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03-24-2012, 12:53 AM   #1
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Rounded aperture blades, benefits?

Hi,

I was wondering what the difference is between rounded and non-rounded aperture blades and how will it work out in the photo?

Thanks!

03-24-2012, 01:00 AM   #2
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Short version-
When stopping down, the rounded aperture blades will keep the out of focus highlight's a more rounded shape than a lens with straight blades, which will have polygons or octagons etc... depending on how many blades it has
03-24-2012, 01:27 AM   #3
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For example, in this picture, you can see the non rounded shape of the aperture in the background:

03-24-2012, 02:31 AM   #4
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For examples of round aperture look at this thread. These preset lenses often have large numbers of aperture blades making for circular oof highlights. Post no.10 has one example.

03-24-2012, 03:56 AM   #5
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What they said above. I own the DA *55 and D FA 100mm WR, both of which have specifically rounded blades, which tends to keep the bokeh circular, rather polygonal.

DA *55



D FA 100 mm WR



Sigma 30mm



The Sigma clearly has different quality to out of focus areas.
03-24-2012, 04:46 AM   #6
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Is the first time i see the DA*55 that soft, the background blur is normally a lot more defined.
03-24-2012, 04:49 AM   #7
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https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/86625-lens-buy...ant-macro.html

Shows clearly the difference between the DFA100 and the DFA100WR
03-24-2012, 06:30 AM   #8
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The other thing that really well sculpted blades, or very high blade count preset lenses have is the reduction in defecation artifacts at the intersection of the blades. With flat blades these artifacts caus the starbursts when stopped down and shooting into bright point sources of lights. Lenses with round at all aperture designs largely avoid these artifacts.

As others have said, the lack of sharp shaped tends to produce better softer bokeh, but I also find that the easiest way to notice this is in areas that are only marginally out of focus. Round aperture lenses due to the softer bokeh, seem to produce better separation of foreground and background. I noticed this when testing a tele lentar pest 135 against an SMC tak 135. At every aperture the preset lens had more depth or separation of foreground and background.

03-24-2012, 06:55 AM   #9
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QuoteOriginally posted by Lowell Goudge Quote
As others have said, the lack of sharp shaped tends to produce better softer bokeh
That's a common misbelieve.
It's true that 5 aperture blade produce softer bokeh then 3 bladed one but we are talking about such low numbers now.
Just compare the photos of the DFA 100 versions in the link above they both have 8 blades but the WR version is rounded.
As you can see the light distribution in the blurred highlights is the same and that's what bokeh is all about as you can see the blurred background of these lenses are the same as long as you don't see the highlights.
It's the lens elements that for the most part shape the bokeh.


You can also compare the FA50 and DA*55, both are slightly different but they similar bokeh but the DA*55 has rounded blades.

It's great a lens has rounded blades but it's not a deal breaker for me if it doesn't.
03-25-2012, 12:49 PM   #10
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I was out today and has taken that a couple of pictures to nail it down:

Lens stop down with no rounded blades



Lens wide open (similar behavior as with rounded blades)

03-26-2012, 06:22 AM   #11
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QuoteOriginally posted by Anvh Quote
That's a common misbelieve.
It's true that 5 aperture blade produce softer bokeh then 3 bladed one but we are talking about such low numbers now.
Just compare the photos of the DFA 100 versions in the link above they both have 8 blades but the WR version is rounded.
As you can see the light distribution in the blurred highlights is the same and that's what bokeh is all about as you can see the blurred background of these lenses are the same as long as you don't see the highlights.
It's the lens elements that for the most part shape the bokeh.


You can also compare the FA50 and DA*55, both are slightly different but they similar bokeh but the DA*55 has rounded blades.

It's great a lens has rounded blades but it's not a deal breaker for me if it doesn't.
I think you need to consider 2 separate points in the issue sculpted vs non sculpted blades and round apertures, first, when many lenses have 5 or 6 blades non sculpted blades, comparing them to a lens with 8 or more baldes, sculpted or not the bokeh is usually better in the lens with higher blade counts, but I agree, there is a limit to that.

the other point, and this is not blade related but lens design related, is how sharp and defined the edge of the OOF region is. Someone a while back was doing work in defining the light distribution through out the OOF region. some lenses had hard edged OOF detail with uniform illumination through out the detail, others had softer edges and the edges were not as bright as the center, this led to a smoother blending of the OOF detail. Many older presets have this behavior, and it really does lead to better separation of foreground and background, especially if you compare, for example, a 6 bladeed SMC Tak 135/3.5 to a 14 blade Preset 135.
03-26-2012, 02:45 PM   #12
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QuoteOriginally posted by Lowell Goudge Quote
in defecation artifacts
LOL - think you meant diffraction artifacts - gave me pause for thought - maybe you had just a little more than dust in your lens.
03-26-2012, 05:05 PM   #13
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QuoteOriginally posted by Arjay Bee Quote
LOL - think you meant diffraction artifacts - gave me pause for thought - maybe you had just a little more than dust in your lens.
Maybe that's why my pics always look like shit.
01-17-2017, 07:53 AM   #14
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Ahoy!

I think this website both shows and explains the differences so well that even I can understand it. I'm sure this will be of use to all shooters. You can read about it and view images on this website using a Sigma AF 500/4 telephoto lens just to cover focal range and whether any particular lens type produces images differently.

I appreciate this is an old thread, but the question like many others, will always be asked and it's therefore as relevant today as it was before and will be in the future, so no bad thing to cover the subject from an older thread IMO.
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