Dunkirk and the puzzling world of IMAX — a guide

The new Christopher Nolan movie is premiering in the US on the 21st July, and there is a lot of hype. Based on Nolan’s track record with the movies he’s directed, I would advise you go and see it in a theatre if you want a truly amazing experience.

However, there have been a lot of words thrown around regarding this movie such as “IMAX”, “lieMAX”, “70mm”, “35mm”, “4K”, “2K”, “laser” etc. Here I will explain everything you need to know so you can watch the movie in the best format for you.

Firstly, in a theatre, a movie can be shown in two categories of formats:

  1. Digital
  2. Film

And it can be shown in special screening types, like IMAX.


IMAX is a special type of screening which is specifically approved on a theatre-by-theatre basis by the IMAX corporation. The objective of it is to immerse the audience more compared to regular theatres, which is done by increasing picture quality, screen size and sound quality.

There are two terms typically used by movie fanatics to describe individual IMAX theatres, “true” IMAX and “lieMAX”.

A “true” IMAX screen has a 1.43:1 aspect ratio, which makes for a very tall image that fills up the entirety of the screen, resulting in a more immersive experience. A “true” IMAX shows movies available in 15/70mm IMAX film in that format (e.g. Dunkirk) but most other movies will likely be shown in digital due to the lack of movies available on film.

In 2008, IMAX started allowing multiplex theatres to have an IMAX auditorium but with less rigorous standards. The issue is that these generally don’t have anywhere near the same experience as a “true” IMAX and therefore are referred to as “lieMAX”. This is due to a much smaller screen at a normal 1.9:1 aspect ratio, a 2K (sometimes 4K) digital projection system for all movies and a sub-par sound system compared to their “true” counterparts.

Only a handful of IMAXs are regarded as “true” out of all of them (about 1/10, but some “true” IMAXs are still in multiplex theatres), so check with the theatre if the movie is shown in a 1.43:1 aspect ratio and what type of projection system they use. If, for Dunkirk, they say that it is shown in a 1.43:1 aspect ratio and it is shown on 15/70mm IMAX film, then it is a “true” IMAX.


Without getting too technical, the vast majority of theatres show movies in a digital format since it is less expensive and much easier to show compared to film. Unless a theatre specifies any type of special format e.g. “70mm film” for a screening, assume it will be in digital.

When shown in digital, it will typical be in one of two resolutions: 2K or 4K. 2K has been the standard for quite a while now, but 4K has started to roll out in the last few years. The difference is that the picture on a 4K projection will be much sharper and detailed compared to a 2K projection.

To tell the difference between 2K and 4K screenings, assume the screening will be in 2K unless it is specified to be shown in 4K. For IMAX, IMAX “xenon” or “digital” is a 2K projection whilst IMAX “with laser” is a 4K projection using lasers instead of a xenon lamp.

Two IMAX “digital” projectors


Film is a physical medium where light is projected onto cells which produces an image. Depending on how a movie was shot and produced, a movie shown in film in a theatre could either be a digital master (digitally shot then printed on film) or it could have been shot in film which will be the best experience.

When talking about film, there are really only 3 terms you need to know:

  1. 35mm
  2. 70mm
  3. 15/70mm IMAX

35mm is the standard type of film for movies that use film and is still commonly used in Hollywood. It’s comparable to 4K digital in terms of resolution, so it’s not that big of a deal when compared to other types of film. The big difference between digital and film is 70mm and 15/70mm IMAX.

70mm film (also known as 5/70mm) is effectively just a larger version of 35mm, the difference is that due to the increased size, there is a lot more detail captured (higher resolution) which results in a stunning picture. 15/70mm IMAX film (also known as 70mm IMAX) is like 70mm film, but it is shot horizontally compared to vertically so the image is much taller which results in a much more immersive experience. The “15” just refers to the number of sprockets used for each frame

Since approximately 75% of Dunkirk was filmed on 15/70mm IMAX film (with the rest being on regular 70mm film), it will look absolutely amazing when actually watched in that format in the theatre. Do note that very few movies are shot in 70mm, so check if the movie you’re seeing was before paying the extra to see it in that format at the theatre.

Relative frame sizes of the different types of film


If you want the best experience when watching Dunkirk, see it in 15/70mm IMAX. It will look the best visually, sound the best and will be how Christopher Nolan wanted you to see it: as immersive as possible to put you in the shoes of the soldiers in Dunkirk.

If you can’t do that, then 70mm isn’t much of a downgrade since you’re only chopping off some of the top and bottom but due to the lack of IMAX in some theatres, the sound may not be as good and the screen size may be considerably smaller.

35mm is a bigger downgrade from 70mm, but it will still look great and will still have the “film look” which Christopher Nolan praises heavily. From 35mm to 4K isn’t a huge difference, but you won’t get the same “film look”. 4K to 2K is a big change when on such a large screen, but it isn’t as if 2K will look bad — it just won’t look as good as the other formats.

A visual representation of the different formats available