Wide-format film photography (Panoramic 6x17 / XPan) horizontal parallax composition and use of middle gray gradient filters

1. Film wide-format vision: the visual psychological revolution from 3:2 to 2.7:1

The standard format (3:2 or 4:3) conforms to the concentrated field of view of a single human eye, and the overlapping field of view of both eyes when human eyes are opened at the same time naturally presents a flat and grand horizontal panoramic ratio:

1. Representative classification of true wide format models:

• Hasselblad XPan (Fuji TX-1/TX-2): Using standard 135 film, you can freely switch between standard 24x36mm and horizontal double format 24x65mm (aspect ratio 2.7:1) in the same body. A single roll of 36 negatives can shoot 20~21 magnificent wide-format panoramas.
• Medium format 6x17 super wide mechanical monster (Linhof Technorama 617 / Knight 617): Using 120 film, the physical size of a single negative is astonishing 56mm $\times$ 170mm (aspect ratio 3:1), a single roll of 120 film can only shoot 4 negatives! The resolution is directly comparable to that of large format cameras.

2. Lossless optical advantages of Uncropped:

• Ordinary cameras will lose half of the pixels and photosensitive area of the frame by cropping the black bars up and down in post-processing;
• The true wide-format camera uses a super-large image circle (Image Circle) lens and covers the entire film with high-fidelity silver salt emulsion. Even if it is enlarged to a huge gallery exhibition of several meters, the details are still vivid.

2. The iron law of natural optical physics: the fourth power law of cosine ($\cos^4\theta$) and the central filter

A wide-format lens has a very large field of view (up to 90°~110°) at both ends of the lateral direction, and its edge light must overcome cruel physical and optical attenuation:

1. Cosine Fourth Law of light intensity attenuation (Cosine Fourth Law):

• The relationship between the local illumination $E$ projected on the focal plane and the light incident angle $\theta$ follows the mathematical formula:
  $$E(\theta) = E_0 \times \cos^4\theta$$
• When the field of view reaches 45° at the edge, $\cos^4(45^\circ) = (0.707)^4 = 0.25$!
• Meaning: The lens does not require any mechanical blocking, and the natural light transmission on the left and right edges of the film will automatically drop by a full 2 ​​stops (-2 EV)! If left uncorrected, the developed film will have a bright center and harsh dark tunnel vignetting on both sides.

2. The optical antidote to the Center ND Filter:

• Structural features: a reverse neutral density filter - The center of the lens is darkest (1.5 to 2 stops less light), and then smoothly gradients in concentric circles to completely transparent and colorless towards the edge.
• Working mechanism: The center filter forcibly darkens the highlight in the center of the lens by 2 stops, which physically offsets the natural 2-stop vignetting at the edges, allowing the entire 24x65mm or 6x17cm frame to obtain 100% absolutely uniform and straight exposure illumination.
• Exposure compensation: After installing the center filter, you must manually increase the exposure compensation by +1.5 EV or +2.0 EV to the right.

3. Aesthetic logic of 2.7:1 wide-format composition: horizontal narrative and film storyboard

When composing a picture in a wide frame, we must completely subvert traditional thinking to prevent the picture from falling into the embarrassment of "large areas of empty space at both ends":

1. Multi-Subject Rhythm:

• Widescreen has enough stage space to accommodate 2 or 3 subjects side by side.
• Example: Arrange a traveler sitting quietly and reading a book on the left side, and the right side echoes the train leaving the window. The middle is connected by a bench and a shadow. A single photo constitutes a complete movie storyboarding (Storyboarding).

2. Strict consideration of horizon height:

• Never just center the horizon!
• When the sky is wonderful: lower the horizon to 1/4 of the lower part of the screen, leaving a large area of white space to allow the clouds and airflow to extend horizontally;
• When the ground texture is rich: push the horizon to the top 3/4, so that the road, snowfield or desert cracks in the foreground are spread horizontally, creating a sense of oppression of the earth.

4. Precision horizontal calibration and vertical pitch control

1. Two-Axis Bubble Level:

• The lateral span of the wide frame is extremely wide. As long as the fuselage has a slight lateral tilt of 0.5 degrees, it will be magnified into an extremely obvious skew and drop at both ends of the frame.
• A high-precision two-axis double-bubble level must be inserted into the hot shoe on the top of the camera. Before shooting, the tripod leg must be repeatedly fine-tuned to ensure that the bubble is strictly locked at the center bullseye.

2. Avoid fuselage pitch causing edge buildings to tilt:

• The wide-angle lens has a huge angle of view. Once the camera is tilted up to shoot, the skyscrapers on both sides of the screen will violently collapse and deform towards the center. When shooting architectural scenery, be sure to keep the camera completely horizontal. If necessary, use a dedicated panoramic tilt-shift camera that supports vertical displacement (Shift).

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