1. Aperture (f-number):
* The Key Factor: Aperture is the size of the lens opening. A wider aperture (smaller f-number like f/1.8, f/2.8, f/4) lets in more light and creates a shallower depth of field, resulting in a blurrier background.
* Example: Shooting at f/1.8 will give you a much blurrier background than shooting at f/8.
* Considerations:
* Lens Quality: Lenses with wider maximum apertures (e.g., f/1.4, f/1.8, f/2.8) are generally more expensive, but they are essential for achieving extreme background blur.
* Sharpness: Some lenses may be slightly softer at their widest apertures. You may need to stop down slightly (e.g., from f/1.8 to f/2) to achieve optimal sharpness on your subject's face.
* Focus Accuracy: Shallow depth of field requires very precise focusing. Use single-point autofocus and carefully place the focus point on your subject's eye.
2. Focal Length:
* Longer Focal Lengths = More Blur: A longer focal length (e.g., 85mm, 135mm, 200mm) compresses the background and magnifies any blur that is present.
* Why it works: Longer lenses increase the magnification of out-of-focus elements, making them appear larger and blurrier.
* Typical Portrait Lenses: 50mm, 85mm, and 135mm lenses are popular choices for portraits. The 85mm is often considered ideal for flattering proportions and background blur.
* Crop Sensor Considerations: If you're using a camera with a crop sensor, you'll need to multiply the focal length by the crop factor (e.g., 1.5x for Nikon DX, 1.6x for Canon APS-C) to get the equivalent focal length on a full-frame camera. For example, a 50mm lens on a 1.6x crop sensor camera is equivalent to an 80mm lens on a full-frame camera.
3. Subject-to-Background Distance:
* Greater Distance = More Blur: The further your subject is from the background, the blurrier the background will appear.
* How to Achieve:
* Position your subject away from walls, trees, or other distracting elements.
* Look for backgrounds that are naturally distant, such as a field or a forest in the distance.
4. Camera-to-Subject Distance:
* Closer Distance = More Blur: The closer you are to your subject, the shallower the depth of field, and the blurrier the background will become.
* Balancing Act: You need to balance this with your chosen focal length. Getting too close with a wide-angle lens can distort your subject's features. Longer focal lengths allow you to be further back while still achieving a blurred background.
5. Sensor Size:
* Larger Sensor = More Blur Potential: Cameras with larger sensors (e.g., full-frame) generally produce shallower depth of field and more pleasing background blur than cameras with smaller sensors (e.g., APS-C, Micro Four Thirds).
* Reason: For a given field of view, you need a longer focal length with a larger sensor, which contributes to increased background blur.
In Summary: The Trifecta for Bokeh
The biggest contributors to background blur are:
* Wide Aperture (Low f-number)
* Long Focal Length
* Large Subject-to-Background Distance
Practical Tips and Considerations:
* Focus Carefully: With a shallow depth of field, precise focus is crucial. Use single-point autofocus and focus on your subject's eyes. Consider using back-button focus.
* Composition: Pay attention to your composition. A blurred background can be beautiful, but it shouldn't be the only thing in the picture.
* Background Elements: Look for backgrounds with interesting textures, colors, or light patterns. These elements will create more pleasing bokeh. Avoid messy or distracting backgrounds, even when blurred.
* Practice: Experiment with different aperture settings, focal lengths, and subject-to-background distances to see how they affect the blur in your images.
* Use a Lens Hood: A lens hood can help reduce flare and increase contrast, which can improve the overall clarity of your image.
* Post-Processing: While the goal is to achieve good blur in-camera, you can sometimes enhance the blur in post-processing using tools like Gaussian Blur in Photoshop, but go easy! Overdone blur looks artificial.
Example Scenario:
You want to take a portrait of a friend in a park.
1. Lens: Use an 85mm lens.
2. Aperture: Set your aperture to f/2.8 (or wider if your lens allows).
3. Subject Position: Position your friend so that they are standing a good distance away from the trees and other objects in the background (at least 10-15 feet, more if possible).
4. Your Position: Position yourself at a comfortable distance from your friend.
5. Focus: Use single-point autofocus to focus on your friend's eyes.
6. Shoot!
By following these guidelines, you'll be well on your way to creating stunning portraits with beautifully blurred backgrounds that will help your subjects stand out. Good luck!