Exposure balance of city night scene in Blues Moment and traffic starburst bracketing exposure technique

1. Blue Hour physical lighting evolution and optimal time window

Many novice photographers think that when shooting city night scenes, they have to wait until the sky is completely dark late at night. As a result, they end up shooting low-quality night scenes with "a completely black sky and dazzling white and overexposed building lights." The golden hour for high-quality nightscapes only occurs during the blues hours after sunset:

1. Conversion mechanism of cold and warm light in the sky:

• When the sun sinks below the horizon at an angle of -4° to -8°, the ozone layer in the atmosphere strongly absorbs long-wave red light, allowing only short-wave high-frequency dark blue scattered light to penetrate and illuminate the earth. The entire sky appears extremely deep and highly saturated sapphire blue and azure.

2. The golden balance point of 1:1 ratio of natural light to artificial light:

• At this time, the interior office lights, street lights and car lights of city buildings have just turned on.
• What is extremely rare is that the remaining dark blue diffuse light brightness in the sky happens to be in almost the same dynamic range range (light ratio about 1:1 to 1:2) as the surface brightness of the city's artificial warm yellow lights!
• The camera can simultaneously capture the transparent layered blue tones of the sky and the soft warm golden light inside the building with a single exposure. The cold and warm colors of the two complement each other and create a magnificent picture.

3. Window time only 15 to 25 minutes:

• The blues moment is extremely short, usually only lasting about 20 minutes a day. You must get on a tripod 30 minutes in advance to complete the framing and composition, and wait for the moment when the brightness of the sky light falls to align with the ground lamp and take decisive continuous shots.

2. Rail drawing long exposure and small aperture starburst physical adjustment

Urban overpasses and lanes are the life arteries of night scenes. Through slow doors, the traffic flow is transformed into golden and red light strips:

1. Front lights and rear lights have color temperature distinctions:

• Oncoming traffic displays a dazzling white/light yellow band of light (headlights);
• Pulling away from traffic presents a deep, saturated bright red tail light strip.
• When composing the picture, it is recommended that the driveway form a beautiful "S" shape or diagonal line, with red and white light flowing throughout the entire city hinterland.

2. Aperture setting and lens Sunstar blade number algorithm:

• Stop down the aperture to f/8 ~ f/13 (such as f/11).
• The small aperture can diffract the point light source of the street lamp into a sharp and dazzling radial star.
• Rules for the number of starburst lines: When the number of aperture blades of the lens is an even number (such as 8 blades), an equal number of 8 starbursts will be emitted; when the number of aperture blades is an odd number (such as 9 blades), the interference of the starbursts will be doubled, and a dense and gorgeous 18 starbursts will be emitted.

3. Shutter time calculation (10s ~ 30s):

• In order to make the rails smooth and continuous without any broken ends or tails, the shutter time must be long enough (at least 15 seconds to 30 seconds) to allow the traffic to completely pass from one end of the overpass to out of sight.

Three, three automatic exposure bracketing (AEB) large light ratio synthesis specifications

Even during blues moments, direct close-ups of LED signs and dark architectural shadows can exceed the dynamic range limits of a single RAW. Auto Exposure Bracketing must be used:

1. Body parameter setting:

• ISO is fixed at ISO 100, the native lowest sensitivity, eliminating any digital noise;
• The drive mode is set to AEB 3-stop continuous shooting (-2 EV, 0 EV, +2 EV), and the step size is set to 2EV.
• Turn on 2-second timer Selfie or use a wireless shutter release to completely avoid the slight shaking of the body caused by pressing the shutter with your finger.

2. Grade division of three images:

• -2 EV Dark shot: The shutter is about 2 seconds, recording the core outline details of the neon sign text of the building and the street lights without being exposed.
• 0 EV Baseline shot: The shutter is about 8 seconds, showing the best sapphire blue level of the sky and the gray outline of the overall city night scene.
• +2 EV Bright shot: The shutter is opened for about 30 seconds to lengthen the complete drawing track of the car rail and completely wash out the delicate material of the glass fiber reinforced plastic structure in the dark part of the building.

3. Lightroom/Photoshop 32-bit HDR compositing:

• Select three DNG/RAW, right-click and select "Photo Merge $\to$ HDR".
• Check "Auto Align" and "Micro Decolorization" to generate a 32-bit ultra-high dynamic range DNG file.
• In high dynamic files, the highlights (Highlight -50) and the shadows (Shadow +30) are simultaneously restored, making the entire night scene dazzling and free of noise and overexposure.

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