1. Aperture (f-number):
* The Key Factor: Aperture is the size of the opening in your lens that lets light pass through. It's measured in f-numbers (e.g., f/1.8, f/2.8, f/4, f/5.6).
* Wider Aperture = More Blur: A wider aperture (smaller f-number like f/1.8 or f/2.8) creates a shallower depth of field, meaning only a small portion of the image will be in focus, resulting in a blurred background.
* Think of it like this: Imagine looking through a tiny pinhole versus looking through a wide tunnel. The pinhole makes everything seem more in focus, while the wide tunnel blurs the edges.
2. Focal Length:
* Longer Focal Length = More Blur: Using a longer focal length (e.g., 85mm, 135mm, 200mm) compresses the background, making it appear closer and exaggerating the blur.
* Why it works: Longer lenses magnify the subject and background equally, but the increased magnification makes the background blur more noticeable.
* Ideal for Portraits: 85mm is often considered a classic portrait focal length.
3. Subject-to-Background Distance:
* Greater Distance = More Blur: The farther your subject is from the background, the more blurred the background will appear.
* How to achieve it: Position your subject far away from any walls, trees, or other objects in the background. If you can, find an open field or park.
4. Sensor Size (Camera Body):
* Larger Sensor = More Blur (Generally): Cameras with larger sensors (like full-frame) generally have a shallower depth of field compared to cameras with smaller sensors (like APS-C or Micro Four Thirds) at the same aperture and focal length.
* Why: Larger sensors allow you to use wider apertures without the depth of field becoming too shallow for your subject.
* Crop Factor: If you're using an APS-C or Micro Four Thirds camera, you'll need to consider the crop factor, which effectively multiplies the focal length of your lens. To get the same blur as a full-frame camera, you might need to use a wider aperture or a longer lens (after accounting for the crop factor).
5. Distance to Subject:
* Closer to Subject = More Blur: The closer you are to your subject, the shallower the depth of field, and the more blurred the background will be.
* Balancing Act: While getting close helps, you want to find the right balance to avoid distortion, especially with wider lenses.
Practical Tips & Steps:
1. Choose the Right Lens:
* Prioritize lenses with wide maximum apertures (f/1.2, f/1.4, f/1.8, f/2.8). These are often called "fast" lenses.
* Consider portrait-specific lenses like 50mm, 85mm, or 135mm.
2. Set Your Camera to Aperture Priority (Av or A) Mode:
* This allows you to control the aperture while the camera automatically adjusts the shutter speed.
* Alternatively, you can shoot in Manual mode and control both aperture and shutter speed.
3. Select a Wide Aperture:
* Start with the widest aperture your lens allows (e.g., f/1.8, f/2.8).
* Adjust as needed. If the background isn't blurred enough, try a wider aperture if your lens allows. If too much of your subject is out of focus, narrow the aperture slightly.
4. Position Your Subject:
* Move your subject as far away from the background as possible.
* Adjust your distance to the subject to find a pleasing composition and level of blur.
5. Focus Accurately:
* Use single-point autofocus and ensure your focus point is on the subject's eyes (usually the nearest eye).
* If using continuous autofocus (AF-C or AI Servo), keep the focus point on the eye.
6. Check Your Results:
* Take a test shot and review the image on your camera's LCD screen.
* Zoom in to check sharpness on the subject's eyes and the level of background blur.
* Adjust your settings as needed.
7. Consider Lens Quality: The quality of your lens also contributes to the aesthetic of the bokeh. Higher quality lenses often produce smoother, more pleasing bokeh.
Example Scenario:
* Camera: Full-frame camera
* Lens: 85mm f/1.8
* Settings: Aperture Priority mode, f/1.8, ISO 100 (adjust as needed for proper exposure)
* Subject Placement: Position your subject 10 feet away from a background of trees.
* Focus: Focus on the subject's eyes.
Troubleshooting:
* Not enough blur?
* Widen the aperture (lower the f-number).
* Move your subject further from the background.
* Get closer to your subject (carefully, to avoid distortion).
* Use a longer focal length lens.
* Too much blur?
* Narrow the aperture (raise the f-number).
* Move your subject closer to the background.
* Move further away from your subject.
* Use a shorter focal length lens.
* Subject not sharp?
* Ensure accurate focus on the eyes.
* Check your shutter speed is fast enough to avoid motion blur (especially in low light).
* Make sure you are not shooting at too wide of an aperture where your subject is completely out of the depth of field.
* Harsh Bokeh Sometimes the out-of-focus areas are distracting or unpleasant. This is often referred to as "busy" or "harsh" bokeh. Experiment with different backgrounds and lens combinations to find what looks best to you.
Practice is key! Experiment with different aperture settings, focal lengths, and subject-to-background distances to understand how they affect the background blur in your portraits. Have fun!