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03-30-2010, 03:25 PM   #1
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Why does the number of aperture blades matter?

I was looking around at one of the threads here about lenses with 15 aperture blades or more and began wondering how much that matters. Does it affect image quality or just bokeh?

03-30-2010, 03:34 PM   #2
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Since the two are closely related, I guess you could say both. The more blades, the smoother the bokeh, typically. Now that doesn't always mean 'better'- but you'll find that most higher-end lenses have at least 8 blades, and that's now without reason.

Not the best comparison, but have a look at the bokeh:
(6)


(9)

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03-30-2010, 03:37 PM   #3
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Thanks for the quick response, i can see why that is now.
03-30-2010, 03:40 PM   #4
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The # of blades determines how the shape of bokeh looks like when stopped down, but whether the bokeh would be smooth or donut like is determined by the actual optics.

03-30-2010, 04:16 PM   #5
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There was An intresting thread last week (or two?) where the OP was looking at light fall off across the OOF circle that mmakes up A significant portion of bokeh.

This showed the difference between mAny lenses in the harshness of bokeh

it did not address the impact of round vs octagonal or hexagonal aperture
03-30-2010, 06:26 PM   #6
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QuoteOriginally posted by wlachan Quote
The # of blades determines how the shape of bokeh looks like when stopped down, but whether the bokeh would be smooth or donut like is determined by the actual optics.
QuoteOriginally posted by Lowell Goudge Quote
There was An intresting thread .. showed the difference between mAny lenses in the harshness of bokeh
it did not address the impact of round vs octagonal or hexagonal aperture
AFAIK it's a combination of blades, optics, and distance. I recently shot my ancient T2 Vivitar 200/3.5 with 18(!) blades, forming a perfect circle - and when focused on a close subject, the glittery backdrop was all big perfect circles. Bokeh balls, I call them. Shooting from a greater distance reduced their size, but they're still balls.

And a couple weeks ago I shot my Schneider Betavaron 50-125 enlarger zoom. Very strange lens, fixed-focus - you adjust for distance by zooming, so framing a shot involves dancing around. It has just 5 blades and they form a star-shaped aperture, but the bokeh is always smooth and formless.
03-31-2010, 04:34 AM   #7
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I found something weird in my shooting, i dont know if its just the optics or the blades but i compared the sharpness of a few of my lenses and found my A 50mm 1:1.4 was much sharper (8 blades) than both my DAL 18-55 (kit lens) and a M 50mm 1:2 (both with 6 blades)

I did shots at all kinds of apertures and found the images to look better with the 8 blade lens.
03-31-2010, 04:51 AM   #8
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QuoteOriginally posted by mrbob1000 Quote
I found something weird in my shooting, i dont know if its just the optics or the blades but i compared the sharpness of a few of my lenses and found my A 50mm 1:1.4 was much sharper (8 blades) than both my DAL 18-55 (kit lens) and a M 50mm 1:2 (both with 6 blades)

I did shots at all kinds of apertures and found the images to look better with the 8 blade lens.
the 50mm F1.4 lens is a very good lens, and is going to be much better than any kit lens zoom on the market. There are far fewer compromises to be made on a fixed focal length over a low cost zoom.

the M50 F2 is a bit of a surprise, it shoud be pretty good stopped down in the F8 range.

03-31-2010, 04:58 AM   #9
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QuoteOriginally posted by Lowell Goudge Quote
the 50mm F1.4 lens is a very good lens, and is going to be much better than any kit lens zoom on the market. There are far fewer compromises to be made on a fixed focal length over a low cost zoom.

the M50 F2 is a bit of a surprise, it shoud be pretty good stopped down in the F8 range.
The M50 does have a few bits of dust under the elements, but other than that its in good shape, the A50 is in perfect condition, not one piece of dust under an element, not a scratch, so i can see how it might preform better.
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