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In Mission Impossible III, I notice very often that bokeh is not circular, but has a shape of an oval. For example, here are two images where such bokeh is noticeable:

enter image description here

enter image description here

Does it necessarily mean that he was filmed using chroma key and the background was filmed separately and then resized using a different aspect ratio, or this is specific to the lens (maybe anamorphic lenses)? Is this made on purpose, or is just a side effect?

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It's the effect of using an anamorphic lens which squashes the image horizontally to fit a wide-screen image on conventional 35mm film. The image is then un-squashed by a similar lens on the projector when the film is screened (or by computer after the film is scanned in a digital post production environment).

Bokeh appears elliptical because the front of the lens barrel which is circular, appears as an ellipse when viewed through the back of the lens. A regular lens with an elliptical opening at the front would generate exactly the same effect.

The film's director, J.J. Abrams is well known for using anamorphic lenses for the effects they generate, which also includes unique lens flare that manifests itself as strong horizontal blue lines.

  • 1
    Ok, this was my first thought and from doing more research, I agree it is correct, but I still don't understand how it works optically. If the image is a circle getting compressed on to the film, it should be a circle when uncompressed, if it was a circle after compression, it should end up elongated in the horizontal. What am I missing that makes it so it elongates vertically, even after uncompressing the image. Is it just that something about the optics compresses the bokeh more than the in-focus image? – AJ Henderson Sep 30 '14 at 16:22
  • I tried to figure out your question myself, but I can only assume, that the stretching effect of the anamorphic lens on the bokeh is stronger than the "decompression". Film Riot did an episode on anamorphic shooting and it is quite insightful. Hopefully someone can explain, why the bokeh is stretched, because that is an interesting question. – J0hj0h Sep 30 '14 at 18:39
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    @AJHenderson The out of focus highlights are subject to two effects, they get clipped to an oval by the front of the lens barrel, which looks oval shaped when looking through the anamorphic adapter, this oval then gets squashed by the effect of the anamorphic element in the adapter. The un-squashing of the image removes the latter effect, but not the cropping, hence they appear as ovals in the final image. The cropping affect is not visible in the in focus area as each individual oval is smaller than a pixel. – Matt Grum Oct 1 '14 at 12:19
  • @J0hj0h see my response to AJ Henderson, above. – Matt Grum Oct 1 '14 at 12:19
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This is likely the result of using an anamorphic lens: http://www.red.com/learn/red-101/anamorphic-lenses

From the page:

Standard Bokeh

Standard Bokeh

Anamorphic Bokeh

Anamorphic Bokeh

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