1. Focal Length: This is the most critical factor.
* 35mm:
* Pros: Versatile, good for environmental portraits, captures more of the scene, can be used in tighter spaces.
* Cons: Can distort features slightly if used too close, not as much background compression.
* Best for: Telling a story, capturing context, casual portraits in natural settings.
* 50mm:
* Pros: Close to how the human eye sees, affordable, versatile for both portraits and other types of photography.
* Cons: Requires you to move around more to compose your shots, not as much background compression as longer lenses.
* Best for: Beginners, all-around portraiture, situations where you want a natural look.
* 85mm:
* Pros: Classic portrait focal length, flattering perspective, good background compression, excellent subject isolation.
* Cons: Requires more distance from the subject, can be less versatile for other types of photography, may be too long for indoor shoots.
* Best for: Classic headshots, isolating the subject, creating a shallow depth of field. Considered by many the "ideal" portrait focal length.
* 100-135mm:
* Pros: Excellent background compression, very flattering perspective, smooth bokeh, great for tight headshots.
* Cons: Requires even more distance, can be difficult to use in tight spaces, potentially requires a tripod for stability.
* Best for: Formal portraits, headshots, studio work, isolating specific features.
* 70-200mm (Zoom):
* Pros: Versatile range, allows you to adjust your focal length quickly, good image quality on higher-end versions.
* Cons: Can be heavy and expensive, may not be as sharp as prime lenses.
* Best for: Events, weddings, situations where you need flexibility, capturing candid moments from a distance.
In summary, the longer the focal length, the more compressed the background will be and the further away you'll need to be from your subject.
2. Aperture (f-stop): This controls the amount of light entering the lens and affects depth of field.
* Wide Aperture (e.g., f/1.2, f/1.4, f/1.8, f/2.8):
* Pros: Creates a shallow depth of field (blurry background), allows more light into the camera (good for low-light situations), enhances subject isolation.
* Cons: Can be more difficult to nail focus precisely, more expensive lenses.
* Narrow Aperture (e.g., f/5.6, f/8, f/11):
* Pros: Creates a wider depth of field (more of the scene in focus), easier to achieve sharp focus.
* Cons: Less background blur, requires more light, less subject isolation.
For portraits, a wide aperture is generally preferred to create a pleasing background blur (bokeh) and isolate the subject. However, consider how much of your subject you want in focus. For group portraits, you'll likely need a narrower aperture.
3. Lens Quality (Sharpness, Distortion, Aberrations):
* Sharpness: Look for lenses that produce sharp images, especially at wider apertures. Read reviews and look at sample images.
* Distortion: Some lenses can distort straight lines, which can be unflattering in portraits. Prime lenses generally have less distortion than zoom lenses.
* Chromatic Aberration (Color Fringing): This appears as colored fringes around high-contrast edges. Good lenses minimize this.
* Bokeh: The quality of the background blur. Some lenses produce smoother, more pleasing bokeh than others. This is highly subjective.
4. Autofocus Performance:
* Speed: How quickly the lens can focus on the subject. Important for capturing moving subjects or working in dynamic situations.
* Accuracy: How reliably the lens can achieve and maintain focus on the desired point.
* Quietness: Some autofocus systems are quieter than others, which is important for video recording.
5. Build Quality and Durability:
* Construction: Look for lenses with sturdy construction that can withstand wear and tear.
* Weather Sealing: Consider weather-sealed lenses if you plan to shoot outdoors in challenging conditions.
6. Budget:
* Price Range: Portrait lenses range in price from a few hundred dollars to several thousand. Consider how much you're willing to spend.
* Value: Consider the value for money. A more expensive lens might offer better image quality, autofocus performance, and build quality, but a cheaper lens might be perfectly adequate for your needs.
7. Prime vs. Zoom Lens:
* Prime Lenses:
* Pros: Generally sharper, faster aperture, lighter, often less expensive than comparable zoom lenses.
* Cons: Fixed focal length, requires you to move around to compose your shots.
* Zoom Lenses:
* Pros: Versatile, allows you to adjust your focal length quickly, convenient.
* Cons: Generally not as sharp as prime lenses, slower aperture, heavier, often more expensive.
For ultimate image quality and shallow depth of field, prime lenses are generally preferred for portraiture. However, zoom lenses offer more flexibility, especially for events or situations where you can't move around freely.
8. Camera System:
* Compatibility: Choose a lens that is compatible with your camera's mount. Different camera brands (Canon, Nikon, Sony, etc.) have different lens mounts.
* Crop Sensor vs. Full Frame: If you have a crop sensor camera, you'll need to factor in the crop factor when calculating the effective focal length of the lens. For example, an 85mm lens on a camera with a 1.5x crop factor will have an effective focal length of 127.5mm. Many manufacturers make lenses specifically for crop sensor cameras.
9. Image Stabilization (IS or VR):
* Helpful for shooting handheld, especially in low light or with longer focal lengths. Can allow you to use slower shutter speeds without blur.
Steps to Choose Your Lens:
1. Determine Your Budget: How much are you willing to spend?
2. Consider Your Style: Do you prefer environmental portraits, classic headshots, or something in between?
3. Identify Your Most Common Shooting Scenarios: Where will you be shooting (indoors, outdoors, studio)?
4. Choose a Focal Length Range: Based on your style and scenarios, narrow down your preferred focal length(s).
5. Prioritize Aperture: Determine the widest aperture you need for your desired depth of field.
6. Research Lens Options: Read reviews, compare specifications, and look at sample images. DPReview.com, LensRentals.com, and various photography forums are good resources.
7. Rent or Borrow (If Possible): The best way to decide if a lens is right for you is to try it out in person. Many camera stores or online rental services allow you to rent lenses.
8. Make Your Purchase: Once you've found the perfect lens, buy it from a reputable dealer.
In summary, the "perfect" portrait lens is a subjective choice. Consider your budget, shooting style, and the type of portraits you want to create. Experiment, research, and try before you buy to find the lens that works best for you.