What is a “normal” lens anyway?

A “normal lens” for a 35mm camera, either film or digital generally refers to a lens with a focal length of 50mm. When you look through the viewfinder of a camera with a 50mm lens attached, the scene looks about the same as it does with the naked eye. Although a 50mm focal length is considered to be a normal lens for a 35mm film or DSLR camera, the same could not be said for all other formats. That’s why you don’t see a lot of 50mm lenses for Micro-Four-Thirds (MFT). A 50mm lens on MFT behaves likes a 100mm full-frame lens, because of the crop-factor, or basically because the sensor size is smaller. Of course “normal” lenses on a 35mm format camera are not exactly pigeonholed into a single focal length, instead they range anywhere from 40mm to 60mm (although this too may differ slightly depends on who describes it).

The standard idea has always been that the focal length of a normal lens should be about the same as that of the diagonal of the film frame/sensor, i.e. the measured distance from one corner of a negative’s frame to the corner diagonally opposite, in millimetres. For example the diagonal of a 36×24mm full-frame is 43mm (although most SLR cameras use a 50mm lanes as “normal”). Even other formats don’t hold true to this mathematical idea. The Olympus PEN F, half-frame camera should have a standard lens of 30mm, however the three lenses offered are instead the 38, 40, and 42mm, equivalent to 55/58/60mm (on a 35mm camera) respectively (there were also 25mm lenses, but they were considered wide angle).

Every different sized sensor has it’s own “normal” lens. Here is a list of normal focal lengths (FL) for various film/sensor sizes (D=digital; F=film), based on commonly used lenses for each system:

FormatDimensions (mm) H×WDiagonal (mm)Normal lens (mm)
16mm cine (F)7.5×10.312.725
Micro-Four-Thirds (D)13×17.321.6325
APS-C (D)15.1×22.727.335
Half-frame 35mm (F)24×183028
APS-C (F)16.7×25.130.128 (+30)
35mm film/DSLR (F,D)24×3643.350 (+55, 58)
Medium (D)33×445565
645 (F)56×4271.875
6×6 (F)56×5679.280
6×7 (F)56×6787.3105
5×4 (F)93×118150.2150

Where did the term “full-frame” originate?

Why are digital cameras with sensors the same size as 35mm SLR’s, i.e. 36×24mm, called full-frame cameras? This is somewhat of a strange concept considering that unlike film, where the 35mm dominated the SLR genre, digital cameras did not originate with 35mm film-equivalent sized sensors. In fact for many years, until the release of the first digital SLRs, camera sensors were of the sub-35mm or “crop-sensor” type. It was not until spring 2002 the first full-frame digital SLR appeared, the 6MP Contax Digital N. It was followed shortly after by the 11.1MP Canon EOS-1Ds. It wouldn’t be until 2007 that Nikon offered its first full-frame-camera, the D3. In all likelihood, the appearance of a sensor equivalent in size to 35mm film was in part because the industry wished to maintain the existing standard, allowing the use of standard lenses, and the existing 35mm hierarchy.

One of the first occurrences of the term “full-frame” as it related to digital, may have been in the advertising literature for Canon’s EOS-1Ds.

“A full-frame CMOS sensor – manufactured by Canon – with an imaging area of 24 x 36mm, the same dimensions used by full-frame 35mm SLRs. It has 11.1 million effective pixels with a maximum resolution of 4,064 x 2,704 pixels.”

Canon EOS-1Ds User Manual, 2002

By the mid 2000’s digital cameras using “crop-sensors” like APS-C had become standard, but the rise of 35mm DSLRs may have triggered a need to re-align the market place towards the legacy of 35mm film. As most early digital cameras used sensors that were smaller than 36×24mm, the term “full-frame” was likely used to differentiate it from smaller sized sensors. But the term has other connotations.

  • It is used in the context of fish-eye lenses to denote an image which covered the full 35mm film frame, as opposed to fish-eye lenses which just manifested as a circle.
  • It is used to denote the use of the entire film frame. For example when film APS-C appeared in 1996, the cameras were able to take a number of differing formats: C, H, and P. H is considered the “full-frame” format with a 9:16 aspect ratio, while P is the panoramic format (1:3), and C the classic 35mm aspect ratio (2:3).

In any case, the term “full-frame” is intrinsically linked to the format of 35mm film cameras. The question is whether or not this term is even relevant anymore?

The whole full-frame “equivalence” thing

There is a lot of talk on the internet about the “equivalency” of crop-sensors relative to full-frame sensors – often in an attempt to somehow rationalize things in the context of the ubiquitous 35mm film frame size (36×24mm). Usually equivalence involves the use of the cringe-worthy “crop-factor”, which is just a numeric value which compares the dimensions of one sensor against those of another. For example a camera with an APS-C sensor, e.g. Fuji-X, has a sensor size of 23.5×15.6mm which when compared with a full-frame (FF) sensor gives a crop-factor of approximately 1.5. The crop-factor is calculated by dividing the diagonal of the FF sensor by that of the crop-sensor, in the case of the example 43.42/28.21 = 1.53.

Fig.1: Relative sensor sizes and associated crop-factors.

Easy right? But this only really only matters if you want to know what the full-frame equivalent of a crop-sensor lens is. For example a 35mm lens has an angle of view of rough 37° (horizontal). If you want to compare this to a full-frame lens, you can multiply this by the crop-factor for APS-C sensors, so 35×1.5≈52.5mm. So an APS-C 35mm lens has a full-frame equivalency of 52.5mm which can be rounded to 50mm, the closest full-frame equivalent lens. Another reason equivalency might be important is perhaps you want to take similar looking photographs with two different cameras, i.e. two cameras with differing sensor sizes.

But these are the only real contexts where it is important – regardless of the sensor size, if you are not interested in comparing the sensor to that of a full-frame camera, equivalencies don’t matter. But what does equivalence mean? Well it has a number of contexts. Firstly there is the most commonly used situation – focal-length equivalence. This is most commonly used to relate how a lens attached to a crop-sensor camera behaves in terms of a full-frame sensor. It can be derived using the following equation:

Equivalent-FL = focal-length × crop-factor

The crop-factor in any case is more of a differential-factor which can be used to compare lenses on different sized sensors. Figure 2 illustrates two different systems with different sensor sizes, with two lenses that have an identical angle of view. To achieve the same angle of view on differently sized sensors, a different focal length is needed. A 25mm lens on a MFT sensor with a crop-factor of 2.0 gives the equivalent angle of view as a 50mm lens on a full-frame sensor.

Fig.2: Focal-length equivalence (AOV) between a Micro-Four-Thirds, and a full-frame sensor.

Focal length equivalency really just describes how a lens will behave on different sized sensors, with respect to angle-of-view (AOV). For example the image below illustrates the AOV photograph obtained when using a 24mm lens on three different sensors. A 24mm lens used on an APS-C sensor would produce an image equivalent to a full-frame 35mm lens, and the same lens used on a MFT sensor would produce an image equivalent to a full-frame 50mm lens.

Fig.3: The view of a 24mm lens on three different sensors.

When comparing a crop-sensor camera directly against a FF camera, in the context of reproducing a particular photograph, two other equivalencies come into play. The first is aperture equivalence. An aperture is just the size of the hole in the lens diaphragm that allows light to pass through. For example an aperture of f/1.4 on a 50mm lens means a maximum aperture size of 50mm/1.4 = 35.7mm. A 25mm f/1.8 MFT lens will not be equivalent to a 50mm f/1.8mm FF lens because the hole on the FF lens would be larger. To make the lenses equivalent from the perspective of aperture requires multiplying the aperture value by a crop factor:

Equivalent-Aperture = f-number × crop-factor

Figure 4 illustrates this – a 25mm lens used at f/1.4 on a MFT camera would be equivalent to using a 50mm with an aperture of f/2.8 on a full-frame camera.

Fig.4: Aperture equivalence between a 25mm MFT lens, and a 50mm full-frame lens.

The second is ISO equivalence, with a slightly more complication equation:

Equivalent-ISO = ISO × crop-factor²

Therefore a 35mm APS-C lens at f/5.6 and 800 ISO would be equivalent to a 50mm full frame lens at f/8 and 1800 ISO. Below is a sample set of equivalencies:

           Focal Length / F-stop = Aperture ∅ (ISO)
       MFT (×2.0): 25mm / f/2.8 = 8.9mm (200)
     APS-C (×1.5): 35mm / f/3.9 = 8.9mm (355)
Full-frame (×1.0): 50mm / f/5.6 = 8.9mm (800)
      6×6 (×0.55): 90mm / f/10.0 = 9.0mm (2600)

Confused? Yes, and so are many people. None of this is really that important, except to understand how a lens behaves will be different depending on the size of the sensor in the camera it is used on. Sometimes, focal-length equivalence isn’t even possible. There are full-frame lenses that just don’t have a cropped equivalent. For example a Sigma 14mm f/1.8 would need an APS-C equivalent of 9mm f/1.2, or a MFT equivalent of 7mm f/0.9. The bottom line is that if you only photography using a camera with an APS-C sensor, then how a 50mm lens behaves on that camera should be all that matters.

Now that’s a camera!

An 8×10 still camera operated by photographer Neal Harburger used to capture stills on Paramount westerns c.1930s. The camera was a Minex, designed by A. Adams & Co. of London. The camera was 18 inches high, 30 inches long (with the bellows extended) and weighed 34 pounds. From the literature it looks to be the “Tropical” model made of brass, teak, and Russian leather bellows.

Ultrafast lenses – the Noctilux 50mm f/1

After Canon and Nikon gave up on their sub-f/1.1 lenses, there was a lull for a while. In all possibility it was likely considered that film would just get so fast there would be little need for these light behemoths. But high ISO film was only introduced in the mid to late 1970s – Fujicolor 400 (1976), Kodakcolor 400 (1977). Indeed faster films begat faster lenses.

The Leitz 50mm Noctilux f/1 for Leica M cameras appeared in 1976, designed by Walter Mandler (1922-2005) and produced by Ernst Leitz Canada. It was a successor to the earlier Noctilux f/1.2. Bob Schwalberg reviewed the lens in 1976 [1]. His observation was that it had a high optical contrast and almost no flare at f/1, “outimaging” its compatriots the Noctilux f/1.2 and the Summilux f/1.4.

The lens was manufactured for a long time, from 1976-2007. The name Noctilux, was designated for three lenses with differing apertures:

  • Leitz Noctilux 50mm f/1.2 aspherical (1966-1976).
  • Leitz/Leica Noctilux-M 50mm f/1.0 (1976-2007).
  • Leica Noctilux 50mm f/0.95/50mm ASPH (2008- )

The lens was constructed using only spherical curvatures, as opposed to the f/1.2 which used two aspherical surfaces with a 6/4 design. The earlier design was likely changed because the aspherical lenses were too expensive to manufacture. The f/1 uses a modified Gauss design of seven elements in six groups with an “air-lens” between the second and third elements. The second and fifth elements were made using Noctilux 900403 glass. The 1st, 6th, and 7th elements were made with Lanthanum glass (LaK12, LaF21). The 900403 glass, developed at the Leitz Glass Laboratory had a higher zirconium oxide content giving it a refractive index of 1.9005 and a dispersion value of 40. (This glass had a melting point of 1600°C, and had to be cooled in a controlled manner over 10-12 days).

But it was no light lens. It was 63mm in diameter, and weighed about 600g. It still suffered from the one thing all ultrafast lenses suffer from – a narrow DOF (2” at 5 feet). When released it sold for US$855. They now routinely sell for C$8,000-11,000.

References:

  1. Bob Schwalberg, “50-mm Noctilux f/1: Sharpest superspeed lens yet?”, Popular Photography, 78(2), pp. 80,81,105 (1976) Dominique Guebey Jungle, “Leitz Noctilux 50mm f:1.0”

Further reading:

the histogram exposed (v) – indistinct

This series of photographs and their associated histograms covers indistinctly shaped histograms, i.e. images which have a histogram which does not really have any distinct shape.

Histogram 1: Dark depths

This is a good example of a low-key image, but contains content which makes this an aesthetically pleasing image. The histogram shows as asymmetric unimodal, tiered towards the darker tones. The dark tones, ①, are naturally provided by the black hull of the ship, the dark vegetation, and the water. The midtones, ②, are associated with the lighter vegetation, and the ships reflection in the water. The larger of the two peaks in the highlights, ③, is the side of the ship, and the building on-shore, and the smaller one, ④, basically is the white on the front of the ship.

Olympus E-M5II (12MP): 20mm; f/4; 1/160

Histogram 2: Light buildings

This is an excellent example of an image (Bergen, Norway) which has white clipping, but it doesn’t have much to do with blown-out regions. The whites in the image are entirely associated with the sides of the two larger buildings which are exposed to direct sunlight. This is not a distinct multipeak histogram, but it is divided into four tonal zones: ① the shadows; ② the midtones; ③ the upper midtones and highlights; and ④ the whites.The sun was intense on this day leading to a slightly paler sky, and bleached buildings facing into the sun.

Olympus E-M5II (12MP): 17mm; f/5.6; 1/250

Histogram 3: Red train

This image of a train at the station in Voss (Norway) which has a histogram which covers a broad range of tones. The image has good contrast overall with only two distinct peaks: ① Values 87-124 comprise most of the red and dark gray portions of the train, as well as fine detail throughout the image; and ② Values 234-245 comprises the edge of the train roof. Images which contain a lot of detail and varied tones typically produce histograms containing a lot of “spiky” detail.

Olympus E-M5II (12MP): 19mm; f/4.5; 1/200

Shooting photos from an aircraft

Taking photos from a train is not that hard. Taking photos from the window of a plane is trickier for a number of reasons. Firstly, you can’t really wander the aisles of a plane looking for the best vantage point, and secondly, there are very few good photos to be had at 35,000 feet.

There are of course some technical issues, the biggest one being aircraft windows. Plane windows are technically made up of three panes: (i) an outer pane flush with the outside fuselage, (ii) an inner pane (which has a little hole in it), and (iii) a thinner, non-structural plastic pane called a scratch pane. The scratch pane is the part passengers can touch, and inadvertently scratch. And the windows are not made of glass, but rather a type of plexiglass known as “stretched acrylic” (the flight deck windshields are made with glass-faced acrylic). These windows are not ideal to look through, because they are never perfectly clear.

An aerial view of Laval on approach to Pierre-Elliott Trudeau Int. Airport in Montreal. Taken from a De Havilland Canada Dash 8 aircraft which was banking. iPhone 5 (4.12mm; f/2.4; 1/531).

Second is the aircraft itself. In smaller planes windows are often located closer to the centre-line of the plane, so views of the ground are better. The larger the plane, the higher up the windows are on the aircraft’s curved fuselage (largely due to the cargo space below).

Example vertical angles of view for a 35mm lens on an APS-C camera on different aircraft.

Here are some tips for shooting photographs from a plane:

⦿ Plan ahead − This means studying the route – what scenic sites will you be passing over? For example the Icelandair flight from Toronto to Keflavik (ICE604) typically flies over southern Greenland, around 5am (local time) – which from May to August is around sunrise. Sunrise and sunset are great times to try and take a shot – shots of cloud and sky by themselves aren’t exactly inspiring. It might also be good to check weather conditions along the route.

⦿ Choose a seat − With the route and time of day in mind, decide on where you want your window seat. Sitting on the wrong side of the plane at the wrong time of day, might result in you shooting into the glare of the sun. Use an airline seat map to help guide your choice, noting that the type of plane will make a difference in where you want to sit. Optimally, a seat in the fore or aft of the plane is preferable, avoiding over-the-wing seats. However in a turboprop aircraft the wings are less of an issue because they are typically above the window. In some planes the aft of the wing can be problematic because of jet exhaust blurring parts of the image.

⦿ Select an appropriate camera/lens − Smaller is often better when it comes to cameras. So a compact camera, or even smartphones are both good choices because they are both accessible and unobtrusive, and frankly using a DSLR is likely gross overkill. A wide lens is typically best – the longer the lens the more susceptible it is to vibration and turbulence, even with good IBIS. You can experiment with UV and ND filters, but avoid polarizing filters. The plexiglass panel in the window in combination with the polarizing filter actually produces an effect called birefringement, which creates a rainbow effect in an image.

⦿ Make sure the window is clean − Always make sure to clean the scratch pane before take-off – the fewer smudges you have to shoot through the better. The scratch panes may never be perfect, because they tend to take a lot of abuse.

A little bit of art, flying into Montreal. iPhone 5 (4.12mm; f/2.4; 1/343). The lens on the iPhone 5 is roughly equivalent to a 30mm on a full-frame.

⦿ Hold the camera close − You can reduce the effect of scratches etc. by placing the lens as close to the window as possible (but not directly on the window, unless you use a rubber lens hood).

⦿ Choose settings − Faster is better when it comes to shutter speeds, e.g. 1/600 to 1/2000. The further away the object being photographed, the more lenient you can be with shutter speed. A mid-range aperture like f/8 is also quite appropriate – sharpness is all relative when shooting through three panels of plexiglass. If using a smartphone cameras, the camera will handle all the settings.

⦿ Use manual focus − Sometimes the window can be a bit hazy, and this can interfere with auto-focus. Switching to manual focus usually works quite well, making sure to focus at infinity.

The best “aerial” photographs come at landing time, or when a plane is close enough to the ground to provide an aerial view. I’ve taken some great photographs of Montreal from a smaller plane, and even on the approach to Keflavik (Iceland). What to photograph? That really depends on whether you want to take some artisanal/experimental shots, or aerial shots of landscapes. Some people like to take pictures of the wings, and that makes a lot of sense given that it helps put some shots into context. The image shown below wouldn’t be that interesting if it weren’t for the plane’s curved wingtip. Clouds are also interesting, particularly if seen from above, as are human incursions on the landscape e.g. farms, and natural wonders like rivers.

Approaching Keflavik, Iceland. iPhone 6s (4.12mm; f/2.2; 1/950).

Aerial shots can be plagued by a aerial haze, which imparts a gray layer on the image. During the day, the shorter wavelengths of light (blues and violets) are scattered by the gasses in the atmosphere. Light is also reflected by particulates in the atmosphere which results in hazy skies. This can be reduced by using a UV filter, or in post-processing. Reflections can also be an issue, especially if it is dark outside – lights within the cabin will reflect back towards the camera from the three sheets of plexiglass. And no flight is smooth – engine vibration, and air turbulence will make it difficult to achieve long exposures.

The original aerial shot of Iceland with a nice layer of gray haze. (iPhone 6s; 4.12mm; f/2.2; 1/999).
The image modified with some contrast stretching, and enhancement of the blue colour channel.

At the end of the day, there is no guarantee for good photographs shooting through a window. There is every chance that some images may be soft, especially around the edges, or condensation/ice may build-up on the window, thwarting an notion of taking “good” pictures. It might be that the plane is shrouded in clouds the whole way through the journey. The best advice is to take lots of photos, and experiment.

Above the clouds (iPhone 6s; 4.12mm; f/2.2; 1/746).

If you are interested in taking photographs from a small plane, such as the tours offered by Sea to Sky Air in Squamish BC, then you will need a few more tips, and I have provided some resources below. For anyone wanting to visit Iceland, check out my post Visiting Iceland? – Beware of the glaciers.

Further reading:

The caveats of travel photography

As amateur photographers, one of the best photographic experiences is taking photographs when travelling. But it’s also often somewhat of a gamble. Sure, those perfect images you see on tourist websites and the like are truly spectacular, but they are usually taken by professional photographers who have the time to wait for the most optimal moment, and often don’t have to contend with masses of people spoiling the vista, or poor weather. Or they are photographs taken from above with a professional drone. But as don’t all have the ability, or the ability to wait all day to take the perfect photograph.

Indeed, there are some pictures you will not be able to duplicate. In many places the best photographs are the ones you can buy, i.e. postcards (doesn’t that seem old fashioned?) or photo books (before leaving Iceland on a visit years ago, I picked up a copy of I Was Here: Iceland, a small photo book by Icelandic photographer Kristján Ingi Einarsson). It’s not surprising that these images are so good, because they are taken using full-frame of medium-frame cameras, and high-resolution drones (with the proper permissions). They are often full of detail, brightly coloured and lack the cars and people that always seem to ruin a shot.

When you are somewhere for a short period of time, you hope you’ll get a good series of photographs, but you can never be sure of that, and it usually has to do with two things – weather and people. People are only a problem in so much as in popular places they are everywhere. It’s sometimes hard to capture a good photograph of something, sans the people. But it’s not insurmountable – go early or late, or I guess post-process it to remove unwanted objects. Weather is more of an issue, especially in places where the weather can change quickly.

The perfect storm – A geysir at the Geysir Hot Springs, an attraction along the Golden Circle in Iceland. But the weather is never guaranteed to be perfect, and there are always a lot of people, making the perfect photograph extremely hard to obtain.

A good example of this is travelling in Iceland. Look at the tourism website and you will see fantastic photographs of the natural landscape. However if you visit, your photography will be largely affected by both the weather and the hoards of tourists at some sites. During the short summer there can be a huge number of tourists, and natural attractions such as those along the Golden Circle are packed to the rafters with tourist buses. Go early or late if you can there is ample daylight until late, and you might avoid the latest if the masses. The weather in Iceland can also turn on a dime, even in the height of summer. Rain and fog are abundant. Weather is always a factor, and not something you can process away. On a summer day, you can experience a sunny day, a windy day, a rainy day or even sometimes unexpectedly, a winter day.

But when the weather gives you lemons, you just have to learn to adjust. You may be in a place you will never return to, and you want to make the most of the time you have. Sometimes this means having the most appropriate gear. A camera and lenses with good weather sealing makes the world of difference in both wet and dry, dusty conditions. An optimal choice of a lens that is good in all circumstances – you don’t really want to be changing lenses too often. Also if venturing off to a place with weather extremes take precautions, like purchasing a camera shell to keep out the rain and dust.

P.S. There is some great drone footage out there of places like Iceland, however with newer regulations it has become harder to actually fly drones in some places. For example in Iceland, flying a drone in national parks, protected areas, nature reserves, and monuments is not permitted. It is becoming stricter in many places, because let’s face it, drones can sometimes be quite annoying.

P.P.S. For a great introduction to Iceland get a copy of Stunning Iceland: The Hedonist’s Guide, by Bertrand Jouanne and Gunnar Freyr (just released this year).

Superfast lenses – the original Noctilux 50mm f/1.2

When it was released in 1966, the Leica Noctilux 50mm f/1.2 was an altogether different animal. It was great at shooting in low light, expensive and difficult to make. That’s probably why less than 2000 were made. By the mid 1960s, there were a number of players in the sub-f/1.4 field, primarily for shooting in low light. Nikon, Canon, and Minolta all had f/1.2 lenses. Work on the use of aspherical elements in lenses began in the late 1950s.

The Noctilux 50mm f/1.2 was produced from 1966 until 1975, and was the worlds first lens to feature aspherical elements. The name Noctilux is a combination of Nocti, which is derived from the word nocturnal, while Lux is Latin for light.

“Even at f/1.2 the NOCTILUX produces so very little flare that strong light-sources are imaged with only minimum halo surround. Brightly back-lighted subjects, anathema to poorly corrected high-aperture lenses, have clear, accurate outlines.” [2]

This was supposedly the first Leitz lens to sacrifice some resolution in order to gain contrast. Bill Pierce who wrote a brief article on the new lens in 1967 remarked: “To the best of my knowledge, rather extensive in this tiny field, none previous to the Noctilux could deliver a clean, biting journalistic image at maximum aperture.” [1]

“Superior optical contrast due to high correction for coma and all other critical aberrations and due to freedom from internal reflections, make the NOCTILUX the ·ideal high-aperture lens for use with high-speed available-light films.” [2]

The first prototypes were made in April of 1964 Designed by Helmut Marx and Paul Sindel (Helmut Marx was Professor Max Berek’s successor as head of the photographic lens design in Wetzlar, and creator of the first Summicron 50 in 1953). The Noctilux 50mm f/1.2 was released in 1966. The Leica Noctilux 50mm f/1.2 is a 6-element Gauss variant with 4 members. It has two aspherical elements (front and rear) which were made on a specially built grinding machine that had to be operated manually. There was only one machine, and only one person capable of operating it (Gerd Bergmann), so many elements had to be discarded as rubbish.

It was sometimes claimed to be the fastest production lens in the world, because other manufacturers lenses often proved to be slower than indicated. After the release in 1966 there was much research to produce an f/1 version of the lens with 3 Aspherical elements, but in 1970 the project was abandoned because the aspherical technology was in its infancy, and the production costs were immense. The f/1.2 lens remained in production until only 1975 with 1757 units produced. A new version of the lens, the Noctilux-M 50mm f/1.2 ASPH was released in 2021, with the construction only minimally changed. The new lens sells at US$7900, which is a bargain considering the old lens can sell for upwards of $US70,000.

References:

  1. Bill Pierce, “Because it was possible”, Popular Photography, 60(1), p.135-156 (1967)
  2. Leica brochure, “50mm NOCTILUX f/1.2

Further reading: