Shape of aperture

[reactan]

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]

It affects the bokeh......

 

[reactan]

so i presume the rounder the aperture, the "smoother" the bokeh??

 

[AReality]

so i presume the rounder the aperture, the "smoother" the bokeh??

yes.
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[blurblock]

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.

 

[reactan]

thanks thanks..... whats up with the 10 characters anyway? :dunno:

 

[XXX Boy]

Not only the aperture blade affects the bokeh la...besides that, the optical design is the most imp thing.

 

[showtime]

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]

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.