Author Topic: number of aperture blades a lens has and its effect  (Read 17778 times)

oldfauser

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number of aperture blades a lens has and its effect
« on: March 04, 2016, 01:57:53 »
I was looking over my collection of Nikkors, and noticed that they all have 7 aperture blades - not one has 9 (or 6)!

am i missing something? Or is this something not to worry about... Should i look at getting a 9 blade lens in the future?

Thoughts?

Art

Jan Anne

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Re: number of aperture blades a lens has and its effect
« Reply #1 on: March 04, 2016, 02:08:55 »
Depends on your shooting style.

If you shoot these lenses closed down with boke balls in the background you will see less round circles, wide open it doesn't make a difference as with most lenses the inner barrel determines the wide-open aperture characteristics and not the aperture blades themselves.

Personally I use my lenses wide open most of the time so don't care about the amount of aperture blades, other character aspects are way more interesting IMHO :)
Cheers,
Jan Anne

Bjørn Rørslett

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Re: number of aperture blades a lens has and its effect
« Reply #2 on: March 04, 2016, 02:43:18 »
Early Nikkors had 7 and with time 9 became more common.

The more the number of blades, the more circular opening as the aperture closed down. In the '50s, lenses having a large number of blades were frequent. However, there are drawbacks as more blades meant a more complex mechanism. This is important as the aperture operation became linearised with the arrival of TTL metering towards the end  of the '70s and this in conjunction with motor drives and demands for faster operation spoke against the high-numbered aperture design.  Modern optical designs try to balance the shape of the aperture opening against other desirable optical qualities. Thus, more blades usually confer a smoother out-of-focus rendition.

Tristin

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Re: number of aperture blades a lens has and its effect
« Reply #3 on: March 04, 2016, 03:05:27 »
The number of blades also determines the number of rays rendered on point light sources (sun/starbursts) as well as the shape of the rays. Odd numbers double the points,so 8 blades makes 8 rays while 9 blades makes 18.  Curved blades cause the rays to fan out as the grow longer, while straight blades cause more focused rays that narrow to points. Ai-s lenses are more commonly found with 9 blades on the faster versions of a given focal length.

Roland's page is extremely handy for these details.
-Tristin

David H. Hartman

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Re: number of aperture blades a lens has and its effect
« Reply #4 on: March 04, 2016, 04:47:49 »
The [edge of each blade causes] diffraction with one spike going outwards and the other inwards. With an odd number of blades the spikes don't over lap so you get two times the number of spokes with half being slightly stronger than the other half. [With an even number of blades, opposite blades reinforce each other's spokes for fewer, stronger spokes.] I prefer a nine blade aperture that is quite round at larger apertures becoming more of a polygon at smaller apertures.

There are other image consideration than diffraction stars and point light orbs. I'll have to poke the web to refresh my memory or I'll shortly have my foot deep inside my mouth.

Dave

Edited per Roland's post below.
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Roland Vink

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Re: number of aperture blades a lens has and its effect
« Reply #5 on: March 04, 2016, 09:03:39 »
The intersection of two blades cause a diffraction spoke ...
NO, it's the edge of the aperture opening which causes diffraction. Diffraction is an edge effect - light passing near the edge bends a bit. If the edge is straight the light all bends in the same direction so you get a directional diffraction spike on your image. Lenses with rounded aperture blades cause the diffraction to spread out evenly in all directions which causes a diffuse halo around point sources of light instead of a diffraction star.

Also, because diffraction is an edge effect, it becomes greater at small apertures since the edge / area ratio increases.

To the original question, there is nothing wrong having all lenses with 7 aperture blades. I think it is a good feature. Lenses with 6 or 8 aperture blades produce less interesting defocus blurs - the shapes are too regular and "square". Having an odd number if sides looks more natural and organic to me.

The very first F-mount Nikkors had 9 aperture blades, but they soon reduced to 6. The earlier rangefinder lenses had as many as 16 aperture blades. Rangefinder lenses are always stopped down to the shooting aperture, they don't move when the picture is taken so the aperture mechanism can afford to be heavy and well-built. However SLR lenses must have an aperture which opens and closes very quickly - wide open for TTL viewing and then stopping down instantly at the moment of exposure. Therefore the aperture blades must be very lightweight so they can move quickly. Maybe the early 9-blade apertures were too heavy with too much friction to operate quickly, or they were too complex and expensive. During the 1960s and 70s the number of blades changed to 7, possibly because it is a nicer shape. Lenses with very fast aperture, and telephotos had 9 aperture blades to give the opening a rounder shape, since the shape of the aperture is more noticeable in pictures taken with these lenses.

richardHaw

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Re: number of aperture blades a lens has and its effect
« Reply #6 on: March 04, 2016, 09:15:10 »
An oddity for the f-mount  :o :o :o
Odd numbers feel more organic. i am yet to meet a person who prefers 6 bladed irises.

by the way, if i am not mistaken, the 28mm f/3.5 only has 5 aperture blades. i have cleaned 2 so far and i remember that they only had 5...i can check later

Almass

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Re: number of aperture blades a lens has and its effect
« Reply #7 on: March 04, 2016, 09:45:13 »
Ohhhhh. They sold me a rubbish lens with too many blades........









David H. Hartman

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Re: number of aperture blades a lens has and its effect
« Reply #8 on: March 04, 2016, 10:47:30 »
Roland,

Thanks for the correction. It's obvious now that I've thought it out.  :-[

Best,

Dave
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Bjørn Rørslett

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Re: number of aperture blades a lens has and its effect
« Reply #9 on: March 04, 2016, 11:08:29 »
Ohhhhh. They sold me a rubbish lens with too many blades........

I have Russian lenses from the '50s with up to 21 blades ....

By the way, the optics indeed were rubbish, but I doubt the aperture was the main reason.

Bjørn Rørslett

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Re: number of aperture blades a lens has and its effect
« Reply #10 on: March 04, 2016, 11:17:26 »
I have enlarger lenses with 3 aperture blades. A Schneider-Kreuznach cine lens (used by me for photomacrography) have 4 giving peculiar highlights ... Early Hasselblad lenses had 5, and the Nikkor-S 35 mm f/2.8 had 6.

ArendV

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Re: number of aperture blades a lens has and its effect
« Reply #11 on: March 04, 2016, 12:02:08 »
number and shape

Arend

Tristin

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Re: number of aperture blades a lens has and its effect
« Reply #12 on: March 04, 2016, 17:52:29 »
Arend, wow.  That is strange looking!  What kind of rays does that produce?  I can imagine the strange bokeh.

I hope we see a retur n in using straight blades someday.  I'd rather have a higher number of straight blades personally, though I know I am a minority
-Tristin

pluton

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Re: number of aperture blades a lens has and its effect
« Reply #13 on: March 04, 2016, 18:10:08 »
Schneider-Kreuznach made a lot of enlarging lenses in the 1970's(and maybe later) with the 'reversed curve' blades.  I cannot imagine that it helped the imaging performance of the lens, but maybe it didn't hurt?
Keith B., Santa Monica, CA, USA

Chip Chipowski

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Re: number of aperture blades a lens has and its effect
« Reply #14 on: March 04, 2016, 18:55:30 »
Quote
by the way, if i am not mistaken, the 28mm f/3.5 only has 5 aperture blades. i have cleaned 2 so far and i remember that they only had 5...i can check later

My Type K version appears to have 7.