1. Compression:
* Longer Focal Lengths (85mm, 100mm, 135mm, 200mm+):
* Compressed Features: Longer focal lengths compress the distance between the subject's features. This means the nose appears less prominent, the ears seem closer to the face, and the face appears more flattened in terms of depth.
* Subject Isolation: Longer focal lengths also compress the background, making it appear closer to the subject. This helps isolate the subject and creates a shallow depth of field (blurred background) more easily.
* More Flattering (Generally): Because of the compression, longer focal lengths are often considered more flattering. They tend to make the face look slimmer and more balanced, minimizing perceived flaws like a slightly larger nose.
* Downsides: You need more distance between you and the subject, which can make communication feel a little less intimate.
* Shorter Focal Lengths (24mm, 35mm, 50mm):
* Expanded Features: Shorter focal lengths expand the distance between features. This can make the nose appear larger, the face rounder, and the ears further back.
* Exaggerated Perspective: Short focal lengths emphasize the perspective, making the distance between near and far objects seem greater. This can lead to distortion, particularly at the edges of the frame.
* Less Flattering (Usually): The expansion and distortion can make the face appear less conventionally attractive, especially close-up.
* Wider Field of View: You can capture more of the environment around the subject. This can be useful for environmental portraits that tell a story.
* Upsides: You can work in tighter spaces and often get a more intimate feel due to proximity.
2. Perspective:
While related to compression, perspective is slightly different. It's about the relative size and placement of objects in the frame based on their distance from the camera.
* Longer Focal Lengths: Tend to have a more orthographic perspective, meaning parallel lines appear more parallel in the image, reducing distortion.
* Shorter Focal Lengths: Tend to have a more curvilinear perspective, meaning parallel lines converge more dramatically, increasing distortion, especially at the edges of the frame.
Think of it this way:
* Telephoto lens (long focal length): Feels like you're flattening the face onto a plane. Imagine looking at a face pressed against a pane of glass.
* Wide-angle lens (short focal length): Feels like you're stretching the face away from you. Imagine pulling a face out of shape.
Examples and Common Focal Length Choices:
* 24mm-35mm: Often used for environmental portraits, capturing a wide scene with the subject within it. Not usually recommended for close-up portraits due to potential distortion of facial features.
* 50mm: A popular "normal" focal length. It offers a relatively natural perspective, close to what the human eye sees. Good for portraits that include a decent amount of the surroundings. Can still introduce slight distortion if you get too close.
* 85mm: A very common and well-regarded portrait lens. Offers a good balance of compression, subject isolation, and a flattering perspective. A safe and versatile choice.
* 100mm - 135mm: Provides even more compression and subject isolation. Excellent for creating a dreamy, blurred background ("bokeh") and for emphasizing specific facial features. Requires a good amount of distance between you and the subject.
* 200mm+: Even more compression, but can become impractical for close-up portraits in many situations due to the extreme distance required. Often used for headshots from a distance or for wildlife photography where the subject is far away.
Key Considerations When Choosing a Focal Length:
* Desired Look: Are you going for a flattering, compressed look or a more dramatic, environmental portrait?
* Shooting Space: Do you have enough room to move back when using a longer lens?
* Subject's Features: Consider the subject's facial features. A person with a naturally small nose might not benefit from further compression.
* Aperture: The wider the aperture (smaller f-number, like f/1.8 or f/2.8), the shallower the depth of field, which will blur the background more. Longer focal lengths with wide apertures are excellent for isolating the subject.
* Personal Preference: Experiment and find what works best for you and your style. There are no hard and fast rules!
In summary, focal length is a powerful tool in portraiture. By understanding compression and perspective, you can choose the right lens to create the desired look and capture the best possible image of your subject.