Anamorphic Widescreen Movie Lens Squeeze Ratio and Horizontal Blue Streak Bokeh Characteristics

1. The historical and physical origin of the anamorphic lens: cramming a wide screen into a narrow film

During the Hollywood film industry in the 1950s, the standard 35mm film format was an approximately square 4:3 (1.37:1 Academy Ratio). To compete with home television sets and deliver a wider field of view, 20th Century Fox developed the CinemaScope anamorphic lens system:

1. Cylindrical Optical Lens Group (Cylindrical Elements):

• Ordinary photographic lenses use symmetrical spherical or aspherical lenses, with exactly the same magnification in the horizontal and vertical directions.
• Anamorphic lenses incorporate an asymmetric cylindrical lens (similar to a horizontal cylindrical magnifying glass) in the front or rear group.

2. One-way optical squeezing:

• The lens maintains 1.0x normal magnification in the vertical direction (Y-axis);
• But in the horizontal direction (X-axis) with a fixed physical squeeze ratio (such as 2.0x), the light of the ultra-wide-angle field of view is "forcibly squeezed laterally and compressed" to half of its original width.
• The result: an ultra-wide cinematic angle of view with a lateral opening of 2.39:1, fully recorded on a conventional 4:3 area film or sensor.

3. Projection end/post-production de-squeeze:

• Stretch the picture by 2 times horizontally on the post-editing software or projector, and restore the entire picture to the magnificent 2.39:1 ultimate Hollywood wide-screen movie blockbuster!

2. Three iconic “movie-like” optical aesthetic features

It is precisely because of the physical separation of the refractive index in the horizontal and vertical directions that it gives the anamorphic lens an unparalleled and unique film texture:

1. Oval Bokeh Balls:

• The out-of-focus highlight spot of an ordinary lens is perfectly round.
• The anamorphic lens is compressed 1.5~2 times in the horizontal direction. In the bokeh area, the originally circular point light source is stretched to form an extremely elegant vertical oval light spot, which has become an iconic visual symbol of the movie screen.

2. Horizontal Streak Flares - "Science Fiction Blue Bar"):

• When car headlights, flashlights or street lights shine directly on the front lens group, the cylindrical lens group will cause strong lateral diffraction dispersion of the direct light point in the horizontal direction.
• Strips of extremely slender blue or gold horizontal flashes of light erupt across the entire screen from left to right (played to the extreme by J.J. Abrams in the science fiction blockbuster "Star Trek").

3. Perspective and Depth of Field Disconnect:

• A 50mm 2.0x anamorphic lens, which has the shallow depth of field blur and bokeh transition of a 50mm lens in the vertical direction; but has a broad field of view equivalent to a 25mm ultra-wide-angle lens in the horizontal direction! "Wide-angle field of view but with telephoto shallow blur" creates an extremely immersive sense of perspective drama.

3. Squeeze ratio specification selection matrix and sensor frame matching

4. Early in-camera monitoring and de-squeezing and post-production color grading workflow

1. In-camera/Monitor De-squeeze Display:

• If you look at the "elongated grimace" composition that is flattened laterally when shooting, the photographer will not be able to judge the proportion and focus of the composition.
• Modern cameras (such as Lumix S5 II / FX3 after firmware update) and monitors (Atomos Ninja / Shiwei) have built-in de-squeezing preview functionality.
• Enable in the menu: Distort to Squeeze Display $\to$ 1.5x / 2.0x, the viewfinder will instantly widen and flatten the picture horizontally in real time, presenting a normal true movie proportion.

2. Pixel Aspect Ratio setting of post-editing software:

• DaVinci Resolve: Right-click the clip in the media pool $\to$ and select "Clip Attributes" $\to$ Change the "Pixel Aspect Ratio" from Square to 1.5x Anamorphic or 2.0x Anamorphic. The Leonardo da Vinci timeline unfolds seamlessly and adaptively in an instant.
• Premiere Pro: Right-click the footage in the project window $\to$ "Modify" $\to$ "Interpret Footage" $\to$ Set the pixel aspect ratio to the specified magnification, and the picture will immediately be perfectly restored to a 2.39:1 movie widescreen blockbuster.