1. Focal Length:
* What it is: Focal length is measured in millimeters (mm) and determines the magnification and field of view of the lens. It significantly impacts perspective and compression.
* Impact on Portraits:
* Shorter Focal Lengths (35mm, 50mm):
* Pros: Wider field of view, allows you to capture more of the environment, good for environmental portraits (showing the subject in their surroundings), often more affordable.
* Cons: Can introduce distortion, especially at the edges of the frame, making faces appear wider. Requires you to be closer to your subject, which can be uncomfortable for them. Less background blur.
* Mid-Range Focal Lengths (85mm, 105mm):
* Pros: Considered the "classic" portrait range. Good balance between field of view and compression. Provides pleasing facial proportions. Creates a good amount of background blur. Allows for a comfortable distance between you and the subject.
* Cons: Can be more expensive than shorter focal lengths. May not be ideal in tight spaces.
* Longer Focal Lengths (135mm, 200mm, etc.):
* Pros: Strong compression effect, making the background appear closer to the subject. Creates a very shallow depth of field, resulting in significant background blur ("bokeh"). Allows you to work from a greater distance, which can be less intimidating for the subject.
* Cons: Can be bulky and heavy. Requires more space to work effectively. Can amplify camera shake, so a tripod or image stabilization might be necessary. Background blur might be *too* strong, losing context.
* Recommendation: For a starting point, 85mm is widely regarded as an excellent and versatile portrait lens. It offers a good balance of flattering perspective, pleasant background blur, and a comfortable working distance. 50mm is a great budget option if you're just starting out. Experimenting with different focal lengths is encouraged to discover your preferred style.
2. Aperture (f-stop):
* What it is: Aperture refers to the size of the lens opening. A wider aperture (smaller f-number like f/1.4, f/1.8, f/2.8) allows more light to enter the camera, and a narrower aperture (larger f-number like f/8, f/11) lets in less.
* Impact on Portraits:
* Wide Aperture (e.g., f/1.4 - f/2.8):
* Pros: Creates a very shallow depth of field, blurring the background beautifully and isolating the subject. Allows for shooting in low-light conditions without raising the ISO too high.
* Cons: Depth of field is so shallow that it can be challenging to get both eyes in focus, especially with wider apertures. Lens can be more expensive.
* Narrower Aperture (e.g., f/4 - f/8):
* Pros: Greater depth of field, ensuring more of the subject is in focus. Allows for more of the background to be visible, providing context. Lens tends to be less expensive.
* Cons: Less background blur. Requires more light to achieve proper exposure, potentially requiring higher ISO or slower shutter speeds.
* Recommendation: A wide aperture (f/2.8 or wider) is generally preferred for portraits, as it allows for excellent background blur and low-light performance. Consider the trade-offs between shallow depth of field and getting sharp focus on critical features like the eyes. Many photographers use f/2.0 - f/2.8 for a nice balance.
3. Lens Quality (Sharpness, Contrast, Aberrations):
* Sharpness: How well the lens resolves detail. Look for reviews that discuss sharpness, especially at different apertures. Center sharpness is usually good, but edge sharpness can vary.
* Contrast: The difference between the brightest and darkest areas of an image. Good contrast adds depth and richness to your portraits.
* Chromatic Aberration (CA): Color fringing that can appear around high-contrast edges. Good lenses minimize CA.
* Distortion: Straight lines appearing curved in the image. Portrait lenses should ideally have minimal distortion.
* Vignetting: Darkening of the corners of the image. Can be corrected in post-processing.
* Recommendation: Read reviews from reputable sources (e.g., DPReview, LensRentals, Photography Life) to get an idea of a lens's optical performance. Don't automatically assume that the most expensive lens is the best for you.
4. Autofocus Performance:
* Speed and Accuracy: Important for capturing sharp images, especially when photographing moving subjects or using wide apertures. Look for lenses with fast and accurate autofocus systems.
* Quietness: A silent autofocus motor can be beneficial for video recording.
* Recommendation: If you frequently photograph children or pets, or if you plan to shoot video, prioritize a lens with fast and reliable autofocus. Consider lenses with Ultrasonic Motors (USM) or Stepping Motors (STM) for quick and quiet autofocus.
5. Build Quality and Durability:
* Materials: Lenses made with metal barrels tend to be more durable than those made with plastic.
* Weather Sealing: A weather-sealed lens can protect against dust and moisture, making it suitable for outdoor shooting in various conditions.
* Recommendation: If you plan to use your lens frequently and in challenging environments, invest in a well-built and durable lens.
6. Budget:
* New vs. Used: Consider buying a used lens to save money. Reputable used lens dealers often offer warranties and return policies.
* Third-Party Lenses: Sigma, Tamron, and other third-party lens manufacturers offer excellent alternatives to first-party lenses at often lower prices. Research their offerings carefully.
* Recommendation: Determine your budget upfront and stick to it. Prioritize the features that are most important to you (e.g., aperture, sharpness) within your budget. A well-chosen, slightly older, used lens can often outperform a cheaper new one.
7. Camera System Compatibility:
* Lens Mount: Ensure that the lens is compatible with your camera's lens mount (e.g., Canon EF, Nikon F, Sony E, Micro Four Thirds).
* Crop Factor: If you're using a camera with a crop sensor (APS-C), remember that the effective focal length of the lens will be longer. For example, an 85mm lens on an APS-C camera with a 1.5x crop factor will have an effective focal length of 127.5mm.
8. Personal Preference and Shooting Style:
* Experiment: The best way to find the perfect portrait lens is to experiment with different lenses and see what works best for your shooting style and aesthetic. Rent lenses before buying them to try them out.
* Consider your subject: What kind of portraits are you shooting? Headshots, full-body shots, environmental portraits? This will influence your focal length choice.
In summary, here's a quick guide:
* Best Overall: 85mm f/1.8 (or faster if your budget allows) - Great balance of perspective, bokeh, and price.
* Budget-Friendly: 50mm f/1.8 - Versatile and affordable. Requires you to be closer to your subject.
* Environmental Portraits: 35mm f/1.8 (or faster) - Shows the subject in their surroundings.
* Maximum Background Blur: 135mm f/2 (or faster) - Excellent subject isolation. Requires more space.
* Professional Choice: 70-200mm f/2.8 - Versatile zoom with excellent image quality and background blur. Larger and more expensive.
Ultimately, the "perfect" portrait lens is subjective and depends on your individual needs and preferences. By considering these factors and doing your research, you can make an informed decision and choose a lens that will help you create stunning portraits. Good luck!