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roccoforte

Why is anamorphic bokeh oval?

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Because the anamorphic lens projects an oval image onto your taking lens.

If you cut out some shapes on a piece of paper and put it on front of your lens, the bokeh will take that shape: http://www.diyphotography.net/diy_create_your_own_bokeh

 

The anamorphic lens is like a piece of paper with an oval cut.

It won't affect real objects, just the out of focus highlights.

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you'd expect the ovals to disappear after de-squeeze but from what i see, the lens is stretching the image more on the out of focus areas than the in focus areas.  in the same way normal bokeh is bigger the further you are away from the out of focus area.  de squeezing removes the artifacts from in focus areas but out of focus areas are distorted more.

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Yes - In my mind the oval-shaped bokeh should only be visible when you watch the footage in its pre-squeezed state. (i.e. when people are tall, and soccer balls are egg-shaped) But it remains oval even after it's been squeezed down into its rectangular aspect ratio. 

 

Logically, shouldn't the bokeh also squeeze down back into a circle?

 

But yes, I see it now; that it isn't uniformly stretched. Very interesting.

 

Thanks.

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As much as I understand about the physics of light & cameras, I think Julian is correct here. The way bokeh appears should not have anything to do with the squeezing of an anamorphic - it only has to do about another feature of an anamorphic: light from out of focus areas travelling through the ovally formed hole.

 

Here's a video from Kai at DigitalRev: http://www.youtube.com/watch?v=H5jjr_vKruU

He cuts out his own bokeh shapes from paper - even his own name is used as bokeh :)

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Something I've noticed: anamorphic bokeh has a tendency to be more oval at the edges of a frame and more true-circular near the center. Clearly, this is a result of the curvature of the glass, but what focal length / distance / diopter combination gets you consistent ovals across the frame?

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Shot with a 2/90mm at 1 metre, aperture reflections are consistent across the FOV

 

 

8360440387_576d7f05c4_b.jpg

 

 

Something I've noticed: anamorphic bokeh has a tendency to be more oval at the edges of a frame and more true-circular near the center. Clearly, this is a result of the curvature of the glass, but what focal length / distance / diopter combination gets you consistent ovals across the frame?

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Actually, the ovaline shape of anamorphic bokeh has NOTHING to do with the shape of the front element. If it did, OP is right--the ovaline shape would be reversed after the de-squeeze in post.

Instead, the shape is due to one of the weird properties of shooting anamorphic. When you shoot with, say, a 100mm 2X anamorphic lens, you get a crop factor of effectively 50mm....in the left-right axis. In the up-down axis, however, you're still shooting effectively 100 mm. Since 100mm gives bigger boken than 50mm, your bokeh will be bigger in the up-down axis than in the left-right axis. Hence the oval shape.

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