1. Understand the Core Concepts:
* Focal Length: This determines the field of view and how much you can fit into the frame. It also impacts compression and perspective.
* Shorter Focal Lengths (e.g., 35mm, 50mm): Wider field of view, good for environmental portraits showing the subject within their surroundings. Can introduce some distortion closer to the edges.
* Medium Focal Lengths (e.g., 85mm): Classic portrait range. Offers good subject isolation, flattering perspective, and a manageable working distance.
* Longer Focal Lengths (e.g., 135mm, 200mm): Great for isolating the subject, compressing the background, and maintaining a comfortable distance. Can require more space to work in.
* Aperture: This controls the amount of light entering the lens and affects depth of field (the area in focus).
* Wide Apertures (e.g., f/1.2, f/1.4, f/1.8, f/2.8): Allow more light, enabling faster shutter speeds in low light. Create shallow depth of field, blurring the background and emphasizing the subject.
* Narrower Apertures (e.g., f/4, f/5.6, f/8): Allow less light, requiring slower shutter speeds or higher ISO. Create greater depth of field, keeping more of the scene in focus.
* Sensor Size (Crop Factor): The sensor size of your camera significantly affects the effective focal length. A crop sensor camera (APS-C, Micro Four Thirds) will make a lens appear "longer" than it would on a full-frame camera. For example, a 50mm lens on an APS-C camera with a 1.5x crop factor will behave like a 75mm lens on a full-frame camera. Keep this in mind when considering focal lengths.
* Sharpness: A sharp lens is crucial for capturing fine details. Look for lenses that are sharp across the frame, even at wider apertures. Read reviews and look at sample images to assess sharpness.
* Bokeh: The quality of the out-of-focus areas (bokeh) is important for creating a pleasing and professional look. Look for lenses with smooth, creamy bokeh, free from harsh highlights or distracting shapes.
* Build Quality & Autofocus: Consider the lens's durability, weather sealing (if needed), and autofocus speed and accuracy. A reliable lens will last longer and perform better in various conditions.
2. Consider Your Shooting Style and Preferences:
* Type of Portraits:
* Headshots: 85mm or 100mm (or equivalent on crop sensor).
* Half-body Portraits: 50mm, 85mm, 100mm.
* Full-body Portraits: 35mm, 50mm, 85mm.
* Environmental Portraits: 24mm, 35mm, 50mm.
* Subject: Are you primarily photographing individuals, couples, or groups? Different focal lengths work better for different group sizes.
* Environment: Do you primarily shoot indoors or outdoors? How much space do you have to work with? Shooting in tight spaces may require wider focal lengths.
* Lighting: Do you shoot in natural light or use artificial lighting? Wide aperture lenses are essential for low-light situations.
* Budget: Portrait lenses range in price from a few hundred dollars to several thousand. Set a budget and look for the best value within that range.
3. Popular Portrait Lens Choices (General Guidelines):
* Full-Frame:
* 50mm f/1.8 or f/1.4: Versatile, affordable, and good in low light. Great starting point.
* 85mm f/1.8 or f/1.4: Classic portrait lens, excellent subject isolation, flattering perspective.
* 135mm f/2 or f/2.8: Excellent subject isolation, beautiful bokeh, requires more working distance.
* 35mm f/1.4 or f/1.8: Good for environmental portraits, shows the subject in context.
* 70-200mm f/2.8: Versatile zoom lens, excellent for various portrait situations, but expensive.
* APS-C (Crop Sensor):
* 35mm f/1.8 (approximately 50mm equivalent): Similar to a 50mm on full-frame.
* 50mm f/1.8 (approximately 75mm equivalent): Closer to a classic portrait focal length.
* 50-135mm f/2.8 (or similar): Provides a range of useful focal lengths.
* Micro Four Thirds:
* 25mm f/1.7 (approximately 50mm equivalent): Affordable and versatile.
* 42.5mm f/1.7 (approximately 85mm equivalent): A classic portrait focal length.
* 45mm f/1.8 (approximately 90mm equivalent): Another excellent option.
4. Research and Reviews:
* Read reviews from reputable sources: DPReview, Ken Rockwell (opinions vary!), LensRentals.com, and other photography websites.
* Watch video reviews on YouTube: Look for reviews that discuss image quality, autofocus performance, and handling.
* Check sample images online: Search for images taken with the lens you're considering to get a feel for its image quality and bokeh.
5. Rent Before You Buy (Highly Recommended):
* Rent lenses from companies like LensRentals.com, BorrowLenses.com, or your local camera store. This allows you to try out different focal lengths and apertures with your own camera and shooting style before making a purchase. This is the *best* way to find the perfect lens for *you*.
6. Factors Beyond the Lens:
* Lighting: Good lighting is crucial for portrait photography, regardless of the lens you use. Invest in lighting equipment or learn how to utilize natural light effectively.
* Composition: Learn the fundamentals of composition to create visually appealing portraits.
* Post-Processing: Editing your images is an essential part of the portrait photography workflow. Learn how to use software like Adobe Lightroom or Capture One to enhance your images.
In summary, choosing the perfect portrait lens is a balance between understanding the technical aspects of lenses, considering your shooting style and preferences, researching different options, and ideally, renting before you buy. There's no single "best" lens – it's about finding the one that best suits your individual needs and creative vision.