In this area, I am quite naive.
Lens names. Are they brand names, or category names? On another thread someone mentioned that as a Heliar a lens would be a different speed. Is that because a different company makes the lens faster or slower, or because grouping the elements differently causes it to be faster or slower?
Funny how it took years of experience to be comfortable enough to ask the simplest of questions...
David, From my limited understanding, the speed of a lens is the function of the maximum aperature diameter measurement as a comparative value of the focal length measurement. That is why fast lenses have large diameter elements and large diameter maximum iris openings. I am sure that there are other more definitive and technical explanations. But that is the way that I think of it. Hope that this helps.
They start out as brand names, but the classics, which are copied by other makers, become design names. The "Tessar" is a Zeiss brand name, for instance, for a particular 4-element/3-group design from 1902, but many Optars, Ektars, Skopars, and even some enlarging lenses are tessar designs. Ektar, however, was a name for the top quality Kodak products, and some Ektars may be tessars, but a few are heliar designs (5-element/3-groups).
This site gives some history on many of the basics:
It's kind of annoying to see Cosina using some of these classic names like "Color-Skopar" and "Heliar" on their new Voigtlander-branded lenses, because they are modern designs, largely unrelated to the classic designs. They may be good lenses, but they should get new names.
Oh, and why are Heliars a certain speed? Well, that probably has to do with the maximum aperture at which reasonable quality could be obtained and the practicality of building a lens of a certain size at the time it was produced. My 360/4.5 Heliar is huge and weighs several pounds without a shutter! Some shorter Heliars and heliar copies like the Kodak Medalist Ektar 100/3.5 lens are f:3.5 lenses. There is also an Ektar 105/3.7, which is a heliar type.
David, I forgot to address your question on lens names. The lens names (Dagor, Nikor, Ronar, Sironar, Artar etc) are assigned by the manufacturer. There are general classes of lens designs which differing manufacturers may all offer under their respective "trade" names. Each of the designs have strengths and weaknesses.
For instance, of the four lenses Donald named, the Dagor is a Goerz lens with six elements in two groups on which the Schneider Angulon is based (not the Super-Angulon or any of the later ones, though). The Goerz Apo-Artar is the model for the Rodenstock Apo-Ronar. Sironar originally referred to Rodenstock lenses that were very similar to the Schneider Symmar. Any lens made by Nippon Kogaku is a Nikkor of some sort or another, regardless of design. The earlier Nikkors had a letter indicating the number of elements, so a Nikkor-Q (quarto) was a 4-element lens, probably a tessar, and a Nikkor-O (octo) was probably a complex 8-element retrofocus wideangle lens.
If you're asking about the names then it's really marketing/branding. A tessar is both a design and a Zeiss lens. You might have gotten away with copying the design [The Xenar I think is a tessar] but you couldn't use the name. That's the reason some companies continue to use older names. If they use the name they retain the rights to the name. Somebody mentioned Kodak was calling the lens on a disposalbe camera the Ektar.
Drilling even deeper into my naivete...
Some of you rattle off groups of elements like I can rattle off films and papers. Howcome? If we're standing together at the Yosemite Tunnel View with half a dozen other Ansel Alikes, and you know how many elements and in what groups my lenses are made up of, what is it that you can tell me about my lenses or how they will see?
The question sounds a little sarcastic...I don't mean it to. I am eager to understand, and am trying to be entertaining in my approach.
The simplest lens is a single lens - like a magnifying glass. This would give a lot of aberrations, and quickly became unpopular among photographers.
The next step was to make the lens curved, with the concave side facing the subject. This got rid of a lot of the worst aberrations, but still not good enough.
Then came the "anastigmat": Two lens elements, one positive, one negative, cemented (usually) together. This was a lot better, and actually usable for photography. There was still a bit of chromatic aberration, though... Removing the front group of a Symmar or similar will show you what these are like: Not at all bad, but far from perfect...
The "double anastigmat" is, with a few variations, the basis for all modern lenses. This consists of two anastigmats with a bit of space (and an aperture) between. The convex sides of both groups face out (from the aperture).
The Tessar is a double anastigmat with the rear anastigmat uncemented - 4 elements in 3 groups.
The Heliar (original) is a double anastigmat with an added negative element midway between the main groups.
A variant of the double anastigmat is the "doppelte Gauss", or double Gauss lens. This uses a more extreme curvature to the elements, as well as slightly different glasses, to give wide field coverage. Angulos, Super Angulon, Wide field Ektar, etc. are all variants of this.
Adding even more elements can refine the properties of the lens, or change them altogether. Very few LF lenses have more than 6 elements, or more than 4 groups. Very few lenses for 35mm have fewer than 6 elements or 4 groups...