Balls Cut Off - EF 85mm f/1.4L

fishy wishy said:

Best thread title in a long time.

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fishy wishy said:

Best thread title in a long time.

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fishy wishy said:

Best thread title in a long time.

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ed rader said:

world is finished.

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Dave said:

fishy wishy said:

Best thread title in a long time.

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Am I the only one who thought it was in reference to the dog?

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Marco Nero said:

The 85mm f/1.2L II USM cut off some balls this week for me as well. The stars in the sky ended up getting cat-eyed and clipped. Not sure what anyone can do to reduce this since this is a physics issue. Stopping down the lens eliminated the effect.

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Mechanical Vignetting...
The cause is actually surprisingly simple: As you know, the shape of bokeh balls is produced by the shape of the aperture. A round aperture produces round bokeh balls if there's enough aperture blades and a smaller aperture produces smaller balls because the aperture is much smaller. If you want heart-shaped bokeh balls you cut out a heart shape from a piece of paper and then stick the sheet with the heart-shaped hole in front of your lens.
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In the photograph above I've captured some clipped balls (stars in the night sky) but see how the camera shown in the image above is tilted away from this lens? Its visible optics are now forming an ellipse from this angle... just like a cat's eye. So light entering that lens from this angle or similar is just going to produce a cat-eye shaped bokeh ball. The additional "clipping" is caused by a secondary crop which is caused by the shape of the rectangular inner area of the lens towards the sensor.
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This is more likely to happen with "wider" medium-length lenses than "longer lenses" since it's the light entering from an oblique angle that causes the cat-eye effect and the "clipping" of these elipses will be the result of internal clipping. But it's unavoidable and I whilst round bokeh balls are desirable to some, it doesn't mean there's a problem with the lens. It just means that the light isn't "on axis" as it passes through the lens to reach the sensor. The effect can be reduced by stopping down the lens. It is most prominent with wide apertures and mid-range bright (fast) apertures.
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