1. Focal Length: This is arguably the most crucial factor. Focal length dictates the field of view and, more importantly, the compression of features.
* Shorter Focal Lengths (e.g., 35mm, 50mm):
* Pros: Wider field of view, allows you to include more of the environment in your portraits. Great for environmental portraits that tell a story about the subject's surroundings. Can feel more intimate.
* Cons: Can cause distortion, especially with closer shots. May require you to get uncomfortably close to your subject. Flattens features less than longer lenses.
* Good for: Environmental portraits, street portraits, documentary-style portraits, capturing a sense of place.
* "Standard" Portrait Lengths (e.g., 50mm, 85mm):
* Pros: Widely considered the classic portrait focal lengths. 50mm offers a natural perspective, close to human vision. 85mm is often considered the "ideal" portrait lens, offering excellent subject isolation and flattering compression.
* Cons: 50mm might still require you to be relatively close to your subject. 85mm can require more space to work.
* Good for: Versatile, suitable for a wide range of portrait styles, from headshots to half-body shots.
* Longer Focal Lengths (e.g., 100mm, 135mm, 200mm):
* Pros: Offers strong compression, making facial features appear more balanced and flattering. Excellent background separation (bokeh). Allows you to work from a greater distance, which can make subjects feel more comfortable.
* Cons: Can feel isolating, minimizing the background. Requires more space to work. Longer lenses can amplify camera shake.
* Good for: Headshots, close-ups, isolating the subject, creating a shallow depth of field.
2. Aperture (f-stop): This controls the amount of light that enters the lens and, critically, the depth of field.
* Wider Aperture (e.g., f/1.2, f/1.4, f/1.8, f/2.8):
* Pros: Creates a very shallow depth of field, resulting in a blurred background (bokeh). Excellent in low-light situations. Allows for faster shutter speeds.
* Cons: Can be more expensive. Extremely shallow depth of field can be challenging to nail focus, especially at wide apertures.
* Good for: Isolating the subject, creating a dreamy and artistic look, shooting in low light.
* Narrower Aperture (e.g., f/4, f/5.6, f/8):
* Pros: Greater depth of field, ensuring more of the subject is in focus. Useful when you want to include more of the background or need more forgiving focus.
* Cons: Requires more light. May not achieve as much background blur.
* Good for: Group portraits, environmental portraits, when you want more sharpness throughout the image.
3. Image Stabilization (IS/VR/OSS): Important, especially for longer focal lengths and shooting in low light. Helps reduce camera shake, resulting in sharper images.
4. Autofocus Performance: Critical for capturing sharp images, especially with moving subjects or when shooting at wide apertures. Consider the speed and accuracy of the autofocus system. Check reviews for specific lenses and cameras.
5. Build Quality and Weather Sealing: If you plan to shoot in various conditions, a robust build and weather sealing are important for protecting your lens from dust, moisture, and other elements.
6. Budget: Lens prices vary significantly. Determine your budget before you start looking, and be realistic about what you can afford. Consider buying used lenses in good condition.
7. Camera Sensor Size (Full-Frame vs. Crop Sensor):
* Full-Frame (35mm): The focal length listed on the lens is what you get. A 50mm lens is a 50mm lens.
* Crop Sensor (APS-C, etc.): You need to factor in the crop factor (e.g., 1.5x for Nikon, 1.6x for Canon). A 50mm lens on an APS-C camera will have a field of view equivalent to a 75mm or 80mm lens on a full-frame camera. This means you'll need a shorter focal length lens to achieve the same field of view as a full-frame camera. For example, a 35mm lens on an APS-C camera is a good equivalent to a 50mm lens on a full-frame camera.
8. Bokeh Quality: The quality of the out-of-focus areas (bokeh) is important for portraits. Some lenses produce smooth, creamy bokeh, while others produce harsh or distracting bokeh. Look for lenses with rounded aperture blades for smoother bokeh.
9. Lens Aberrations (Chromatic Aberration, Vignetting, Distortion): All lenses have some degree of aberration. Chromatic aberration (color fringing) can be corrected in post-processing, but excessive distortion can be more problematic. Look for lenses with good correction of these issues.
10. Testing and Renting:
* Rent before you buy: Renting lenses allows you to try them out in real-world conditions before committing to a purchase.
* Test in a store: If possible, test lenses in a store to get a feel for their handling and image quality.
Recommendations (General Guidelines):
* Budget-Friendly:
* 50mm f/1.8: A classic and affordable option, great for beginners. Available for most camera systems. Excellent value for the price.
* 35mm f/1.8: A versatile choice, especially for environmental portraits and crop sensor cameras.
* Mid-Range:
* 85mm f/1.8: A highly recommended portrait lens that offers excellent subject isolation and flattering compression.
* 50mm f/1.4: A step up in aperture from the f/1.8, providing shallower depth of field and better low-light performance.
* High-End:
* 85mm f/1.4: The ultimate portrait lens, offering exceptional image quality, creamy bokeh, and excellent low-light performance.
* 70-200mm f/2.8: A versatile zoom lens that can be used for portraits, sports, and other types of photography. Provides a range of focal lengths and excellent image quality.
* 135mm f/2: A longer prime lens known for its exceptional sharpness and beautiful bokeh.
Key Questions to Ask Yourself:
* What kind of portraits do I want to shoot? (Headshots, environmental, full-body, etc.)
* What is my budget?
* What camera system do I use?
* What is more important to me: wide aperture or zoom versatility?
* Do I primarily shoot indoors or outdoors?
* How much background blur do I want?
* Do I prefer to work close to my subject, or do I prefer to maintain more distance?
By carefully considering these factors and doing your research, you can choose the perfect portrait lens to suit your needs and help you create stunning images. Remember that there is no single "best" lens – the ideal choice depends on your individual style and preferences. Good luck!