer Focal Length: When possible, using a longer focal length can minimize the apparent effect of focus breathing, as the changes in magnification will be less noticeable.
Crop in Post-Production: In videography, you can subtly crop the footage in post-production to stabilize the framing and minimize the visual impact of focus breathing.
Maintain Subject Distance: Try to maintain a more consistent distance between the camera and the subject to minimize the need for large focus adjustments.
Lenses and Focus Breathing: Some Examples
The prevalence of focus breathing varies significantly across different lens models. Some lenses are specifically designed to minimize this effect, while others exhibit it more noticeably.
Lenses with Minimal Focus Breathing: Some cine lenses and high-end photography lenses are engineered to minimize focus breathing, often at a higher cost. These lenses are typically preferred for professional videography.
Lenses with Noticeable Focus Breathing: Many kit lenses and consumer-grade zoom lenses tend to exhibit more noticeable focus breathing. While this might not be a major issue for casual photography, it can be a limitation for more demanding applications.
Frequently Asked Questions (FAQ)
What exactly is focus breathing in a lens?
Focus breathing is the apparent change in focal length (and thus, field of view) that occurs as a lens is focused from one distance to another. It’s caused by the internal movement of lens elements during focusing.
Is focus breathing more common in zoom lenses or prime lenses?
Focus breathing can occur in both zoom and prime lenses, but it is generally more noticeable in zoom lenses due to their complex optical designs and larger focusing ranges. Some prime lenses, however, are also known to exhibit significant focus breathing.
Does focus breathing affect image quality?
Focus breathing primarily affects the framing and composition of an image or video. It doesn’t directly degrade image sharpness or other aspects of image quality. However, the change in field of view can be visually distracting, especially in video.
Can focus breathing be corrected in post-production?
While you can’t completely eliminate focus breathing in post-production, you can mitigate its effects by subtly cropping and stabilizing the footage to maintain a more consistent framing. This approach is more effective for minor cases of focus breathing.
Are there lenses specifically designed to minimize focus breathing?
Yes, some high-end cine lenses and certain photography lenses are engineered with designs that minimize focus breathing. These lenses often come at a premium price but are highly valued by professional videographers and cinematographers.
