Understanding the Basics
* Focal Length: The distance (in millimeters) between the lens's optical center and the image sensor when the lens is focused at infinity.
* Field of View: The area that the lens captures. Shorter focal lengths have a wider field of view; longer focal lengths have a narrower field of view.
* Compression: A perceptual effect where the distance between objects appears reduced with longer focal lengths. This is *not* actually compressing the scene, but rather changing the perspective and relative sizes.
* Perspective Distortion: How the relative sizes and distances of objects within the scene are rendered. Changes in focal length alone do *not* cause perspective distortion. Perspective distortion is solely determined by the *distance* to the subject.
How Focal Length Affects Facial Features
* Shorter Focal Lengths (e.g., 24mm, 35mm):
* Wider Field of View: Captures more of the background, which can be useful for environmental portraits (showing the person in context).
* Exaggerated Perspective (when close to the subject): If you move close to the subject to fill the frame with a wide-angle lens, you introduce perspective distortion. This means:
* Features Closest to the Lens Appear Larger: The nose becomes disproportionately large.
* Features Further Away Appear Smaller: The ears appear smaller, and the face might appear thinner or elongated.
* Rounding of the Face: The sides of the face can seem to curve inward more noticeably.
* Generally Unflattering: Typically avoided for close-up portraits unless you're going for a specific, stylized effect. They tend to emphasize flaws and make the face look less balanced.
* "Normal" Focal Lengths (e.g., 50mm):
* Neutral Perspective (from a reasonable distance): If you move back far enough to frame the face, a 50mm lens offers a relatively natural and balanced rendering. Perspective is less exaggerated.
* Good General-Purpose Portrait Lens: A good starting point for learning portraiture.
* Slightly Flattering: Doesn't overly distort or exaggerate features, making it a more reliable choice.
* Longer Focal Lengths (e.g., 85mm, 100mm, 135mm):
* Narrower Field of View: Focuses the viewer's attention on the subject.
* Compressed Perspective (when farther away): If you move farther away from the subject, a longer focal length will still fill the frame, but it will result in compressed perspective:
* Features Appear More Proportional: The relative size of the nose, ears, and other features seems more accurate.
* Shallower Depth of Field: Blurs the background more effectively, isolating the subject.
* The face looks 'flatter': The distance between the nose and ears appears less, and the face appears somewhat 'flattened' from front to back. This is often perceived as more flattering.
* Rounded Faces Appear Slimmer: The compression can make rounder faces appear slightly narrower.
* More Flattering in Many Cases: The compressed perspective tends to smooth out imperfections and create a more aesthetically pleasing result. The greater subject-background separation also helps.
* Increased Working Distance: Requires you to stand further away from the subject, which can be beneficial for candid shots or for making the subject feel more comfortable.
* Very Long Focal Lengths (e.g., 200mm+):
* Extreme Compression: Creates a very flat perspective, almost like a cardboard cutout.
* Can Look Unnatural: While flattering, extremely long focal lengths can sometimes create an unnatural or stylized look.
* Challenging to Use: Requires a lot of space between you and the subject, and can be difficult to handhold without image stabilization.
Key Takeaways and Practical Advice:
* Distance Matters More Than Focal Length for Perspective: Perspective distortion is caused by your *distance* to the subject, not the focal length itself. If you want to change the perspective, change your distance. The focal length simply allows you to maintain the same framing while changing your distance.
* Focal Length Choice is a Balancing Act: Consider the environment, your desired level of subject isolation, and the overall look you want to achieve.
* Experiment! The best way to understand the effects of different focal lengths is to try them out yourself. Take the same portrait at various focal lengths (adjusting your distance each time to maintain the same framing) and compare the results.
* Consider Your Subject's Features: Some focal lengths might be more flattering for certain face shapes or features than others.
* Don't Be Afraid to Break the Rules: While these are general guidelines, ultimately the best focal length for a portrait depends on your artistic vision and the specific circumstances.
In summary, focal length isn't about "physically" changing the face, but about how it's rendered in the photograph. By understanding the effects of different focal lengths and the relationship between distance, perspective, and compression, you can choose the right lens to create flattering and compelling portraits.