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

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

    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?

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

    Quote Originally Posted by SeanEsopenko View Post
    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

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

    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).
    One man's Mede is another man's Persian.

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

    Quote Originally Posted by rdenney View Post
    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.

  5. #5
    All metric sizes to 24x30 Ole Tjugen's Avatar
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    Re: What information can be ascertained from "x elements in y groups"?

    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.

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

    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.

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

    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...

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

    Quote Originally Posted by cdholden View Post
    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.

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

    Quote Originally Posted by GPS View Post
    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

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

    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?

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