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Bokeh Question


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#1 Elan Morin Tedronai

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Posted 30 September 2005 - 07:29 AM

When shooting at full aperture I have noticed that the bokeh artefacts at the edge of the frame is shaped different than the circular ones in the centre of the frame. The bokeh at the edge of the frame appeared to be a circle cut by a larger circle...

Bokeh01.jpg

Does anybody know what causes this?

Edited by Elan Morin Tedronai, 30 September 2005 - 07:33 AM.

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#2 Stephen Williams

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Posted 30 September 2005 - 08:39 AM

When shooting at full aperture I have noticed that the bokeh artefacts at the edge of the frame is shaped different than the circular ones in the centre of the frame. The bokeh at the edge of the frame appeared to be a circle cut by a larger circle...

Bokeh01.jpg

Does anybody know what causes this?

<{POST_SNAPBACK}>



Hi,

I think it's vignetting.

Stephen
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#3 Kim Sargenius

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Posted 30 September 2005 - 09:48 AM

Hi,

I think it's vignetting.

Stephen

<{POST_SNAPBACK}>



Sort of - it's called "Cat's Eye Bokeh" and is a form of mechanical vignetting you could say.

It's caused by either the front or rear element being a bit too small and so it will cut the bokeh much in the way that a front matte can do on long lenses.

Check out Paul Van Walreewebsite for great primers on this and a lot of other optical phenomena.



HTH

Kim Sargenius
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#4 Elan Morin Tedronai

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Posted 30 September 2005 - 11:44 AM

Thanks a lot! Had the feeling it was something like that...
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