Do Aperture need to be near perfect circle?

[cthep2]

Hi Seniors,
Newbie here and would like to check regarding the Aperture opening.
Aperature stops are formed by the Aperture Blades, must the lens produced a uniform aperture blade distribution to have near perfect circle? Or simply do aperture need to be
near perfect circle?

[di0nysus]

the more circle it is...the nice the 'bokeh' will be.

lenses of higher end will tend to be more circular as they have more blades etc

[2.8photography]

nope. not all apertures are perfectly circular
open both caps on a 'D' lens and stop down - u can prob see that it isnt
this mainly affects, as mentioned the bokeh; but not significantly enough, the picture quality etc
however having a 'non-circular' aperture does give 1 benefit'

when stopping down to f/16 and smaller, u get a nice starburst effect

[cthep2]

Originally Posted by di0nysus the more circle it is...the nice the 'bokeh' will be. lenses of higher end will tend to be more circular as they have more blades etc

Hi di0nysus, many thanks for your prompt response.

So can we say that those normal kit lens doesn't really produced a better circular aperture?
Can we also say that at least the blades formed uniformly to have a respectable aperture opening? If not, would it be a quality problem?

[cthep2]

Originally Posted by 2.8photography nope. not all apertures are perfectly circular open both caps on a 'D' lens and stop down - u can prob see that it isnt this mainly affects, as mentioned the bokeh; but not significantly enough, the picture quality etc however having a 'non-circular' aperture does give 1 benefit' when stopping down to f/16 and smaller, u get a nice starburst effect

Yes, I've noticed that, however, some stops you can see that the apertures blades formed a much better circles (say f3.5,f5.6>higher) while at some are unbalanced(f4,f4.5,f5). Isn't the unbalance will affect an unbalance focus on the subject(or DOF)? (sorry really newbie here).

[2.8photography]

Originally Posted by cthep2 Yes, I've noticed that, however, some stops you can see that the apertures blades formed a much better circles (say f3.5,f5.6>higher) while at some are unbalanced(f4,f4.5,f5). Isn't the unbalance will affect an unbalance focus on the subject(or DOF)? (sorry really newbie here).

well i dont really think so
ive never had any problems with the focus
well yes, at larger apertures where the blades are in or close to their original position, it is hard to notice if it isnt circular
as u stop down a little, the un-circular shape becomes eminent, but as u stop down some more it becomes unnoticable cos the aperture is too small to notice

[Del_CtrlnoAlt]

iirc, lenses in the past are not circular, instead, they are like polygon type of shapes it takes on depending how many sides they have.

newer lenses comes with circular apertures, which is often indicated to show that the apertures are 'rounder' not perfect circle, but better roundness.

as some have said, the bokeh will show, circular aperture blades will produce a rounder shapes of flare, older type of aperture blades will produce polygons of flare.

[Dream Merchant]

Generally, yes, unless you take into consideration the 6-sided apeture of OM lenses ... which generally produce round or slightly elliptical high-lights which is Zuiko OM lenses' signature:

OM 50mm f/1.8 at f1.8



The bokeh of these cheap 6-bladed f/1.8 lenses, when handled correctly, is silky smooth:

CHEERS!

[cthep2]

So that means, it doesn't matter whether the blades doesn't produce a uniform rounded figure and it will just create different effects on the photos.

[Dream Merchant]

No, not always the case.

In many lenses, the number of apeture blades has a direct and proportionate relation to the results you get - aka, shape of high-lights, flare characteristics etc, but in some cases, like the above examples, shows that even a 6-bladed apeture lens can produce rounded OOF high-lights and silky smooth bokeh. However, don't look for that characteristic in most lenses - the roundish or elliptical high-lights seem to be something unique to OM lenses.

[grantyale]

I've seen a 18-70 that isn't equilateral when closed down...

[grantyale]

I've seen a 18-70 that isn't equilateral when closed down...

[cthep2]

Originally Posted by grantyale I've seen a 18-70 that isn't equilateral when closed down...

So what did you do...return it??

[grantyale]

It wasn't mine...
How come I double posted?

[cthep2]

Originally Posted by grantyale It wasn't mine... How come I double posted?

Oh it's not yours, have you seen a photo taken by that lens?

[grantyale]

Not too bad other than the bokeh becomes a bit elliptic.

[Dream Merchant]

Hey, check out this super circular 18-blade apeture:



KEWL huh?

[cthep2]

Originally Posted by Dream Merchant Hey, check out this super circular 18-blade apeture: KEWL huh?

cool man...18 blades..mine is just 7 blades..(Of course kit mah...)
I should have take picture and post here for you to see.

[cthep2]

See my lens (Sorry picture not that clear..)



The apertures is not smooth because the distribution of blades to form the circle is not balanced. You think this is normal?

[voldisinarta]

I am not an expert, based on my experience a near perfect circle aperture is needed in a fast lens, say f/2.8 and below. For those slower lens, it does not give much difference.

Please correct me if I'm wrong...