The Magical No. 9:
9 Lens Elements & 9 Aperture Blades
Let me start with an analogy: I remember when software programs were small, like 3 or 30MB, and worked fine. Through the years, more and more versions came out with more and more bugs, so patches were added to the software code. Instead of fixing root problems, more code was piled on. And so software programs mushroomed to huge resource hogging monsters taking up 300, 600, 800 MB in size.
This is somewhat similar to lens manufacturers who have convinced the buying public that more is better: more lens elements, more bulk, more weight, more plastic, and yes, more money.
What is not so openly disclosed is the fact that many of these lens elements are there to correct optical problems caused by other elements. Many because they are no longer made of glass but injected molded plastic, so we end up with an absurd 13 element, 2.5 pound, 5” long, basic 50mm plastic lens, that retails for $1000.
Manufacturers have convinced the public that older film lenses are inferior because they were not made for digital bodies. But the reality is that it is all propelled by economics. For manufacturers, there is no money to be made from vintage/used products. It is also considerably less expensive and less time consuming to do injection molding than successfully grinding and polishing a premium piece of glass . These modern lenses are made at significant profit margins and are built with an integrated life-span. This is nothing more than a nice way of saying that they are disposable, so within a decade or less you will be spending another $1000 or more.
I am not an engineer or manufacturer and can only rely on my experiences. The old formulas of quality over quantity in element count were true decades ago as they are true today. In broad terms, prime lenses with 9 quality glass elements, or less, do perform. It does not matter if it is a wide angle or telephoto. It used to be rare to see a prime lens with more than 9 elements, designers stayed away from it due to the inevitable Pandora’s box it created.
So when looking at buying a prime lens, take a look at the element count as well as the iris / aperture blade count. It is no secret that a higher aperture blade count provides a smoother and more pleasant detail in the out-of-focus areas and highlights. All together higher aperture blade counts do enhance the quality of images.
To summarize for prime lenses:
Look for 9 elements or less (less is better)
Look for 9 iris / aperture blades or as high as possible (more is better).
These are, of course, general statements, and there are exceptions like modern Zeiss lenses who perform exceptionally well with slightly higher than 9 element counts.