An anamorphic lens is a special tool that affects how the image is projected onto the camera sensor. They were originally created to allow a wider aspect ratio to be adapted to standard film images, but since then, cinematographers have become accustomed to their unique appearance. So what are the main considerations for using anamorphic lenses in the digital age?
Two types of lenses are usually used in production: spherical and anamorphic lenses. Unless otherwise specified, spherical surfaces are more common and are assumed lens types. The spherical lens projects the image onto the sensor without affecting its aspect ratio. So, what is an anamorphic lens? An anamorphic lens will project a version of the image compressed along a longer dimension (usually twice). Therefore, anamorphic lenses need to be subsequently stretched in post-production or projectors for correct display.
The original design purpose of the anamorphic lens was to make the wide-format image take full advantage of the film area of the standard 35mm format. Otherwise, a wide image will leave the top and bottom of the frame unused and need to be cropped out using a mask in the projector. Therefore, anamorphic lenses improve image quality by increasing vertical resolution and reducing the appearance of grain. For example, using a standard spherical lens to capture a 2.40:1 image on 35mm film only takes up 50% of the area of each frame. With an anamorphic screen, 100% of the frame area contributes to the final image.
Anamorphic lenses often have very different uses from digital lenses. Since most digital sensors have a higher aspect ratio than 35mm film, spherical lenses can usually record wide enough images with little cropping. The use of an anamorphic lens usually produces an unnecessarily high aspect ratio, in which case the side of the image is not used and the horizontal resolution will be reduced. Therefore, an anamorphic lens can only improve image quality when an aspect ratio higher than that captured by a digital sensor is required. However, unless the required aspect ratio is very large, a vertically cropped image will usually retain more pixels.
For example, the resolution of the full format RED DRAGON is 6144x3160, and its aspect ratio is 1.94:1. To generate a 2.40:1 wide image, you can use the "6K WS" setting to crop the top and bottom of the frame, in this case, 81% of the pixels will be retained. Another method is to use a 2X anamorphic lens. In this case, you need to crop both sides of the picture, and only 61% of the pixels are retained. People may use the less common 1.3X anamorphic lens and retain 95% of the pixels, but the effect may be too subtle to justify any added cost or complexity.