number of aperture blades a lens has and its effect

[Ron Scubadiver]

One would think as close to round would be the best, but I don't think about stuff like this much.

[Bjørn Rørslett]

My Type K version appears to have 7.

So does my K and AI of the 28/3.5. There is an H earlier model somewhere but cannot find it at present. Might even be in another lens house.

[Bjørn Rørslett]

One would think as close to round would be the best, but I don't think about stuff like this much.

The basic requirement is about the area of the opening, not abound its circularity. Fewer blades make for a snappier operation.

[Tristin]

One would think as close to round would be the best, but I don't think about stuff like this much.

For oof rendition the vast majority would agree, as do I.  For rays, I strongly prefer straight blades.  It is an issue of compromise, though it is a very easy one for most.  I don't see straight blades making a return unless someone decides to stand out by making something with 13+ straight blades. 

The Jupiter 3+ 50mm f/1.5 has 13 curved blades, so there are aome niche products out there with high blade count.  The Song G series have 11 curved blades.  Perhals when the sharpness trend has faded, we will see fompanies trying to stand out with different blade setups.

[charlie]

So does my K and AI of the 28/3.5. There is an H earlier model somewhere but cannot find it at present. Might even be in another lens house.

I've got an early version Nikkor-H with the small rear element, it does in fact only have 5 blades.

[Roland Vink]

The basic requirement is about the area of the opening, not abound its circularity. Fewer blades make for a snappier operation.

Circularity ensures the minimum edge length for a given area (f/stop), so diffraction is also minimized.

I've got an early version Nikkor-H with the small rear element, it does in fact only have 5 blades.

This is the only F-mount SLR lens with 5 aperture blades. I guess due to the wide angle of view and large DOF, Nikon decided they could get away with fewer blades since bokeh is not much of a concern with this lens. Most other Nikkors from the same period had 6 or 7 aperture blades.

[Roland Vink]

number and shape

My Nikkor-T 10.5cm 1:4 lens has an opening like that around f/5.6-8, but only 9 aperture blades. If there are specular highlights in the background (or foreground), such as light reflecting off foliage, it can produce interesting star shape blurs!

[null]

A circular aperture will produce the biggest shift in focus due to spherical aberration. Lenses with shaped apertures offset the shift. Spherical aberration basically means the focal length of the lens is not constant as you go from the center of the lens to the edge of the lens. The West-German 50/1.5 Sonnar and the current C-Sonnar both have shaped apertures, most other Sonnars have circular apertures.

[Erik Lund]

leica 21mm f4 super angulon has 4 aperture blades,,, 

[Erik Lund]

A circular aperture will produce the biggest shift in focus due to spherical aberration. Lenses with shaped apertures offset the shift. Spherical aberration basically means the focal length of the lens is not constant as you go from the center of the lens to the edge of the lens. The West-German 50/1.5 Sonnar and the current C-Sonnar both have shaped apertures, most other Sonnars have circular apertures.

So that is why so many of the Leica M lenses has these strangely shaped blades I presume,,, since focus shift is a killer for Leica M mechanical rangefinders.

[pluton]

The first generation Zeiss high speed primes for cinematography had three-sided irises, achieved using nine blades(!)...maybe they were concerned with focus shift?
To see the 3 bladed irises, scroll down at the linked site:
http://cinematechnic.com/resources/zeiss_super_speed_f12_lenses
Many Super-8 film cameras in the 1970's featuring auto exposure had two-bladed irises, yeilding a diamond shaped OOF highlight. 

[Harald]

Six Blades. I think i like the Micro Nikkor 55mm 3.5....

[John Geerts]

Great shot Harald.

Six Blades also with the Nikkor K 85/1.8  Must be the reason I adore this lens 

[Harald]

Do not show this photos in any other forum! 

[null]

I'm not sure if it is considered "First Generation"- but this 1927 Carl Zeiss Jena 4cm F1.4 uses lots of blades for a circular aperture. I think it is "Debrie" mount, under 300 made. I found of described in a Zeiss catalog of the era as "Objective of Extreme Rapidity", meaning "fast". Marketing from 90 years ago.