What happened to the old style aperture blades?

[Arcturus]

I like using vintage medium format folders (1930's-40's), and I notice that they use many more aperture blades than cameras that came after it. There are so many that the opening always stays round, or very close to round at all stops. Average modern lenses usually have the standard 5 straight blades, and premium lenses can have 6 or so. I see the same 5 blades in my 1970's TLR's and rangefinders. So why did lens makers stop using the old style aperture blades in favor of simpler ones if they make those out of focus pentagons that many people find objectionable?

I found a picture on Flickr that shows the type of aaperture blades I'm talking about.
http://www.flickr.com/photos/nesster...ol-camerapedia

[Jeff L]

Best guess would be $$$
...and maybe speed requirements of auto apertures.

[artobest]

Interesting subject. Yet, in my opinion, bokeh, being an unquantifiable characteristic, is very fashion-led. My Zeiss/Rollei lenses have five blades and produce noticeable pentagon-shaped specular highlights, miles from the 'creamy' softness we are all supposed to aspire to, but to me, this out-of-focus rendering is highly picturesque and often rather beautiful.

[thegman]

Interesting subject. Yet, in my opinion, bokeh, being an unquantifiable characteristic, is very fashion-led. My Zeiss/Rollei lenses have five blades and produce noticeable pentagon-shaped specular highlights, miles from the 'creamy' softness we are all supposed to aspire to, but to me, this out-of-focus rendering is highly picturesque and often rather beautiful.

Indeed, I'm not into shallow-DOF at all, I'd rather most of my photos had front to back sharpness. But all things considered, I'd rather a more natural rendition of OOF areas. It is of course a fashion thing though, and the current craze for Noctilux-style, shoot everything at f/0.95 will likely go away soon enough.

[jp498]

I'd have to guess the smooth/creamy aesthetic must have went out of style for a while in post modern photography. If you were 100% in focus groupf64 style shooting, it doesn't matter, just like iris shape isn't important in the enlarger because ever piece of silver is in focus. Shutter choices are a big part of this. Old pre-war compound shutter have more blades than copal for example. Copal 3's have more blades than copal-1's but I'd guess that's a because it's a bigger opening, not just because they can.

In LF many of the barrel lenses (no shutter) have lots of nice curved blades. I like these and use them with the focal plane shutter of the speed graphic. Quite a few options for old lenses and aperture styles in LF.

[Matthew Wagg]

The only lenses I have that have lots of apeture blades is my Pentacon 4/200 which has loads, its circular at all apetures, unfortunately it doesn't focus close and its focal length is of limited use to me. I'd love a 50 and 85mm with as many blades.

[BetterSense]

Quality standards.

Lens manufacturers realized that they could get away with going cheap, so they did. The least-common-denominator mechanism at work.

[tony lockerbie]

The optical design also has a lot to do with the quality of the oof areas, not just the aperture blades, although they can help a lot. I personally like using shallow dof for certain photographs, gives a more pleasing 3D effect, so the quality of the oof areas are very important (notice that I haven't used the "B" word yet)
I suspect like others have stated, that the dollars have caused the modern trend towards minimal blades, but also the auto diaphragm function must require less moving parts. It is pleasing to see that some manufacturers are coming back to designing lenses that have a more pictorial quality rather than clinical sharpness (Cosina/Voigtlander are a good example)
From an aesthetic point of view, those old multi bladed apertures are a thing of beauty.

[rawhead]

I'm with Tony; my best guess & understanding is that the 20-blade diaphragms of late would be an extreme pain in the ass, if not outright impossible to implement in modern auto-focus / auto-aperture lenses. With the advancement of technology, remember, so has increased things like FPS; when you have a camera *body* (and shutter mechanism) that touts 12 frames a second, during which the aperture blades need to open up and stop down 12 times per minute as well, there is huge demand being placed on the rigoursness of the blade.

This explains why even high-end (e.g., Canon L) lenses tend to be very limited in terms of the number of blades (e.g., 5). If cost was the number one reason, then we would expect that the high-end, premium line of lenses to have more blades.

[Arcturus]

I can see how auto exposure and rapid fps would be a problem with so many aperture blades, but even more recent manual aperture lenses have only five or six. Maybe it's both the cost and/or auto exposure, depending on the camera. The out of focus area isn't important to me since I mostly do stopped down zone focusing, but it seemed strange in this bokeh obsessed day and age.