1. Focal Length:
* Understanding Focal Length: Focal length (measured in millimeters - mm) determines the field of view and the perspective of your image. Shorter focal lengths (e.g., 35mm) capture a wider scene, while longer focal lengths (e.g., 200mm) capture a narrower scene, magnifying the subject.
* Common Portrait Focal Lengths & Their Characteristics:
* 35mm: Wider perspective. Good for environmental portraits, showing the subject in their surroundings. Can introduce distortion if used too close to the subject's face.
* Pros: Versatile, good in tight spaces, contextual.
* Cons: Can distort features if used too close, not as much subject isolation.
* 50mm: Considered "normal" and close to how the human eye sees. Good all-around choice, including portraits. More flattering than 35mm.
* Pros: Affordable, versatile, relatively natural perspective.
* Cons: May not provide enough compression for some, may require moving closer to the subject.
* 85mm: A classic portrait lens. Offers excellent subject isolation, flattering perspective, and good compression.
* Pros: Excellent subject isolation, pleasing compression, flattering perspective.
* Cons: Requires more space to work, can be expensive.
* 100mm - 135mm: Even more compression than 85mm. Excellent for headshots and tight portraits, minimizing distortion.
* Pros: Very flattering, great compression, isolates the subject beautifully.
* Cons: Requires a lot of space, less versatile than shorter focal lengths.
* 70-200mm: A popular zoom lens that includes multiple portrait-worthy focal lengths. Provides flexibility and excellent reach.
* Pros: Versatile, allows for different framing without moving, good compression at 200mm.
* Cons: Can be heavy and expensive, might not be as sharp as prime lenses at certain focal lengths.
* 200mm+: Offers extreme compression, ideal for very tight headshots or portraits from a distance.
* Pros: Maximum compression, great for isolating subjects from busy backgrounds.
* Cons: Requires a lot of space, can be difficult to handle due to weight and size, may not be practical for all situations.
* Crop Sensor vs. Full Frame: The sensor size of your camera affects the *effective* focal length.
* Crop Sensor Cameras (e.g., APS-C): Multiply the lens's focal length by the crop factor (usually 1.5x or 1.6x) to get the equivalent focal length on a full-frame camera. For example, a 50mm lens on a camera with a 1.5x crop factor will behave like a 75mm lens.
* Full Frame Cameras: The stated focal length is the actual focal length.
2. Aperture (f-stop):
* Understanding Aperture: Aperture refers to the size of the lens opening, controlling how much light enters the camera and the depth of field (DOF).
* Importance for Portraits: A wider aperture (smaller f-number like f/1.4, f/1.8, f/2.8) creates a shallower depth of field, blurring the background and isolating the subject. This is often desirable for portraits.
* Choosing an Aperture:
* Fast Aperture (f/1.2 - f/2.8): Excellent for blurry backgrounds, low-light shooting, and creating a dreamy look. Requires precise focusing, as the depth of field is very shallow.
* Moderate Aperture (f/3.5 - f/5.6): Offers a good balance between depth of field and background blur. Good for group portraits or when you want some background detail.
* Smaller Aperture (f/8 - f/16): Creates a larger depth of field, keeping more of the scene in focus. Not ideal for isolating the subject.
* Considerations:
* Lens Sharpness: Lenses are often sharpest a stop or two down from their widest aperture. For example, a lens with a maximum aperture of f/1.4 might be sharpest around f/2.0 or f/2.8.
* Price: Lenses with wider maximum apertures (e.g., f/1.4) tend to be more expensive.
3. Image Quality:
* Sharpness: Look for a lens that is sharp across the frame, especially at your desired aperture.
* Chromatic Aberration: Fringing or color distortion, especially around high-contrast edges. Good lenses minimize this.
* Vignetting: Darkening of the corners of the image. Some lenses have more vignetting than others. It can be corrected in post-processing.
* Distortion: Curvature of straight lines in the image. Prime lenses generally have less distortion than zoom lenses.
* Bokeh: The aesthetic quality of the out-of-focus areas in the image. Smooth, creamy bokeh is generally preferred for portraits.
4. Autofocus:
* Speed and Accuracy: Fast and accurate autofocus is crucial for capturing sharp portraits, especially when photographing moving subjects.
* Autofocus Motor: Different lenses use different types of autofocus motors.
* Ultrasonic Motors (USM, HSM, etc.): Generally faster, quieter, and more accurate.
* Stepping Motors (STM, etc.): Smoother and quieter, making them suitable for video recording.
* Manual Focus Override: The ability to manually focus even when autofocus is enabled can be helpful for fine-tuning focus.
5. Build Quality and Handling:
* Durability: Consider the lens's construction and materials. Is it weather-sealed? Will it withstand regular use?
* Weight and Size: A heavy lens can become tiring to use for extended periods.
* Ergonomics: How comfortable is the lens to hold and operate? Are the focus and zoom rings smooth and easy to use?
6. Budget:
* Set a Realistic Budget: Portrait lenses range in price from a few hundred dollars to several thousand. Determine how much you're willing to spend before you start shopping.
* Consider Used Lenses: Buying a used lens can save you money, but be sure to inspect it carefully for any damage or issues.
* Prioritize Key Features: If you're on a tight budget, prioritize the features that are most important to you (e.g., aperture, focal length, sharpness). You might have to compromise on other features like build quality or autofocus speed.
7. Camera System:
* Native Lenses: Lenses designed specifically for your camera system will generally perform better than adapted lenses.
* Lens Mount: Make sure the lens you choose is compatible with your camera's lens mount.
* Third-Party Lenses: Brands like Sigma, Tamron, and Rokinon offer high-quality lenses for various camera systems, often at a lower price than the camera manufacturer's lenses.
8. Test and Rent (If Possible):
* Rent Before You Buy: Renting a lens allows you to try it out in real-world situations before committing to a purchase.
* Test Different Lenses: If possible, test several different lenses to see which one you prefer.
* Compare Images: Take the same photos with different lenses and compare the results to see which lens produces the best images for your style.
Summary Checklist:
1. Decide on Focal Length: Consider the type of portraits you want to take (environmental, headshots, etc.) and the space you'll be working in. Experiment with different focal lengths to see what you prefer.
2. Consider Aperture: Determine how important shallow depth of field is to you.
3. Research Image Quality: Read reviews and compare images taken with different lenses.
4. Evaluate Autofocus: Consider the autofocus speed and accuracy of the lens.
5. Assess Build Quality and Handling: Think about the durability, weight, and ergonomics of the lens.
6. Set a Budget: Determine how much you're willing to spend.
7. Check Camera System Compatibility: Make sure the lens is compatible with your camera.
8. Test and Rent: If possible, rent a lens before you buy it to see if it meets your needs.
By carefully considering these factors, you'll be well on your way to choosing the perfect portrait lens for your photography. Good luck!