Uneven aperture blades?


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H4lcyon

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Jul 14, 2008
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#1
Hi guys, I have a question regarding aperture blade opening of a lens. Does the blade opening have to be perfect and even on all side or can it be uneven like the pictures here?
(my 18-70 3.5-4.5)

Opening at smallest aperture. You can see the uneven sides.


Mid-sized. One side is already a circle but the other side is still angular.


Widest. It's a nice circle.


I have another lens (50mm 1.8) and it looks perfect there. I'm just wondering whether I should bring it for service or just keep it for now, there's already some dust collecting inside it anyway. I don't think I see any effect on my pictures though.
 

zac08

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Feb 21, 2005
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#2
I guess the blades might be a lil sticky there. Or that it is not able to match the others in the positions required.

You probably can inquire if someone can try to fix this for you at Nikon. Else you can check with Fatique if he can help you with this issue. ;)
 

grantyale

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Oct 4, 2004
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#4
I've seen two AFs 18-70 lenses, both have uneven aperture blades.
 

Snoweagle

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Jan 26, 2005
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#5
Aperture blades are like that. U won't get a perfect shape at smaller apertures, even for those with 'circular' blades.
 

Apr 15, 2008
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#6
:bsmilie: Thanks for clarifying. But why then do bokeh'ed regions look circular when the aperture blades form an opening that isn't circular? :dunno:
 

calebk

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Jul 25, 2006
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Clementi
#7
:bsmilie: Thanks for clarifying. But why then do bokeh'ed regions look circular when the aperture blades form an opening that isn't circular? :dunno:
Actually, they don't. You have a 50/1.8; stop it down to f/4 and shoot with highlights in the background, you will notice that they take on the shape of your aperture opening.
 

zac08

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Feb 21, 2005
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#8
:bsmilie: Thanks for clarifying. But why then do bokeh'ed regions look circular when the aperture blades form an opening that isn't circular? :dunno:
coz the Bokeh'ed regions are normally from wide open lenses.. and they are generally round at that stage. ;)
 

Rashkae

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Nov 28, 2005
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#10
Aperture blades are like that. U won't get a perfect shape at smaller apertures, even for those with 'circular' blades.
Depends on the lens too. Most of my lenses maintain a circular shape till about f/5.6, but after that the aperture blades remain in a fairly symmetrical shape
 

calebk

Senior Member
Jul 25, 2006
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Clementi
#11
Aperture blades are like that. U won't get a perfect shape at smaller apertures, even for those with 'circular' blades.
Depends on the lens too. Most of my lenses maintain a circular shape till about f/5.6, but after that the aperture blades remain in a fairly symmetrical shape
Same here too...the five-bladed aperture on my 35mm f/2 is a symmetrical pentagon when stopped down.

Snoweagle, do you have any additional info that backs up your statement?
 

Apr 15, 2008
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#13
Actually, they don't. You have a 50/1.8; stop it down to f/4 and shoot with highlights in the background, you will notice that they take on the shape of your aperture opening.
coz the Bokeh'ed regions are normally from wide open lenses.. and they are generally round at that stage. ;)

ahh, i see.Thanks a lot! :sweatsm:

didn't exactly measure the dimensions of OOF points of light in my photos :bsmilie:
 

calebk

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Jul 25, 2006
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#14
ahh, i see.Thanks a lot! :sweatsm:

didn't exactly measure the dimensions of OOF points of light in my photos :bsmilie:
Haha no its not the dimensions; it's the shape. With a five-bladed pentagonal aperture, you will get pentagonal highlights when you stop down.
 

zzyzx

New Member
Aug 25, 2007
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#15
hmm...after reading snoweagle's post i tried on my two lens and both got even aperture blades leh...

i'm also pondering.. for extreme case if one of the several blades doesn't close at all, would it affect the DOF of the image since more lights went thru and also the exposure etc?
 

zac08

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Feb 21, 2005
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#17
yea...the dimensions of the shape? :bsmilie:
The dimension do not matter as they are made from the light source. The larger the source, the larger the shape.

It's the shape of the it tat matters... the rounder, the better the aperture blades are able to make a circle. And normally you'd see it clearly when shooting wide open. This is when the blades are fully RETRACTED, you dun even see them...
 

zac08

Senior Member
Feb 21, 2005
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#19
I have seen more than 20 of this lens.
Most of them got uneven aperture blades

There's no problem with your lens
Problem with the construction? Or design issue?
 

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