Anyone diving through the nichiest camera lenses on the market is bound to have come across the Helios 44-2 at some point. Intrigued, they might find it and buy a version of it on eBay for $30 USD and receive it in the mail a month later from the Ukraine. Any further reading will reveal its initial posturing in the 1960’s, and a host of other M42 mount lenses able to purchase from the same anonymous seller. Not a whole lot outside of those modern details are available, however.
To be perfectly honest, it appears that even less is known about the 44-2’s younger brother, the Helios 40-2, and its history. Save for the fact that, like its older brother, it is a copy of the Carl Zeiss Biotar formula, which is mostly what the 44-2 is known for. The 44-2 is nearly ubiquitous, as it’s common, it’s cheap, and there are literally millions of them out there. What’s strange is that the actual history of why these lenses matter so much is lost or hitherto untranslated.
Carl Friedrich Gauss’s telescope lens assembly was the one that really opened the doors; the granddaddy of all modern lens designs known as the Gauss lens developed in the early 1800’s. For a century Gauss’s lens design was used in telescopes the world over, being used to take some of the first astrophotography through the barrel of telescopes at observatories, and eventually was modified and improved upon for the next 200 years (1). Through the late 1800’s, the Double Gauss lens design would be perfected in a raw, workable way. It took the original Gauss lens, and effectively multiplied the number of glass elements from a base 2 (in a Gauss lens) to a 4-element group before the end of the 1880’s. This 4-element formula was created to reduce chromatic aberrations over a large focal plane.
Chromatic aberration is a term for a color impurity that a lens might produce, as a result of a lens not accepting light rays properly. Poorly-built lenses with uneven glass surfaces relative to the next can amplify these impurities, so more complex systems of multiple lenses are slightly tougher to get working in the right order. While the effect of less impurity is immense, the task of lining up separate pieces of glass elements in, say, a 200mm telephoto lens can be even more immense.
The focal plane is the distance from a lens where all the rays of light coming through the glass line up as exact as they possibly can. This is measured normally as an f-number (otherwise known as aperture), where the lower the number, the thinner the focal plane (otherwise known as focus). When an f-number is low, the lens is considered wide open to light, and therefore the rays of light coming in would have to be at a certain position in order to be seen properly in the final exposure: they would have to be in focus. Any manual lens you can find in a store these days will allow you to control exactly where that focus, that focal plane, is. The tradeoff of this, is that when you have a maximum aperture of f/1.2, you can also accept much more light and blur the background more effectively. Therefore, these sub-f/2 lenses are quite a commodity in the photography world, as they can act in extremely low light situations and operate effectively when paired with the right camera. Focus and focal plane are also commonly called depth of field, to communicate the area of sharpness in the final exposure after the photo has been taken. Focus dictates where the focal plane is, and depth of field is the final product that results from tuning your focal plane and subjects.
Bokeh is a byproduct of having foreground subjects in focus; the blurry, swirly background of things out of focus that we’ll cover a bit later on.
Simply put, a 35mm f/1.2 lens will have a much sharper, shallower focus than a 35mm f/5.6. However, at f/5.6 on the same lens, more can be in focus, but you accept less light by closing the lens slightly. This is most easily seen on a manual/variable aperture lens where you can physically rotate the aperture blades in the lens and see it working.
What part of the Double Gauss design did in the process of reducing those aforementioned aberrations was introduce more elements and achieve a lower f-number, if designed properly.
In the 1840’s a man named Carl Zeiss was creating microscopes under his namesake company in Germany. Over the years the number of employees in his shop grew until the early 1880’s when his company became the entity we know now as Zeiss. An optical and medical technology corporation known for precision and accuracy in their products, at the time, their repertoire would grow considerably.
An employee at Carl Zeiss Jena, Paul Rudolph, is credited with developing the first lens that completely corrected for chromatic aberration and astigmatisms (when rays of light have different focal planes) in 1890: the Zeiss Protar lens. Impurities at the time were mostly a product of coating technology issues as well as the use of inferior glass composition. Up until the 1880’s it wasn’t known that aperture affected depth of field. And it wasn’t until the late 1880’s that a superior chemical formula for glass composition was discovered. Before 1890, nearly all lenses were created using soda lime glass, a rather primitive production process (melting the raw materials all together) and a molecular structure that had heavy optical impurities for photographic applications. You commonly find this kind of glass used for producing bottles or window panes. The advent of borosilicate barium oxide glass in the late 1880’s allowed for Rudolph to develop the Protar lens, cutting down the competition and setting up a chemical formula basis on which all modern lenses are now built upon.
If the Double-Gauss meniscus assembly was the shape and structure of the modern lens, the Protar formula was the chemical composition that rocketed the design to new heights.
Rudolph succeeded in creating the Zeiss Planar lens formula in 1896 (2). The Planar lens added 2 more elements, remaining symmetrical and giving faster apertures. Planar being the namesake for the use of two symmetrical flat glass elements; planes. This improvement manifested in the clarity of the image, and even less issues with astigmatisms. Lower dispersion meant less scattering of photons, which in turn meant less optical impurities. Zeiss was the premiere optics manufacturer in continental Europe and remains today to be among one of the best manufacturers of glass in the world. Silent films, large bellow-focus cameras, and moreover single-lens-reflex film cameras would see the use of lenses developed with Planar formulas for well into the 60’s.
After multiple attempts by Taylor-Hobson, an English optics manufacturer, to develop their own Planar type lens, they achieved the Lee Opic, with significant improvement over the planar formula. The objective of their project was to improve Zeiss’s Planar work in 1896 to further correct for chromatic aberration. Their work was ultimately commercially unsuccessful, and they attempted twice to improve the formula again, succeeding in releasing faster lenses under the ‘Speed Panchro’ and ‘Super Speed Panchro’ designs with as fast as an f/1.4 aperture (3). Even Kodak was trying to improve upon Taylor-Hobson’s designs and up the ante in the mid-1920’s camera market while Zeiss fell back onto another of Rudolph’s designs to use while they sorted out issues with the 6-element Planar design.
While having an inferior image quality, Paul Rudolph also developed the Tessar lens formula in 1902. It was a 4-element, asymmetrical group, that at the time capable of a maximum aperture of f/4.5; still leagues away from catching up with the Super Speed Panchro and losing the title of fastest lenses out there to Taylor-Hobson.
For the moment, the Planar lenses were left in the dust as far as the still photography market was concerned, remaining popular in cinema into the 1920’s. While still a very sharp lens design, they suffered flaring issues due to the convex nature of its outer glass elements and yet-undeveloped coating technology to deal with better dispersion and help with the flaring problems. Most would prefer using the Zeiss Tessar lenses, which were a newer, if slightly inferior, formula. After all, having so many pieces of glass between a source of light and a film strip will amplify any glare a few times over, if not dealt with properly. The Planar lenses drop out of favor for the next 30 years or so, after Taylor-Hobson’s dramatic improvements over the design. They would come back when lens coating technology took hold in the 1950’s, to finally solve their flaring issue, and allowed some of the fastest lenses in the world to be produced; the mythic Carl Zeiss Planar 50mm f/0.7, and for the medium format Hasselblad 2000 and 200 series, the Planar 110mm f/2 telephoto (4).
Before we move on to the advent of the Biotar line, it’s worth discussing the pedigree of Zeiss lenses in the mid-20th Century. The Zeiss Planar 50mm f/0.7 was developed for use by NASA in 1966. For NASA so the moon could be photographed in darkness, and Stanley Kubrick used them to shoot a scene of one of his films only lit by a candle (5). Zeiss kept one, NASA got six, and Kubrick got three. In both applications, it excelled. Only ten of the lenses were made, and if someone were interested in purchasing one, they would likely offer a fair price of $25,000,000 USD to start.
The Zeiss Biotar line had its rumblings in the early 1920’s while Taylor-Hobson was hard at work on their Panchro series. It was a revisiting to the original Double Gauss design by Zeiss’s optical engineers, at nearly the same time as another German lens manufacturer, Schneider. Schneider released their version two years before Zeiss struck, with their Xenon lens formula. Biotar, however, was developed independently, and both formulas arrived at the same conclusion. Instead of using a strictly symmetrical glass design, they determined that a 6-element lens with 3 wide outer elements could possibly fix their current issues with the Planar formula. In 1927, the Zeiss Biotar 50mm f/1.4 was developed for film cameras, and for still photography the Zeiss Biotar 58mm f/2 was released in 1936. It was the first widespread lens for 35mm single reflex cameras of the day, with primary benefits of the design being its weight and dramatic improvements over the Planar designs. It also showed that a 6-element lens was incredibly viable for the day. It was standard on multiple kits issued by Kine Exakta and Ikon, two of the first 35mm platforms (6). Users quickly noted its focus throw had the uncanny bokeh that is associated with those early designs, with the backgrounds at maximum aperture adopting a swirly, dream-like bokeh with an expectedly sharp depth of field in full focus.
Zeiss finally had a breakthrough in the competition with Taylor-Hobson with the 58mm f/2, and while Schneider lenses were a bit more popular overall, Zeiss was busy at work trying to introduce the Biotar improvements to the Planar formula. Before World War II breaks out on 1939, Zeiss also comes out with the Zeiss Biotar 75mm f/1.5. One of the fastest mid-telephoto lenses of its time.
It’s also worth noting that in the modern photography industry, Japan has a massive hold on the world market. Brands such as Canon, Nikon, Pentax, and Fujifilm all base out of the Pacific island nation. Those corporations had a market during this time, and their own technology rapidly accelerated after the 1930’s, but it wouldn’t be until after World War II that they would enter the global market.
Speaking of which, now with World War II now kicking up production all over Europe, a company in Russia had the distinct responsibility for military optical engineering and manufacturing under the same roof, as its tactical position near Moscow rendered it safer than other factories could ever be. This is where Helios is from, the Krasnogorsk Mechanical Works (KMZ) in Krasnogorsk, Russia (7). It exists today as a joint stock company, as it did back during the war, and is still responsible for the manufacturing of many steel and glass works.
In one of the most interesting moves the Soviets made during the war, as East Germany was occupied, they would steal the Biotar formula from a Zeiss factory. Taking it back home with them, the KMZ optical engineers found themselves with the latest in German optical advancements. One of the many gifts from the defense of their land.
The Biotar formula was a war prize.
While the KMZ developed all manner of scopes and recon equipment during conflict, when the war settled, they focused on cameras and their lens technology. Nikita Khrushchev at this time stressed production of consumer goods, so the KMZ had freedom to go after concept cameras, new lens designs, and creating their own versions of Lecia and Zeiss technologies for Russian citizens and beyond. These projects would find themselves under different names, but their production would all take place at the KMZ.
Zorki was one of these projects, being a copy of a Lecia rangefinder camera. After more research and development, the KMZ found itself being a titan of a plant, with their newfound projects flooding European markets. Zenitar (Zenit) cameras emerged from that 50’s and 60’s eras of looking for that hook in a civilian market (8). 1953 saw the first roll out of Zenit cameras, with sometime later the Jupiter lens designs. And in 1958, another one of their other European-based projects would finally be revealed to pair with the Zenit SLRs; the original Helios 44-2. The stolen Biotar formula, modified and put to work as an M42 mount lens.
From 1958 to 1999, the KMZ turned out untold amounts of the 44-2, earning it a place among the most mass-produced lenses in the world. This allowed it to dominate the marketplace for fast, inexpensive portrait lenses. Like its much older brother, the Zeiss Biotar 58mm f/2, the Helios 44-2 has a maximum aperture of f/2 and a focal length of 58mm. It was designed with a variable number of aperture blades and minimum apertures over time, but those two aspects above stay the same. One distinct practical difference between the two lenses was the characteristic softness of the Helios compared its much sharper Zeiss counterpart.
Bokeh is what the Helios 44-2 is known for these days, with the background developing an incredible swirl pattern, just enough to be tasteful and not enough to detract from the subject in the foreground. The bokeh and softness combined make photographs taken with it stick out considerably from a crowd, as the bokeh itself is easy to recognize.
While the Zeiss version was definitively sharper, the softness of the Helios was much preferred by users, escalating the dreamlike look exponentially while retaining great image quality. This is not to say the Helios is a flawless lens. Chromatic aberration is in spades, with color fringing quite noticeable at maximum aperture, and the focus was incredibly blurry outside of center metering. These two flaws combined may not have been terribly noticeable on black and white film, but on color the advantage was on Zeiss’s older Biotar lens.
Still, Zeiss had moved on from the Biotar formula by the time the Helios 44-2 was being produced, now focusing on the undertakings related to improving their older Planar formula and bringing it back to the stills market. Zeiss was also trying new designs like convex outer elements and telephoto zoom designs. So, if you had an SLR in the 60’s and were just looking for a lens to throw on it, the advantage was in KMZ’s favor.
That is the story of how Helios came to find a place in such a competitive time for the optics industry. By copying and modifying an existing lens design, they had arguably improved the Zeiss Biotar design, but laterally and in a linear fashion. It’s the same idea, not better or worse, but a different flavor of that original design, still standing 70 years later. So common that it’s even a good manual-focus alternative to many of the fast autofocus 50mm lenses out there today.
Given all that, what about the Helios 40-2? After all, that’s how we started this journey.
When Zeiss released the 75mm f/1.5 lens in 1939, they gave KMZ another European project to emulate and put a spin on, and that’s exactly what the Russians did.
In 1969, to add to their portfolio after multiple Jupiter lenses (based on the Planar design) and the success of the Helios 44-2 just a decade earlier, the Helios 40-2 was released. It surpassed the Biotar 75mm and went directly to a longer focal length of 85mm. The 40-2 was just as fast, being a maximum aperture of f/1.5. It was similar in most ways, except for a noticeable few that, like the 44-2 compared to the Biotar 58mm, modified an original design without positive or negative effects, with perhaps the most interesting note on its design is that instead of using their stolen Biotar formula, the 40-2 resulted from reverse-engineering the modifications to the original Planar formula developed by Rudolph (8). It was a Soviet Biotar, with the optical engineers of KMZ rebuilding the Biotar formula from the ground up, starting with the Planar formula. So really, the 40-2 is a KMZ retelling of the evolution of the Planar lens formula, not a true Biotar copy like the 44-2 is.
Considered the whole time, however, was the dual use of their optical products. Having a hand in military optics before, the Helios 40-2 was also positioned for use in oscilloscopes. Some have pointed to the KMZ’s dual-use manufacturing considerations as the reason for many flaws present in their lens designs, but I digress.
With the advent of their own true design, more effects were seen: soft vignetting, an extremely sharp depth of field that could make focusing difficult at times, a heavy weight, and even more pronounced bokeh than the 44-2. Any or all of these can be taken as a flaw, depending on your stance when it comes to the Helios lenses. In practicality, the user must be a bit more creative with their compositions, as the lens itself does not fare too well being at maximum aperture.
Due to the prevalence of the 44-2 and other mid-telephoto portrait lenses (most notably in the cheaper Jupiter line), the 40-2 didn’t do as well in a saturated market. Production of these lenses continued, enjoying little commercial success, but it wasn’t the beast from the east that the 44-2 was, nor the direct Zeiss copy the Jupiter 9 lens was. The Jupiter 9 and Helios 44-2 make the pair of the 60’s for Soviet camera enthusiasts (9).
You can find the 58mm f/2 Helios 44-2 out and about in the world, with upwards of eight million in production out there and Zenitar putting them in reproduction. It is the clear winner when it comes to the mid-century lens race. As a result, the 40-2 is much rarer to come across in the wild, and although its effects are more pronounced, it is unwieldy to use outside of a controlled studio environment.
I should clarify, not much information is known about these lenses in English, as many of the sources for which I’ve gathered information about the KMZ and Helios line are from Russian articles, archives, and community blogs (10). That’s for the history, and though we’ve discussed the 44-2, what about the 40-2 in use?
Zenit launched a reproduction of the Helios 40-2 out of the KMZ in 2015, and so for an import fee and around $500 USD, you can get a modern version of the original Russo-Biotar bokeh monster.
I was able to order mine directly from Zenitar, and with it came a wonderful little box, a manual for use, and a bag with a strap that held the lens. I initially ordered an EF mount version but wanted to get an M42 version, so I could use my existing adapter that I have for my Helios 44-2 to my e-mount Sony Alpha 6300. The return was easy and processed almost immediately, and I had the M42 version in my hands less than a week later, ready to use. No qualms there. I should add that I also got a protection plan on the lens, just for safe keeping.
Much of it is the same as it was when it released, with only some aperture blade difference and updated coatings appearing on the 2015 version. The weight, the focus ring, aperture ring, and overall construction are the same as they were was 50 years ago.
I can tell the difference between the 40-2 and the 44-2 immediately because of the distinct effects of each, with the 40-2 of course making itself preset in the enhanced effects of the 44-2.
Cosmetically, the 40-2 is really strange-looking for a prime lens. To have the wider maximum aperture, the center of the barrel bulges considerably to make way for the aperture blades on the inside. It is quite long, and the front glass element is sunk into the metal to act as a small lens hood, similarly to the 44-2’s deep front element.
Since I mentioned the protection plan I purchased for it, it’s worth mentioning one moment where I almost used it in the two months I’ve owned it so far. To cut a moderately lengthy story short, it was pretty much hurled at a doorframe as hard as someone could force it with the palm of their hand. I could see exactly where it hit the doorframe: a bit of missing paint from the aperture ring. No other damage occurred. The 40-2 is a leviathan construct.
It is a heavy lens, weighing more than the body of my camera itself. Thankfully, the e-mount threads are hardy enough to handle the weight, and I often use a Peak Design camera clip to mount my camera on my belt when not in use. Even walking around all day in Seattle and Olympia with it, I didn’t fatigue from its weight in any way. I would say it’s pleasant to hold. It can take quite the hit because it’s built like a tank, and coupled with the Smallrig cage for my 6300, they make a fun pair to use.
The focus throw is the first thing I’ve seen criticized by others, as turning the focus ring from one meter to infinity takes three quarter turns of the left hand. It is not for shooting fast, it is for shooting with a very crisp depth of field with a very fast aperture. That doesn’t mean it is physically quick to set up an image to expose whatsoever. While I can easily walk on the street and take shots while moving with a Sony 18-135 OSS lens; the Helios 40-2 is much tougher to use in this application, for instance.
With this, we turn to the aperture locking ring, which is an interesting choice to keep intact on a modern version of the lens. If you wanted to shoot at, say, f/5.6, you would have an aperture ring to turn which would open and close the aperture blades mechanically. On the Helios 40-2 (like the 44-2), there also exists an aperture lock, where you have a variable ring from maximum aperture to minimum aperture that locks the aperture ring from going any further than a set minimum aperture. This exists so that if you needed to focus and shoot a photo in a lower aperture than f/1.5, you could lock the aperture ring at your desired shooting aperture, open to maximum to get focus, and then close it down to your set aperture once you’ve achieved focus. This was a quirk of manual focus SLRs, as the only way to get a good view of what you were shooting at was with a wide-open lens.
This is a very old school method of shooting, and like focusing already, means that taking shots with the 40-2 takes a considerable amount of time. Even on my A6300, with focus peaking, I notice the 40-2 being very temperamental with its depth of field. As with other fast lenses the extremely shallow depth of field, this thing can be tough to get focus. Because of this, I tend to shoot with my aperture lock at f/2.8.
Speaking of focus, the Helios 40-2 has an insanely center-weighted focus. Outside of a circular zone in center frame, everything else drops out of focus drops off quickly when you’re shooting close to maximum aperture. I find aperture does best for overall focus above f/4.
Color is fantastic, with some very vivid color and juxtaposed muted contrast. This lens is more niche than anything else I’ve ever had my hands on. You can understand how this is made for portrait photography when you get it in your hands. The best photos I’ve gotten using the lens have been when I frame the subject like I’m taking a human portrait, so street photography with this lens devolves into architectural/environmental portraiture. Landscapes are bleak without a subject to center, but people are intensely easy to photograph with this lens.
This was the point that I stopped using the 40-2 on a crop sensor camera body.
I’ve had the pleasure of swapping it from my 1.5x crop ASP-C sensor Sony Alpha 6300 and seeing what it does on an Alpha 7 Mk. 2, a 35mm full-frame sensor. The good parts about the 40-2 shine, then, with the bokeh in all its glory and color quality becoming even better on a more adept image sensor. If you can help it, I would highly recommend pairing this lens to a full-frame sensor, as that’s what it’s designed for.
After writing the previous sections, I have since purchased an M42 to E-mount speedbooster, to bend back the light rays to be used on my crop sensor 6300. As my adapter now readily makes the 40-2 an APS-C lens and performs exactly like it was mounted on the A7ii. This has produced incredible results, and now with the 40-2 acting like it was designed to I feel so much better about including it in my kit.
To close, the Helios 40-2 is the byproduct of a war, on top of research of the early 1900’s best optical technicians. Somewhat forgotten, you would normally come across this lens being described with the 44-2 in relation to the Biotar design, but really all the lens formula does is achieve this uncanny bokeh. That’s what the Helios 40-2 is best at. It is not easy to get there, however. You get this lens, expect a fight, and the image is your payoff for winning.
In short, I love this thing. I consider it my showstopper, and it’s always in my kit whenever I’m out and about. It takes a lot of getting used to, don’t get me wrong, but once you do, the Helios 40-2 is a one-of-a-kind asset to have along for the strange situations it can open itself up to capture. It’s not the best for every situation, and indeed there are average environments where it struggles, and in a twist of fate, that’s part of the charm. The fact that the 40-2 is such a beast to work with makes the shots you do get that much more artful, and that much more worth it. You can get shots no one else can, in a way no one else can.
What sets apart the Helios 40-2 from any other lens is the unique, identifiable signature of its use. The bokeh, the handling, and its history all add up to what is truly an art. It will not be kind to you if you do not wise up to how to handle it best, for there is a definitive way to use it. I daresay it is like the
It’s going to be my favorite piece of glass for a very, very long time.
(1) Kingslake, Rudolf (1989). A History of the Photographic Lens. Boston: Academic Press. ISBN 978-0124086401, pp. 117–118.
(2) US Patent 583,336, Paul Rudolph, “Objective Glass”, issued May 25, 1897.
(3) The Taylor Hobson Story on Taylor Hobson official website Archived 12 October 2013 at the Wayback Machine.
(4) U.S. Patent 2,019,985 issued Dec 26, 1930.
(5) Dr. J. Kämmerer “When is it advisable to improve the quality of camera lenses?” Excerpt from a lecture given during the Optics & Photography Symposium, Les Baux, 1979″ (PDF). Archived from the original (PDF) on 2015-04-02. Retrieved 12/10/2018.
(6) Herbert Keppler, “Inside Straight: Optical Miracle: The amazing story of the Biotar,” pp. 32–33. Popular Photography & Imaging, Volume 71 Number 5; May 2007. ISSN 1542-0337.
(7) Nogin P.A. “Photographic lens” Moscow, 1961.
(8) “GOI: LENS Catalog 1970. Part 1” Yakovlev A. f., D. Volosov.
(9) V. A. Panov. “The Handbook of the Designer of Optical-Mechanical Instruments”, ed. 3, Leningrad, 1980.
(10) Helios 40-2 85/1.5: “Questions of ergonomics, operation and maintenance.”
Additional Sources not Cited
Volosov D.S. “Photographic Optics” ed. 2, Moscow, 1978.
“PHOTO-CINEMA-TECHNICS encyclopedia”, ed. Iofis E. A., Moscow, 1981.
“GOI: Catalog of LENSES 1971. Part 2” Yakovlev A. f., Volosov D.S.
Slusarev G. G. “Calculation of optical systems”, Leningrad, 1975.
Rusinov M.M. “Technical Optics”, Leningrad, 1979.
“High temperature glass melt property database for process modeling”; Eds.: Thomas P. Seward III and Terese Vascott; The American Ceramic Society, Westerville, Ohio, 2005, ISBN 1-57498-225-7.
Lishnevskaya, E.B. Album “Photographic and projection lenses developed at GOI”, L., GOI, 1963.
Okatov M. A. “Technician’s Handbook for Optics”, St. Petersburg, 2004.
Sokolsky “Tolerances and Optical Image Quality”, Leningrad, 1989.
“Handbook for Cinema Operators” Cherkasov Yu.P. 2, Moscow, 1988.
Carl Zeiss SLR Lenses – Planar T* 1,4/50; [zeiss.com/corporate/int/home.html] retrieved 12/10/2018.
Zenit Camera Catalog, [http://www.zenitcamera.com/catalog/lenseslist.html] retrieved 12/10/2018.
“History of Shvabe Holdings”, translated from Russian, [http://shvabe.com/about/company/krasnogorskiy-zavod-im-s-a-zvereva/historiya/] retrieved 12/10/2018.
“Russian Lenses: Lens Group Helios”, translated from German, [http://www.baierfoto.de/russobj/objektive/helios.html] retrieved 12/12/2018
Mechelhoff, Frank. “Early High-Intensity Lenses”, translated from German, [http://www.klassik-cameras.de/Biotar.html] retrieved 12/12/2018.