Night scene portrait light spot (Bokeh) carving: background diffusion circle size control, foreground light spot blocking and small colorful light string play

1. The optical formation mechanism of large light spots in night scenes: point light source and out-of-focus dispersion

The beautiful light spot is not a post-processing filter, but the physical reshaping of the point light source outside the hyperfocal distance:

1. Physical defocus of point light source:

• The luminous point of distant car taillights, street lights or Christmas lights is extremely small and is equivalent to a point light source in geometric optics;
• When the focus point is accurately focused on a human face 1.5 meters in front of you, the parallel light emitted by the point light source at infinity cannot converge to a point on the sensor, but diverges to form a circular spot whose cross-section is exactly the same as the shape of the aperture;

2. Regulation rules for spot size:

• The larger the light spot, the more needs to be met: ① The longer the focal length of the lens (85mm/135mm); ② The aperture is opened to the maximum (f/1.2~f/1.8); ③ The farther the character is from the distant light source (for example, the background light source is 50 meters away).

2. Miniature Light String (Fairy Lights) Foreground Spot Operation Manual

Practical techniques that are extremely cheap but can bring a movie-like texture worth thousands of dollars:

1. Warm white light micro button battery copper wire lantern (must have props):

• Prepare a string of 2~3 meters long thin copper wire LED warm yellow small light strings;

2. Wrapping and blurring in front of the lens:

• Wrap one end of the light string casually around the edge of the hood in front of the lens, leaving the middle field of view without blocking the person's face;
• Core Physics Miracle: A small light bulb that is only 2~5 cm away from the lens lens will be extremely blurred in the picture into a huge translucent golden light ball with a diameter of several centimeters because it is extremely far from the focus plane!
• These spots of light float in front of the model's eyes and around her body, creating a dream-like feeling.

3. Exposure balance red line for night scene portraits: it is strictly forbidden to have dark faces or overexposed backgrounds

1. The face must have an independent soft light source:

• If you rely on weak street lights to shoot night scenes, the face will inevitably be sallow or underexposed; you must hold a small portable tablet soft fill light (color temperature adjusted to 3200K~4000K) to slightly illuminate the face at 45 degrees from the side and front;

2. Shutter control of background light spots:

• The camera uses M mode, opens the aperture to the maximum locking spot size, slows the shutter speed to 1/60s to ensure that the distant background neon lights and traffic can be fully exposed, and sets the ISO to 800~1600.

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