What information can be ascertained from "x elements in y groups"?

[SeanEsopenko]

When looking at lens specifications the number of elements and groups are often listed. What kind of information can be gleaned from this spec? Any examples?

[rdenney]

When looking at lens specifications the number of elements and groups are often listed. What kind of information can be gleaned from this spec? Any examples?

Not much that is useful. In a couple of cases, it can identify the lens design. For example, the f/8 Super Angulon design had six elements in four groups, and the f/5.6 design had 8 elements in four groups. And it can be used to identify a tessar (four elements) versus a plasmat (five or six elements), which is sometimes not obvious for some older lenses.

For lens design geeks, there is some interest and it can be used to trace the design roots or even identify a mystery lens. But for users, many other things are more important, including coverage, contrast, resolution, size and weight, rendering, maximum aperture, condition, shutter, are all direct measures of performance in any given situation.

Generally, more elements makes increases the degrees of freedom in the design, and that's probably why lens makers brag about it. But even that is probably an overstatement.

Rick "whose interest is only academic" Denney

[E. von Hoegh]

To simplify, it tells you how many pieces of glass there are, and how many are glued together. No more.
The f8 SA has 6 elements in four groups. So does a Plasmat. So do a few other designs. The f5.6 SA has 8 elements in four groups. So do some process lenses.
Without a diagram of the lens elements, it really doesn't tell you much about the design (except for a very few instances).

[Len Middleton]

Generally, more elements makes increases the degrees of freedom in the design, and that's probably why lens makers brag about it. But even that is probably an overstatement.

And of course all else being equal, adds to the cost of the lens. One would expect that there is a real or percieved problem or benefit that the additional cost is intending to address.

However with some of the older lenses, the problem may have been patent infringement, so some designs may have additional element(s) or different construction to address that issue.

The advent of lens coatings made the large number of glass surfaces viable. Older lenses typically had much fewer elements due to light loss and the resulting reduction in contrast.

[Ole Tjugen]

4 elements in 4 groups generally means a dialyte or a double Gauss - very very different lenses.

6 elements in 2 groups means the lens was designed before the advent of coatings, but it could still be 3+3 or 4+2. And there are a LOT of different 3+3 lenses, like the Dagor, the Collinear, the Hexanar, the Angulon, the Amatar - and they're all different.

24 elements in 21 groups means a big expensive zoom lens for 35mm SLR, that's about the only useful information. Oh - and it has to have very good coating. :)

[cdholden]

Adding to what Ole said, knowing how many air surfaces, along with knowledge of coating or lack of, one can take a guess as to how prone to flare a lens is or is not.

[GPS]

It can have a certain meaning when comparing lenses of the same focal length, type etc. Historically it developed as a boasting sign of more modern, complex designs, I guess, as more modern lens designs had usually more elements. I still remember boasting articles in Shutterbug about new SLR zoom lenses written in this spirit...:)

[GPS]

Adding to what Ole said, knowing how many air surfaces, along with knowledge of coating or lack of, one can take a guess as to how prone to flare a lens is or is not.

Not so. You mistake contrast for flare. Flare is much more depending on lens view angle and the size of its front element than a number of its elements and their groups.

[genotypewriter]

Not so. You mistake contrast for flare. Flare is much more depending on lens view angle and the size of its front element than a number of its elements and their groups.Flares can also be internal with complex lenses. Some call them internal reflections. Either way, we all know what we're talking about... which is what's more important... not just the words :)

[SeanEsopenko]

I had suspected it's tough to discern a lot from the number of elements & groups and that actual diagrams of lens arrangements and descriptions of the types of glass used is much more helpful. Seems that's the case from the consensus.

This question came about due to Ken Rockwell stating the lens element/grouping counts on every single one of his reviews yet he only used this statistic once in a useful way and it was more an allusion to the counts than an explicit reference. After doing some research I found he was probably correct in stating that the Mamiya 43mm lens for the 7/7II is the "original" biogon, or at least the most similar to the 75mm meant for view cameras due to the element & grouping count.

Are there any good internet articles out there on the basics of lens designs? Stuff like what convex lenses do, what happens when you group lenses together, how astigmatism is frequently corrected. Stuff like that?

[E. von Hoegh]

Any good book on optics will help you out.

I don't know about the internet, I have access to a good library.

Again, you need a diagram of the lens. Just because it has the same element/group count really means nothing.

[rdenney]

Rudolf Kingslake's A History of the Photographic Lens is a good read for non-scientists, and it will provide a good general understanding.

People like Ken Rockwell (and most of us) read books about it and recount what we read. Kingslake led the lens design group at Kodak during their heyday, when they were making the best lenses in the world. He writes from practice as much as theory. This is a required book for people interested in the topic.

Rick "preferring primary sources" Denney

[Dan Fromm]

This question came about due to Ken Rockwell stating the lens element/grouping counts on every single one of his reviews yet he only used this statistic once in a useful way and it was more an allusion to the counts than an explicit reference. After doing some research I found he was probably correct in stating that the Mamiya 43mm lens for the 7/7II is the "original" biogon, or at least the most similar to the 75mm meant for view cameras due to the element & grouping count.

Sean, the "original" Biogon was designed in 1930s and is an f/2.8 Sonnar derivative. It has 7 elements in 4 groups. The Biogon you're thinking of is an f/4.5 post-WW-II design and has 8 elements in 5 groups. It was offered as a 38 mm lens for 6x6, 45 mm for 6x7, 53 mm for 6x9, 60 mm (special for NASA) for I'm not sure which format, and 75 mm for 4x5.

According to Mamiya, their 43/4.5 for the Mamiya 7 has 10 elements in 6 groups. Not at all a Biogon, Biogon-like only by courtesy.

Ken Rockwell is not to be trusted on matters of fact.

[SeanEsopenko]

Ken Rockwell is not to be trusted on matters of fact.

Yeah I generally distrust his writings, hence why I started up the thread. I don't like openly attacking a person's opinions but I was questioning to myself why he quotes the lens elements and groupings counts in every single one of his lens reviews. I didn't see a whole lot of use in the statistic.

I have put a reserve at the public library on the Kingslake book recommended above. It seems like a good "primary source" for lens design information. I had Alan Greene's Primitive Photography back in college which was a fairly good intro to classic lens designs but I lent it to a friend who's studio/home was burnt down and haven't gotten around to reacquiring it.

Back in college I had made a simple box camera out of plywood based on info from Greene's book but time was short so I made the lens from a simple magnifying glass and just exposed on photo paper. I made dark slides for the paper, though, which seemed to impress the instructors :).

[E. von Hoegh]

Yeah I generally distrust his writings, hence why I started up the thread. I don't like openly attacking a person's opinions but I was questioning to myself why he quotes the lens elements and groupings counts in every single one of his lens reviews. I didn't see a whole lot of use in the statistic.
.

You're not attacking his opinions. You're questioning what KR states as fact, which is in fact erroneous.

Element/ group count is one of those meaningless factoids that impresses the un- or partly-informed.:)

[Dan Fromm]

Element/ group count is one of those meaningless factoids that impresses the un- or partly-informed.:)

E., I pretty much agree with you but as we've just shown the count does help separate sheep from goats.

[Leigh]

... I was questioning to myself why he quotes the lens elements and groupings counts in every single one of his lens reviews.
It's probably to distinguish different generations or versions of a lens which otherwise have the same specs.

It's also for identification since lens manufacturers include that information in their spec sheets.

- Leigh

[ic-racer]

There actually ARE some cases where industry marketing as resulted in a class of products where "more elements are better." Here are a few:

A) Some enlarging lenses by Nikon, Schneider, Rodenstock, Fuji, Komura and others. (eg. MakroSymmar HM (8) >Componon-S (6) > Componar (5) > Comparon (4))
B) Rollei 35mm cameras (the compact viewfinder camera) (Sonar (7) > Tessar (4) > Triotar (3))

However, in most cases you cannot make any good judgement. For example comparing the Zeiss to the Yashica lenses in the Yashica/Contax mount. In almost every case the Yashica lenses have one or 2 more elements.

[paulMD]

Generally speaking I would say that for a given "style" (focal length and coverage) of lens more elements means better (particularly wide-open) correction and performance. A 3-element triplet will be soft wide open, a 4-element Tessar will be sharp in the center, a 5- or 6-element Planar type will be pretty sharp across most of the field. All will be sharp at f/16. That said, you need coatings to go much beyond 4 elements, as you start to lose contrast. The more elements (technically, air-glass interfaces) the more contrast you lose.

You can't predict other characteristics, coverage in particular varies mostly based on the design. A 6-element double gauss will hardly cover anything, a 6-element Nikkor-W will have quite a lot more. A 6-element Nikkor-SW would handily beat both.