1. Focal Length: This is arguably the most crucial aspect. Portrait lenses typically fall within the following ranges:
* 85mm (Full-frame equivalent): This is a classic portrait focal length, offering a flattering perspective and pleasing background compression (bokeh). It's a great all-around choice, especially for head-and-shoulders to ¾ length shots. On APS-C cameras, the equivalent focal length will be longer (e.g., a 50mm lens on an APS-C camera will behave similarly to an 85mm on a full-frame).
* 50mm (Full-frame equivalent): A versatile focal length that can work for portraits, but it might require you to be closer to your subject. It offers less background compression than an 85mm. On APS-C, it's a good starting point.
* 135mm (Full-frame equivalent) and beyond (telephoto): These lenses provide even more background compression and allow you to shoot from further away, which can be helpful for environmental portraits or when you want a more intimate feel without being intrusive. They're excellent for isolating your subject.
Consider your shooting style:
* Environmental Portraits: A wider focal length (e.g., 50mm or 85mm) or a zoom lens might be preferable to better incorporate the surroundings.
* Close-up Portraits: An 85mm or longer focal length will generally be better.
2. Aperture: A wide maximum aperture (e.g., f/1.4, f/1.8, f/2) is highly desirable for several reasons:
* Shallow Depth of Field (Bokeh): This creates that pleasing blurry background that's characteristic of professional portraits, drawing attention to the subject.
* Low-Light Performance: A wider aperture lets in more light, allowing you to shoot in lower-light conditions without needing a high ISO (which can introduce noise).
However, wider apertures are generally more expensive. An f/2.8 lens is a good compromise between cost and performance.
3. Image Stabilization (IS) or Vibration Reduction (VR): This feature is helpful for shooting handheld, especially in low light, as it helps to reduce camera shake and produce sharper images.
4. Autofocus: A fast and accurate autofocus system is crucial for capturing sharp portraits, especially when shooting moving subjects.
5. Build Quality and Features: Consider factors like weather sealing (important if you shoot outdoors often), focusing ring feel, and overall build quality.
6. Budget: Portrait lenses can range from a few hundred dollars to several thousand. Set a realistic budget and prioritize the features that are most important to you.
7. Full-frame vs. APS-C: If you have an APS-C camera, remember that the effective focal length will be longer than the stated focal length. A 50mm lens on an APS-C camera will behave like a roughly 75-80mm lens on a full-frame camera.
Lens Types to Consider:
* Prime Lenses: These lenses have a fixed focal length (e.g., 50mm, 85mm, 135mm). They generally offer superior image quality and faster apertures than zoom lenses at a similar price point.
* Zoom Lenses: These lenses offer a range of focal lengths (e.g., 24-70mm, 70-200mm). They are more versatile but often compromise on image quality and maximum aperture compared to prime lenses.
In short: For many, an 85mm f/1.8 prime lens is an excellent starting point due to its balance of cost, image quality, and performance. But the best lens for *you* depends on your specific needs and preferences. Read reviews, compare specifications, and if possible, try out different lenses before making a purchase.