Inside Straight: It's Elemental

When I was about 13, having exhausted the limits of my Kodak Pocket Junior camera (a 120 roll-film, fixed-focus folder with a single-element lens and two shutter speeds), I pestered my father for a "real" camera until he gave in. I left the camera store the proud owner of a 2 1/4 x 2 1/4 Korelle Reflex I SLR with speeds from 1/25 to 1/500 sec, an interchangeable 75mm f/3.5 Ludwig-Dresden Victar lens, and a Weston 650 lightmeter.

My father explained that the further I closed down the aperture, the sharper the picture would be. At f/3.5, the lens was barely sharp enough at the image center; edges and corners were less so. Stopping the lens down to about f/11 provided adequate central sharpness, and it improved the corners somewhat.

Oh, to own the fabled 80mm f/2.8 Zeiss Tessar! Two magic names together promised speed plus sharpness, but, alas, the cost was more than I could afford. Within my budget, however, was a 75mm Schneider Radionar f/2.9 that was faster but slightly sharper than my woeful Victar.

To learn exactly why some lenses outperformed others, I had to wait until I became an editor at Modern Photography, whose technical editor opened my eyes to lens designs. The Victar and Radiomar were three-element, air-spaced triplets -- a design that could produce good images at apertures of f/5.6 or smaller, but was woefully inadequate at wider apertures. (This explained why we Victar owners branded them poorly made optical dogs!)

What else did I learn from him? To answer that, let's go all the way back to simple, single-element lenses and work our way up to complex zooms.

Are single-element optics still made today? Yes, indeed. The Diana, Holga, and Woca cameras have single-element 60mm (about) f/13 lenses, with one shutter speed of around 1/100 sec. They produce soft-focus, aberration-filled pictures that some find creative, others simply bizarre. (An aberration is a lens fault affecting sharpness, contrast, and clarity; there are many types.) Could optical designers produce better single-element lenses for these cult cameras? Probably, but conventional image quality isn't their purpose.

Single-element lenses with apertures between f/11 and f/18 were used in the cheapest of nonfocusing, box-type, and folding cameras (like my old Kodak Pocket Junior). Aberrations were plentiful, but engineers were eventually able to reduce them by forming the lens from two cemented glasses with complementary optical properties. Such hybrids were called doublets, and, like the triplets that followed them, at larger apertures they were still plagued by flaws.

Lens designers took a giant step in correcting triplets by replacing the single rear converging element with a cemented component consisting of a converging lens and a diverging lens of lower power. Presto: the famous four-element Tessar. Lenses of this design, notably 75mm f/3.5 Tessars, were (and are) usually very good. Of course, photographers were not happy for very long. They wanted more speed.

Engineers overcame the f/3.5 impasse by designing -- you guessed it -- a five-element lens, replacing the Tessar's single front element with another cemented component. It resulted in a series of virtually flawless, five-element, f/2.8 lenses such as the renowned Biotessar, Heliar, and Planar.

Let's turn now to "normal" lenses for 35mm SLR and DSLRs (i.e., focal lengths between 49mm and 58mm). They generally require seven elements if speedy (f/1.4 or f/1.5), and six elements if they're between f/1.7 and f/2.

There are two notable exceptions. The long-discontinued, five-element 58mm f/1.9 Meyer Primoplan, for one, sold in large numbers to bargain-hunting SLR owners, as it was much more affordable than the comparable 58mm f/2 Biotars of the day. (The Primoplan, optically, I'd class as first cousin of the dreadful Ludwig-Dresden Victar.)

The second exception appeared about six months ago when Voigtländer, founded in 1756, introduced a 250-year anniversary version of its Bessa R2M and R3M, all-mechanical 35mm rangefinder cameras, along with a 50mm f/2 Heliar lens in a collapsible M mount.

A Heliar? Was Voigtländer just picking a name from the past or did the lens really have only five elements? Expecting the worst, we subjected the 50mm to SQF tests on Pop Photo's optical bench. The Heliar turned out to be incredibly good, comparable at all apertures to the 50mm f/2 Leica Summicron-M we'd tested in 1996. Wondering how Cosina achieved this, we pressed for the details.

Cosina, which produces all or most Voigtländer glass, replied: "Newly developed, super high-index glass reduces all aberrations and allows us to realize a fast (f/2) lens with five elements." The beautifully constructed Heliar costs but a fraction of the Summicron.

What about larger-aperture teles and zooms? They might contain a dozen or more lens elements, but knowing their number and/or position will generally avail you nothing. (Yet readers don't like us to omit this from lens tests.)

The key to making some sense of optical diagrams of zoom lenses requires the lens manufacturer to explain what the devil is going on. Few do.

Canon, however, does in its informative EF Lens Work III, available from photo retailers Adorama and B&H. I've included two diagrams from the book that clearly illustrate how Canon was able to reduce the size and weight of its 400mm f/4 EF lens.

Masterpiece: These two diagrams show how Canon dramatically slimmed down the length and weight of its 400mm tele lens by altering the position, size, and type of lens elements.

A) Single-element lens: They make very fuzzy photos (ever shot a Holga?), and might make a fitting gift -- for someone you don't like.
B) Two-element lens: Camera makers cement two different (and complementary) glasses together to better control aberrations in snapshot cameras.
C) Three-element lens (A.K.A. triplet): Better than a doublet -- but only if you stop down to f/5.6 or slower.
D) Four-element lens: The internationally known Tessar, but watch out: You can't go faster than f/3.5!
E) Five-element lens: Now you're talking. Heliars, Xenotars, Planars, and Biotessars operate beautifully at f/2.8.
F) Speed takes six elements: Practically all f/1.7–f/2 lenses get by with six, but f/1.4-f/1.5 need seven.

Comments

[Michael Alderman]

I have the dreadful Ludwig-Dresden lens mentioned by Mr. Keppler. This lens fell into my hands when I inherited a Leica IIc from an uncle. However, I havent figured out how to attach the lens to the camera. They are different in size an have different threads. Is it posible that an adaptor of some type is needed? I'm a lost and would appreciate any help....Or should I just chuck the lens?