There are two kinds of lenses that can be used in film making: spherical lenses and anamorphic lenses. Spherical lenses are the type that we all use most commonly and they pass the image to the sensor or film without affecting the aspect ratio. However anamorphic lenses distort the image, squeezing it horizontally while leaving the vertical aspect unaffected. To understand why filmmakers would want a lens to do this needs a little history lesson.
The birth of widescreen
Although a number of widescreen formats had been experimented with during the early days of cinema, the vast majority of films were shot in the standard 35mm “Academy” aspect ratio of 1.37:1 until the early 1950s. It was then that, to counter the decline in cinema audiences caused by the rise in popularity of television, film studios moved to making films in widescreen aspect ratios.
Some of the techniques used to achieve a wider aspect ratio simply involved masking the top and bottom of the 35mm film frame. However a cropped image produced in this way wastes a large proportion of each frame’s area, reducing resolution and increasing grain when it is projected.
Anamorphic lenses were developed to utilize the entire 35mm film frame, compressing the image horizontally by a factor of 2, while using the full height of the frame. When the finished film was screened at a cinema, the projector lens correspondingly unsqueezed the image back to its correct proportions. In this way, the classic 2.39:1 widescreen film aspect ratio could be obtained from film frames with an aspect ratio of 1.37:1.
The anamorphic look
While anamorphic lenses were developed to overcome the limitations of the 35mm film frame, they added a distinctive look to the images.
One of the most unique features of anamorphic images is that out of focus elements in the background produce a distinctive vertical oval bokeh. Lens flares are also visible as horizontal or vertical streaks across the frame.
In use, anamorphic lenses have an effective shallower depth of field when compared to spherical lenses, which is often considered more cinematic. To understand this effect, consider that when you are using a 50mm anamorphic lens, it has the vertical perspective of a 50mm spherical lens but, because of the compression of the image along the horizontal axis of the image, the effective horizontal focal length is that of a 25mm lens. Therefore, to achieve a similar field of vision to a 50mm spherical lens a 100mm anamorphic lens must be used with the resulting shallower depth of field.
Anamorphic lenses and digital sensors
With the advent of digital sensors, the need to use anamorphic lenses diminished. Digital video sensors typically have a wider aspect ratio than 35mm film, and so spherical lenses can be used to achieve a widescreen image with only a minimal amount of cropping.
Using a standard anamorphic lens with a 2x compression factor on a digital sensor with an aspect ratio of 16:9 will result in a final image with an overly-wide 3.55:1 aspect ratio. To achieve a 2.39:1 aspect ratio, only the central portion of the sensor is used, which can mean that the final image uses fewer pixels than would be achieved by simply masking off the top and bottom of a full width sensor. Because of this, Arri released a version of their Alexa cinema camera with a 4:3 image sensor designed specifically to produce a 2.39:1 image when paired with a 2x anamorphic lens.
There are also a number of anamorphic add-on lenses with horizontal compression ratios of 1.33:1 or 1.35:1, which are designed to work in conjunction with spherical lenses on cameras such as DSLRs with 16:9 digital sensors. However, the lower compression factor means that these adaptors produce less of the characteristic anamorphic bokeh and lens flares that filmmakers seek.
Working with anamorphic lenses
While there are anamorphic lenses or add-on lenses which can be adapted to work with most cameras, there are a number of issues to consider before planning your first anamorphic widescreen project.
Unless your camera has an option to desqueeze the image in the viewfinder or on the monitor screen, you will have to work with the horizontally compressed image, making framing and shot composition more of a challenge.
Anamorphic lenses tend to be larger and heavier than spherical lenses, which makes them less suitable for run and gun filmmaking
Anamorphic lenses tend to be larger and heavier than spherical lenses, which makes them less suitable for run and gun filmmaking. They are also likely to have slower maximum apertures, so you will need more light when filming.
Wide angle anamorphic lenses can have more distortion than spherical lenses, making it difficult to get straight verticals in your image. The lens distortion produced by anamorphic lenses can also make working with visual effects more difficult.
The extra glass elements in anamorphic lenses can affect image sharpness, though some filmmakers actively prefer the softer nature of the glass when working with 4K or higher resolution digital formats as it can reduce the overly clinical nature of the footage.
Is shooting anamorphic right for you?
Anamorphic lenses are not suitable for everyday filmmaking. However, for the right project anamorphic lenses can increase your production values and give your film a uniquely cinematic look.
Pete Tomkies is a freelance cinematographer and camera operator from Manchester, UK. He also produces and directs short films as Duck66 Films.