1. Focal Length: This is arguably the most important factor.
* 35mm: Wider perspective. Good for environmental portraits, showing the subject within their surroundings. Not as flattering on the face due to potential distortion. More challenging to isolate the subject.
* 50mm: Considered a "standard" focal length, close to human vision. Versatile, works well for full-body and some head-and-shoulder shots. Good balance between isolation and showing context. Can be very affordable, often available with wide apertures (f/1.8, f/1.4).
* 85mm: A classic portrait lens. Compresses perspective slightly, leading to more flattering facial features. Great for headshots and upper-body shots. Provides excellent subject isolation and creamy bokeh.
* 100mm - 135mm: Further compression, very flattering, excellent for headshots. Creates beautiful background blur. Requires more distance from the subject. Can be challenging in small spaces.
* 70-200mm Zoom (at 200mm): Even more compression. Allows for great distance from the subject, which can be helpful for candid or shy subjects. Can create very shallow depth of field and excellent background blur. However, can be large and heavy.
Recommendation: 85mm is a great starting point for dedicated portraiture. If you want more environmental portraits, consider a 50mm or even a 35mm. For headshots and significant background blur, the 85mm, 100mm, or 135mm ranges are ideal.
2. Aperture (f-stop): How wide the lens can open.
* Wider Aperture (e.g., f/1.2, f/1.4, f/1.8, f/2.8):
* Pros: Allows more light in, crucial for low-light photography. Creates a shallower depth of field (more background blur or "bokeh"). Isolates the subject effectively. Can be used for faster shutter speeds.
* Cons: Can be more expensive. Requires more careful focusing due to the shallow depth of field. Image sharpness may be slightly lower at the widest aperture (though often negligible on modern lenses).
* Narrower Aperture (e.g., f/4, f/5.6, f/8):
* Pros: More depth of field, keeping more of the image in focus. Generally sharper overall. Less demanding on focusing accuracy. Often less expensive.
* Cons: Less background blur. Requires more light or higher ISO. May not isolate the subject as effectively.
Recommendation: Aim for a lens with at least f/2.8, ideally wider if your budget allows (f/1.8 or f/1.4). The wider aperture gives you more creative control over depth of field and allows you to shoot in more challenging lighting conditions.
3. Budget: Lenses can range from a few hundred dollars to several thousand.
* Affordable Options: 50mm f/1.8, 85mm f/1.8 (these offer fantastic value for their price)
* Mid-Range Options: 35mm f/1.4, 50mm f/1.4, 85mm f/1.4, 70-200mm f/2.8 (zoom lenses are typically more expensive)
* High-End Options: Specialized portrait lenses (e.g., tilt-shift lenses), high-end prime lenses with very wide apertures (e.g., f/1.2, f/0.95)
Recommendation: Start with an affordable option and upgrade as your needs and budget grow. A 50mm f/1.8 or an 85mm f/1.8 lens is a fantastic way to get started without breaking the bank.
4. Autofocus vs. Manual Focus:
* Autofocus (AF): Convenient, especially for moving subjects or fast-paced shoots. Modern autofocus systems are very accurate.
* Manual Focus (MF): Requires more skill and practice. Can be useful for very precise focusing or in situations where autofocus struggles (e.g., low light, low contrast). Often found on older lenses or specialized lenses.
Recommendation: For most portrait photographers, autofocus is essential. Look for a lens with fast and accurate autofocus. Manual focus can be a fun skill to learn, but it's not necessary for most portrait work.
5. Image Stabilization (IS/VR):
* Helps to reduce camera shake, allowing you to shoot at slower shutter speeds without motion blur. Especially helpful in low-light conditions or when shooting handheld.
Recommendation: Image stabilization is a nice-to-have, but not essential for portrait lenses, especially if you're shooting with a camera that has in-body image stabilization (IBIS). It's more important for longer focal lengths and when shooting video.
6. Crop Sensor vs. Full Frame:
* Crop Sensor (APS-C): Has a smaller sensor than full frame. This affects the effective focal length of the lens. A 50mm lens on a crop sensor camera will have a field of view equivalent to approximately 75mm - 80mm (depending on the crop factor, usually 1.5x or 1.6x).
* Full Frame: Has a larger sensor. Lenses perform as their advertised focal length.
Important Note: Lenses designed for full-frame cameras can be used on crop sensor cameras, but lenses designed specifically for crop sensor cameras cannot be used on full-frame cameras.
Recommendation: When choosing a lens, consider the crop factor of your camera if you're using a crop sensor camera. For example, if you want an 85mm equivalent field of view on a crop sensor camera with a 1.6x crop factor, you'll need a lens with a focal length of approximately 53mm (85 / 1.6 = 53.125).
7. Lens Build Quality:
* Consider the materials used and the overall construction. A well-built lens will be more durable and resistant to dust and moisture. Weather sealing is a valuable feature, especially if you plan to shoot outdoors.
8. "Character" and Rendering:
* This is a more subjective factor. Some lenses have a unique "look" to them, characterized by the way they render out-of-focus areas (bokeh), their color rendition, and their overall sharpness. Read reviews and look at sample images to get a sense of the lens's character.
9. Your Personal Style and Subject:
* Consider the types of portraits you like to shoot. Do you prefer close-up headshots, or do you like to show the subject in their environment? Are you shooting indoors or outdoors? Think about the specific needs of your portrait subjects (e.g., skin tones, hair details).
In Summary, Here's a Step-by-Step Guide:
1. Determine your preferred focal length range: Based on the type of portraits you want to shoot (headshots, full-body, environmental). Consider the crop factor of your camera if applicable.
2. Set a budget: This will narrow down your options considerably.
3. Prioritize aperture: Aim for a lens with at least f/2.8, wider if possible.
4. Consider autofocus: Ensure the lens has fast and accurate autofocus.
5. Read reviews and look at sample images: Get a sense of the lens's image quality, sharpness, and bokeh.
6. Rent or borrow if possible: Try out different lenses before you buy. This is the best way to find the perfect fit for your needs and style.
Example Scenarios:
* Beginner with a limited budget: 50mm f/1.8 or 85mm f/1.8 (depending on your camera system).
* Serious amateur wanting to upgrade: 85mm f/1.4 or 70-200mm f/2.8.
* Professional photographer: A range of lenses to cover different situations (e.g., 35mm f/1.4, 50mm f/1.4, 85mm f/1.4, 70-200mm f/2.8).
Choosing the right portrait lens is an investment. Take your time, do your research, and don't be afraid to experiment. Happy shooting!