With modern cameras, it’s much easier to achieve a deep depth of field, but there’s still something to be said about the split focus diopter shots that we saw in early film.
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What is a Split Focus Diopter
A split focus diopter is a filter that you can add to your lens to create a deep depth of field (AKA when a large area is in focus). It’s a glass filter with two thicknesses that creates a special effect of two different depth of fields.
Split Diopter Filter from Prism Lens FX
But this differs from using a small aperture in that you still have areas that are out of focus. So it’s a rather unique shot that catches the eye. Here’s an example from the movie The Untouchables:
Notice that both subjects are completely in focus, yet there are still areas around them that are out of focus.
Here’s another example in the movie Reservoir Dogs where the effect is clear:
The effect is quite pronounced in the above shot, perhaps even a little distracting for some viewers. In any case, Quentin Tarantino is known for bending and breaking rules. His bold decisions have led to Academy Awards and a number of financially successful films.
Again, it’s use case in today’s film is fairly limited as modern cameras are able to achieve a deep depth of field. The effect is fairly easy to replicate in-post as well. But before digital cameras, filmmakers had to achieve this with a split focus diopter lens (as seen above). Michael Maven explains this in his video “What is a split diopter? How filmmakers cheated depth of field for decades”:
What are modern use cases for a split focus diopter?
Again, the most popular use case is from Quentin Tarantino, who has a love for film noir style cinema. He’s used a split diopter early on in his career and more recently in films like 2015’s The Hateful Eight.
Since the effect isn’t functionally important nowadays, a modern use case is a stylistic choice.
If evident, a split diopter can look quite jarring on screen. It can help create tension in a scene and leave the audience feeling uneasy.
2019’s Toy Story 4 uses a split diopter to this effect — and becomes the first animated film to incorporate the focus style in the process.
How Can I Achieve This Shot?
The easiest way to achieve this effect is to purchase a lens. Although, good quality split focus diopters are becoming rare, and therefore, expensive! Many filmmakers want to create this effect without having to buy a filter.
We have a couple options to get a similar effect but there are still characteristics of the filter that are difficult to replicate in-camera, or in-post.
The first of which is to use a deep depth of field (eg. f/22) on a smaller sensor (eg. Micro Four Thirds). The problem is that you would have to add a lot more light to compensate for the small aperture. It’s also quite known that after about f/11 on most lenses, sharpness drops significantly.
It also wouldn’t be a true split focus diopter shot because everything would be in-focus. Whereas with a split focus diopter, you will have a plane out of focus that separates the two fields.
You could also achieve this shot in-post as it’s a relatively simple task for any modern video editor. Shooting from a locked down camera, simply do two takes and combine the footage in post to create the desired effect. Make sure your subjects don’t get too close together to simplify the editing process.
Like a dolly zoom, or the dutch angle, a split focus diopter shot should be used selectively. It should have intention, and a reason why it would be a better option then a shot with a deep depth of field.
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