Shape of aperture


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reactan

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Jan 2, 2004
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#1
Hi,

was just wondering how the shape of the lens aperture may affect the final product. For example, i compared 2 lens at the same f stop and focal length, one was distinctly round while the other was more angular.

Any answers?

Thanks,
AT
 

blurblock

Senior Member
May 30, 2003
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ytphoto.clubsnap.org
#5
reactan said:
so i presume the rounder the aperture, the "smoother" the bokeh??
Correct, the rounder the aperture, the rounder the boken. The angular aperture will show something like a pentagon shape bokeh.
 

XXX Boy

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Jan 11, 2004
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#7
Not only the aperture blade affects the bokeh la...besides that, the optical design is the most imp thing.
 

showtime

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May 2, 2003
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#8
the number of blades of the apperture determines the no of sides of the polygonal circles of confusion... but when wide open, the coc will appear perfectly round
 

ST1100

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Jun 18, 2003
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#9
The number of blades only affects the shape of the background blur. The optical formula also matters - the same number of blades at the same aperture can give drastically different bokeh from different lenses. Portrait lenses typically have the best bokeh - 85 and 135 primes. 50mm primes usually do not.

When stopped down, an even number of blades will produce star patterns with the same number of points as the number of blades. An odd number of blades will produce double the number of points. Eg a 50/1.8 with 5 blades produces a 10 point star, a 50/1.4 with 8 blades give 8 pointed stars. Sigma lenses which come with 9 blades give 18 pointed stars.

The COC has nothing to do with this.
 

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