The next time you go to the cinema, watch the screen carefully after all the commercials1 have finished. Usually the curtains will draw back, and the top and bottom borders will move in to create a wider, shorter screen. The new size of the screen is the film's 'Aspect Ratio'.
In the 1950s, with the arrival of television, many filmmakers began to experiment with the size and shape of the recorded image on the screen. This was to enable them to compete with the mass medium of TV and provide cinemagoers with something TV could not.
What is 'Aspect Ratio'?
Put simply, aspect ratio is the size and shape of the image on a screen or projection; the proportion of its width compared to its height. Until recently, standard TV was modelled on a 4:3 aspect ratio, which means that if you had a screen 4 metres in width, it would be 3 metres high, hence 4:3. In film, aspect ratios become more and more complex depending on types of film stock used, budgetary requirements, post production issues, artistic effect, final delivery medium (TV, Cinema, DVD) and other issues. It is for this reason you will see figures such as 1.66:1 or 2.35:2 - the ratios are reduced down to their lowest common value, otherwise we would see silly ratios like 8.3:5 (which is actually the same as 1.66:1).
16Mm And 35Mm - What Does That Mean?
These are the two most common film formats or film stock used in film production today, and until the recent advent of high quality digital cameras (High Definition, not DV), were the staple diet of any professional filmmaker. 16mm and 35mm are the two types of film stock used. 35mm film is exactly the same sort of film you put in the back of a stills camera (or maybe your mum and dad did, depending how old you are), and is the measurement of the width of the film. 16mm is therefore smaller, or narrower, than 35mm.
However, instead of having a small roll capable of taking up to 36 still images, film producers buy film stock per foot. 400 ft of film, a standard length of film, can take up to 14,400 still images (frames), or approximately 10 - 11 minutes of film footage, as long as the camera you are using is filming at 24 frames per second2, ie, for every one second of time it takes 24 still pictures or frames.
There are many reasons to use different types of film stock. Some are technical, but often the reason for a production to use a certain type of film stock over another is either budgetary or creative, and sometimes both. In simple terms, the larger the film, the more expensive the production (not always true), and so producers on limited budgets often use narrower, smaller stock, from super 16mm and 16mm to super 8mm or 8mm3.
On smaller stock, the surface area on which a picture is stored is smaller, and therefore fewer light sensitive grains to develop a picture. The greater the surface area the better quality a picture will be4. Compared to 35mm, 16mm is therefore lesser quality, and 8mm less again. Furthermore, the developing chemicals and grain on some smaller stock is often less able to deal with fluctuating light conditions, and will react far less favourably than bigger stock. This is also related to the film's speed (ISO Rating). Smaller film stock generally has slower film speeds, and the faster the film stock the more capable it is of dealing with difficult lighting5 conditions.
However, not all directors like this 'perfect' solution, and some will deliberately use lesser stock to produce particular visual effects. One prolific user is the director Oliver Stone, and many music video directors make use of these formats for creative effect.
Film Formats and aspect ratios
This entry ignores the 8mm and Super 8mm, 70mm and 'IMAX' (70mm 15 perf6) size film stocks and unusual size film from past formats. It also only explains aspect ratios for film formats only, not digital or TV.
A lot of TV nowadays utilises new technology such as High Definition cameras to film dramas (News and ENG - Electronic News Gathering - tend towards the lower end of technology, such as DV and DVCam formats). The progression towards tapeless and solid state formats from the old Digi Beta and Beta SP to the record to disc format (such as the Sony XDCam) and the developments of direct to hard disk recording being tested by the likes of Arri Media, Panasonic and Panavision are beginning to impact on the age-old filmmaking process. All these new and future formats can record and deliver a variety of aspect ratios on spec, constructed digitally in post production from the original recording without the lengthy process of developing film and transferring it to a digital medium for editing.
The format and 'aspect ratio' that a film is shot in is usually agreed by the director and director of photography prior to any physical production. Below are some examples of different 'gate' formats. The 'gate' is the window between the lens and the film or recording medium (eg, digital tape, 16mm film, DVD), which can be altered, depending on the camera and format, to reflect the aspect ratios described below.
Note: The groundglass may or may not be the same as the gate eg, a 1.66 hard mask may be used when shooting in a 1.85:1 aspect ratio to mask off the outer area so as not to get the infamous 'boom in shot' when the film is projected in theatres. This happens because the cinemas have the ability to crop the film differently on the projector. The 'groundglass' is exactly what it says it is; a piece of ground glass shaped to fit into the camera. Depending on its size, shape, colour and usage a groundglass can be utilised for many purposes, from 'masking' off an area of the frame or picture to colour and light filters, such as neutral density filters, or ND for short.
Standard 16mm or 1.37:1 (Academy)7
This gate format allows an area down the non-perforated edge of the film to be left blank so as to provide an area for an optical sound track to be added later.
Super 16mm or 1.66:1
Uses the sound track area mentioned above to increase the width of frame therefore giving a larger negative area and less apparent graininess.
1.37: 1 (Academy)
This is a 'standard open gate' (although it will never be referred to in this way). This allows all standard formats (excluding anamorphic) to be used whilst leaving an area for an optical soundtrack.
As mentioned above, this gate is usually used in conjunction with a 1.85:1 groundglass so that the top and bottom of the negative are masked off. This still allows some re-alignment of the image in post production, but means that it is the Director and not the cinema that dictates the projection aspect ratio of the film.
1.78:1 or 16:9 is a format developed for TV. As a result this gate is never used. Television productions usually go to telecine8 and will usually shoot with an open gate so they can crop the frame in post production.
This is rarely used although it gives the Director ultimate control of the projected aspect ratio, as it will be seen in cinemas the way it was shot on location. The down side to this is there is very little room for error - no realignment is possible in post.
The anamorphic9 format uses special lenses that squeeze a picture twice the width of the gate into the gate area. A similar lens is used to un-squeeze the picture when it is projected. This format has a very distinct look about it, and the image also has a higher resolution than its Super 35mm rival, as the whole of the negative area is being used, therefore reducing apparent grain.
1.33:1 (open gate)
This is an open gate and will be referred to as such within the industry. This allows the maximum amount of information to be recorded on the negative because, as with Super 16mm, it uses up the area reserved for optical soundtrack. In the case of a theatrical release the image would have to be optically reduced to a standard format print to open up the area for the sound track to be printed. Again, with the extra area gained comes the reduced apparent grain.
As described in the standard section above, but for use with Super 35mm groundglass (ie, S1.85)
As described in the standard section, but for use with Super 35mm groundglasses
As described in the standard section but for use with Super 35mm ground glasses. Could be used for theatrical release if the production was going via a digital intermediate (scanned then laser recorded to film) to print rather than by the traditional optical printing methods. Again, re-alignment issues may arise.
Unlike the anamorphic version above, this gate crops the negative. This image is later optically converted (squeezed) to an anamorphic print. The benefits of this are sharper images with less edge distortion than anamorphic lenses, and the ability to shoot in lower light conditions, as normal lenses are 'faster' (let more light through) than anamorphic lenses.