analog-digital: what does it mean?

The pair of contrasting concepts is now the standard way to describe the difference between silver-halide processes and the computational processes inside the solid-state equipped modern cameras. The advantage of this pair is clarity: you know what you are talking about, they are easily used and nobody will be confused when you are referring to one or the other. What is not clear, is the exact content of the concepts, especially when applied to the alternative and complementary photographic processes.
For a long time I have wondered what an analog photographic process is. The description and analysis of silver-halide processes since the early 1840s do not use the word 'analog'. The few recent books about silver-halide processing (Haist, Modern Photographic Processes and Tadaaki, Photographic Sensitivity) do not use the word 'anaog' at all.
First of all: the word is traditionally spelled as 'analogue'. American writers drop the silent -ue. 'Analog' is now routinely used in relation with electronics and 'analogue' is used in the sense that someting bears an analogy to somethinge else. An analogy is a similarity between two things that are otherwise dissimilar. The word 'analogy' derivers frome Greek word meaning 'proportionate' and this is correct.
There are two domains where the analog-digital pair is used: the computer industry and the signal-processing industry.
Analogue is related to analogy and this concept is used in the construction of scientific theories. When a scientist has a number of experimental data and wants to give an explanation of what is happening, a model or analogy with familiar events or objects is often introduced. The main definition of ‘analog’ originated in the computer industry. An analog computer represented data in a way that reflects the properties of the data being modelled. Data and numbers may be represented by physical quantities such as electric voltage levels. Analogue computing is primarily a modelling technology. An analogue computer contains shafts, wheels, discs and gears to perform operations and also used relays and vacuum tubes. All this gear was used to simulate and model some physical process in reality. Physical processes can be described mathematically with differential equations and this type of functions can be simulated with analogue computers.
The calculations based on analogue computers that use proportions to simulate and compare processes have a finite accuracy. The newer development of digital computers could increase the accuracy by using a long string of binary digits and were also more reliable. Originally there was no word for the type of computers used for simulation and equation solving. They were just 'computers'. When the digital computer was introduced, a new name 'analogue computers' was given to the modelling type, because analogy was the method that was used to model, calculate and simulate processes happening in the real physical world.
Analogue and digital in the computing world are not alternatives but complementary techniques.

These two parallel themes of calculation and modelling have to be separated when discussing the concepts of analogies, simulations and modelling.
The study of the process of silver-halide photography reveals that there is no computing involved and hardly any simulation or modelling. The characterization of the silver-halide process as analogue is false from whatever angle it is approached.
In the photographic world the interpretation of the two words (analog and digital) is derived from a definition used in electric signal processing. An analog signal is a continuous signal which represents physical measurements. The signal is represented by sine waves and the values of the measurements are mathematically continuous. A digital signal is a discrete time signal generated by digital modulation. The signal is denoted by square waves and the values of the measurements are mathematically discontinuous (or discrete). In order to input these values into a computer the values are converted to digital strings of zeros and ones. The analog signal is concerned with small fluctuations that are meaningful, whereas the digital signal uses large electric charges or voltages.
This description is valid for signal processing and the charge-coupled devices used for the capture, transmittance and storage of electrical signals. A modern photographic camera, equipped with charge-coupled devices, is in fact a powerful computer that processes data in binary format.
A series of MOS capacitors that transport and store electric voltages or currents is called a charge-coupled device and when the voltages or currents (the charge packets) are linked to photon counting or imaging, the device is called an imager. The best description of a ‘digital’ camera would be a camera equipped with an imager.
To describe a camera as digital when inside the camera metal-oxide semiconductor capacitors do the work is an obvious, but narrow-minded approach.

The word ‘digital’ has become magical. When the inside working of a device is based on digital technology it is good, reliable and cheap. The original analog devices are forgotten. All analogue technology is based upon the idea that the magnitude of an electric current or voltage has to be analogous to something in the real world. The bad point is that every electric circuit has a certain randomness, a noise effect that mingles with the analog signal values to produce an uncertainty. Analog signals are small, noise-laden voltages. The new idea is to go from small voltages to large ones: a high voltage is interpreted as one, a low voltage as zero. This one-zero concept was already used to represent numbers in computers and this concept was therefore called ‘digital’. Now the code patterns can describe everything and he strength of the signal is no longer important, The code pattern becomes a non-physical entity. We already had such a system in the past: the telegraph system where time plays an important part: the sequence of long and short intervals between the clicks of the telegraph mechanism.
The technology that is used inside a digital camera is the solid-state imaging that is possible with these charge-coupled devices.
Looking in the most recent brochures about the Canon EOS-1V and the Nikon F4, thee is no mention of the analogue processes and of analog cameras. These models are simply called cameras, very advanced and full of electronics of course, but just cameras. There is some mention of opto-mechatronics technology, but that is all there is to say. It is the analogous situation with the early computers. Before the introduction of the digital computer no one knew or was interested to describe such a computer as analogue.
The digital camera has the same functions and the same type of microcontrollers and printed circuits (Canon boasts that the EOS-1V has lots of 32 bits CPU's) and even the same functionality as these older cameras. The only difference is the fact that the F4 and 1V have to be loaded with film and that the modern EOS-1Dx and Nikon D5 are equipped with solid-state imagers.
The most obvious way to distinguish these two types (film using and imager equipped) would be to use a description such as: cameras using film and cameras fitted with imagers). If a shorter description would be needed the word 'film camera' is not smart, because of the fact that movie cameras also are described as film cameras or cinema cameras. This is confusing. Analogue and digital cameras is also not a smart idea, because of the connection to computations. Inside a digital camera lots of computations take place, but there is no computation at all in the silver-halide photography. When we could agree that silver-halide is the core technology of photography, we might say that we have two types of cameras: photographic cameras and computational cameras. Such a description is more to the point of the core processes inside the camera. A camera is a technological and physical artefact, not a digital or analogue one.
Perhaps I am to nitpicking to question the time-honored description, sanctioned by industry and all photographers in the world. Adoption and conciseness is one side of the medal:a clear description of the technology involved is another one. Given the fact that 'analogue' is associated with archaic, dinosaur and Luddite, and 'digital' with modern, progress and future, it makes sense to return to the roots and find the origin of words and why they are used so falsely in technological discussions about photography.

David Douglas Duncan died on June 7, 2018


DDD as he was known, was one of the last and perhaps greatest photojournalist of the twentieth century. He was the equal of Margaret Bourke-White, Alfred Eisenstaedt, Eugene Smith. He died 102 years old and gave away all his possessions a few years before 2008, living in a French villa at a hill overseeing Cannes.
Some of his possessions were a handful of Leica cameras. He became famous within the photographic world because he selected the newly discovered Nikkor lenses above the Leitz designs. He presumably had the Nikkor lens mounts adapted for his Leica cameras. The content of his pictures were less important than this technical detail. He was however a photographer of the old school who was more interested in taking pictures than talking technically or artistically about them. His pictures were grainy and gritty, probably made with Kodak Tri-X pushed to the limit.
His selection of the Nikkor lenses was a topic of high importance. When a working photographer of his standing threw away the Leitz designs, there must be a garin of truth. Crawley claimed that the Japanese optical designers favoured a high contrast at low frequencies, where as the German counterparts favoured the low contrast at high frequencies, because this was better suited to the new colour films with the finely graded colour hues.
Most Zeiss MTF measurements of older Japanese lenses indicate that this conclusion is not correct: the older Japanese lenses show a low contrast at low frequencies and an even lower contrast at high frequencies. It might be the case that Japanese designs had a (relatively) high contrast at the medium frequencies, precisely where the Kodak Tri-X emulsion showed its best performance.
It is an intriguing problem. The historical discussion indicates that the eye is easily fooled and that the MTF values do not show the proper optical performance the human brain appreciates.

M8 parts and weights

In a hardly known broschure about the virtues of the Leica M8, there is a listing of all components inside the camera body with the weights. This is done to indicate how agile the M8 is. This particular model, completely forgotten by the worldwide Leica community and the company(!), is still a very pleasant camera to use. The high ISO values are quite daring to use, but at speeds from IS O160 (the basic speed of the original Kodak Ektachrome) to ISO 640 (the upper limit of Kodak Tri-X) the printed photographs are excellent.
Here is a partial listing with weights in grams (in brackets):
Display (14); sensor board (10); shutter blades (1); shutter chassis (18); back body part (26); front body part (45); bayonet ring (14); top cover (76); bottom cover (49); rangefinder frame (31); rangefinder prisms (19); screws (1); synthetic leather coating (13); gears-steel (2); gears brass (2); electrical motor (12);

Leica in the twentyfirst century

When I think about the status and current practices of (Leica) photography in the twenty-first C I wish to reflect on
(1) the fluid borderline between the art photograph and the domestic photograph;
(2) the vanishing of the silver-halide photography (influenced by the so-called digital turn) and the disappearance of photography as a distinct social and technical activity;
(3) the status of the Leica camera as the premium precision engineered instrument.

These three topics are related, but are not the only ones that are tangent to the Leica world. Many books have been written about the Leica camera. Most fall in one of three different classes: the history books discussing the evolution of the Leitz Werke and later Leica AG; the collector books, discussing every variant of the camera models that were and are manufactured by the company and the picture books that explain the evolution of the art of Leica photography, beginning with Wolff, and then in orderly succession move on from the French Humanist photographers to the American snapshot-aesthetic street photographers. Now it is quiet in the photographic art world. In the current post-modern art world digital cameras are used to create large tableaus for exhibition purposes in museums and galleries. The Leica digital camera is hardly used by modern large scale and large format art photographers.
The Leica camera is an excellent tool for the spontaneous and instantaneous style of photography. Barnack designed the camera with this goal in mind: a handy-sized pocketable camera of high quality for recording everyday life. This goal matched seamlessly with the trend of the times: modernism as a movement was initiated already in the middle of the nineteenth century (by the writer-critic Baudelaire) to become the major movement in the first part of the twentieth century. Modernism refocused the attention on everyday events in an urban environment and admired the technological progress (1).
The Leica Company has always emphasised the close connection between the Leica and photographic art. This connection has been accentuated presumably to elevate the status of the camera from a high performance compact amateur tool for candid photographs to a tool for the ambitious photographer who wants to follow the great masters of Leica photography. It is significant that Leica now selects photographers that were famous in the second half of the twentieth century when the film-loading Leica rangefinder was the only choice for serious photographers.
Most photographs made with a Leica fall into the category of snapshots. This type of pictures is hardly exciting and is therefore neglected by most art historians and theorists. Recently a turning point has been reached. The academic and art worlds have caught sight of the amateur snapshot as a social, ethnographic and photographic artefact.
The Leica camera was designed as a candid camera and its mechanical and optical qualities were specified to ensure enlargements that could equal the image quality of the ubiquitous 9 x 12 cm or 13 x 18 cm print formats. The accuracy of the manufacture of the camera matched these requirements. The all-metal body was an innovation. The manufacturing technology of that period could guarantee the accuracy of the parts when metal was used. It was the preferred technology of the Leitz Werke as a manufacturer of a wide variety of optical precision instruments. When manufacturing technology progressed and more materials became available, the Leica camera also improved. The well-known editor of the BJP, Crawley, noted that “the quality of manufacture […] improved steadily until […] the manufacturing standard emerged from an ad hoc but workaday mechanism to within sight of a standard to which the term ‘precision’ might be applicable. “
The copies of the Reid and Canon cameras were made to a higher standard of manufacture and were a major impetus for Leitz to produce the Leica M3. In the 1950s and 1960s amateur photography became a widespread activity. The camera industry responded with a tide of innovative products. Most of them were labelled as “built with precision”, “designed by exerts” and a host of comparable phrases. True or not, the amateur photographer did not want to be seen without ‘serious stuff’. One of the most serious kits was the Leica rangefinder system. The optical and mechanical quality justified its status as the professional workhorse for available-light photography. Intriguing is the contrast between the general use of the Leica CRF and its capabilities as a high performing picture engine. Looked at the matter with a purely functional eye, there is no reason to buy a Leica CRF unless you need the reliability and durability of the instrument. Most amateur photographers are very conscious of the value of the Leica camera and use it with care. There is no sound (photographical and functional) argument for the choice of a Leica CRF when taking pictures in the candid snapshot style. The redoubtable Canon RF system would suffice! There are in fact only two or three arguments for investing in the Leica system. One is the very simple argument that the owner wants to differentiate himself from the rest and the other argument is the appreciation for the asceticism of the perfected camera, which is just a camera and not an electronic machine. It is indeed significant that the most discussed properties of the Leica camera are the mythical properties of optical excellence, carefully selected material and meticulously produced parts that are assembled by an experienced workforce. The comparison of the optical performance of the many lens es in the system (its boke(h), its wide open performance, colour correction and so on) initiates always a lengthy discussion on any internet blog or forum. The well-known discussion about the material of the top cover (zinc or bronze) is a good example of the focus of many owners of Leica equipment. Next to the question what is the best lens is the topic what is the best camera. This display of knowledge of camera lore is a harmless and sometimes amusing exercise. It does distract from a serious and honest appraisal of the technical and functional characteristics of the Leica CRF. In this respect we find the third reason for the choice for the Leica CRF system: the compact high performance lenses and the mechanical-manual operation of the camera and its attached lens. The amount of detail that can be accurately recorded by the Leica CRF is one of the big assets. The manual operation is a vivid reminder of the materiality of the photographic process, especially when using and processing silver-halide emulsions.
One of the great assets of the Leica CRF system is the small size and limited weight of many M lenses while preserving a very high image quality. With the new introductions Leica seems to have changed their strategy: several new lenses for the M-system break a barrier. One of the main complaints of the old Zeiss Contarex was the fact that the lenses for this system were designed without any regard for size and weight. The Zeiss Otus lens is the first modern design that also disregards size and weight. At first this design was negatively reviewed because of these physical characteristics. Now the new designs for the CL and SL cameras are bulky too (their performance is not disputed). The CL and SL indicate that the Leica designers follow the standard of the day: industrially-sized bodies with every possible option integrated into the body and fast but bulky AF lenses with a variable range of focal lengths. This is the current standard in a digital Coca-Cola world. The camera with a different approach that distinguishes itself from the mainstream is the Leica M CRF.
There are several remarkable antinomies in the argumentation around a Leica camera, solid-state equipped or cartridge-loading. Here floods a list, certainly not complete:
(1) The choice of materials of a solid-state equipped camera ensures a prolonged durability, but the pace of technology and the demands of the marker require a continuous refreshment of the camera models. This relatively fast product cycle causes a drop in value and popularity. The M8.2 is still a very good camera for most purposes that the Leica photographer will strive for. The popularity of this particular model is very low now. The risks of break down and a scarcity of repair parts does not bode well for a prospective owner. Compare this state of affairs with the situation for the Leica M4: this one can be repaired by any competent repairperson and there is an abundance of spare parts.
(2) The insistence by all buyers of a Leica camera that it should deliver the highest possible image quality is at odds with the modest demands for the final result. The so-called pixel peepers use a ridiculous process to examine the properties of a virtual image file.
(3) Many older users of the Leica CRF complain about a reduced ability for accurate focus with the manually operated rangefinder and switch to one of the autofocus models. At the same time the subjects of the photographer are in many cases static, a condition that does not require fast and accurate autofocus. The photographers who use a Leica rangefinder camera had and have zone focusing, attentive observation and a host of other methods at their disposal to cope with fast changing situations.
(4) A comparable argument can be set up for the automatic exposure mechanism that is available since the M7. Many commentators in books and on the internet state that AE is needed to ‘get the results’. On the contrary: an external handheld exposure meter suffices to measure the ambient light and experience can change the settings. In open air there is a stable illuminance value between 11.00 and 15.00 hours.
This list of purely photographic problems and how to cope with them is an indication that photographers now have lost their traditional grasp of the technical matters. The ubiquitous software algorithm is the root of this situation. The efficiency of the processing of the numerical data (after the analog-digital converter has transformed the analog data into numerical ones) ensures that almost every fault of the user is compensated and supports the user when knowledge or experience of the photographic process is lacking. The downside of this reliance on unknown processing algorithms is the dependence of the user on the choices and ideas of the software developer inside the company. With chemical materials the user knows exactly what is going on and how the processes can be handled to get the desired results: the Zone System is an excellent example of the controlled manipulation of the photographic process.
The hallmark of the Leica camera is the accuracy of the manufacture. The literature of the Leica company refers often to this characteristic. The most used examples are however the taken from the optical design and manufacture. In this domain the tolerances are indeed small (0.001 mm are common). The manual assembly of elements with such narrow tolerances is not simple and requires highly trained and gifted workers with a sensitive tactile feeling. Some workers are indeed capable of handling such narrow tolerances.
The manufacture and assembly of the camera body is a different story. The adjustment of the sensor surface alignment and distance from flange to surface is computer-assisted. It depends however on the worker how to handle the upper and lower tolerances.
The purely mechanical parts are manufactured to a tolerance of 0.01 mm (now: it was 0.02 mm). As said, the tolerance level can be held (now and in the past) to very narrow limits when the whole process is competently monitored and verified. There are several levels of precision.
The first is micro-precision: workpiece accuracies below 10 microns. The second is ultra-precision: workpiece accuracies lower than 3 microns. The third is nano-precision: workpiece accuracies below 1 micron. Camera products fall in category one and optical products fall in category two. In the world of machine shops, levels one and two are normal practice and easily achieved. The claim that Leica products can be designated as high-precision might be true, but the claim should be supported by actual numbers. It is too simple to state the claim and let the visitors of the factory be impressed without factual evidence (this happens a lot, alas! And not only when doing a factory visit at the Leica Company in Wetzlar).
It is a common response in the industry of camera manufacture to state that the publication of standards of manufacture and the tolerances used during machining and assembly are secret because of its sensitivity of such figures. There are however three aspects to discuss in this respect: the specified tolerance levels by the design and engineering department.; the actual tolerance levels in the machine shop and assembly process (including the measuring tools and the competence of handling them) and the measuring of the tolerances at the final control.
It is a curious paradox that the accuracy of manufacture and assembly increases at the same time that the effectiveness of the digital processing of image data would allow a lowering of the manufacturing standard. The Leica products have always distinguished themselves by the (high-)precision of engineering and manufacturing, because this characteristic is supposed to be a unique selling point.
This level of manufacturing accuracy is appropriate for the film-loading cameras because the silver-halide processing chain follows a pattern of stepwise degradation of image quality. The digital processing workflow on the other hand has at every step the potential of an improvement of image quality.

The disappearance of photography as a distinct social and technical activity is a fact now that the modern visual culture is omnipresent and has absorbed photography as only one of many producers of imagery. Everyone takes photographs at every moment of everything and uploads them to one of the social media on the internet. Billions of pictures are taken every week (perhaps every day, no one knows exactly). The content of these pictures is not distinguishable from what can be seen in the classic family album. Photography as a process is inherently amateurish and it shows! Photography as a craft may be classified now as one of the disappearing old-school trades. The discussion on the forums and in the magazines is as traditional and conventional as ever. The embracement of the digital technology has not liberated the user. Fifty years ago the most discussed questions were: what film to use, what camera, what lens for best imagery, for portraits and so on. Now the questions have hardly changed. What film to use has been exchanged for what sensor to use, how many pixels do I need, but the questions about cameras and lenses are still the same. Everybody has its preferences now and in the past. The Pentax promoters are as active as the Nikon, Olympus, Panasonic, Fuji, Canon or Leica promoters. Only a very few persons dare to propose that photography has nothing to do with the equipment and everything with the subject and with what happens in the brain of the photographer.


M7 discussion continued

It is quite remarkable how much noise the notification about the Leica M7 makes in the photographic world. The aperture priority exposure automation of the M7 was a first for the Leica M. Till 2002 everybody had to cope with the M6 method: balancing two LEDs by shifting manually aperture and/or shutter speed. In those days it was referred to as pure photography: learning the basics of exposure metering was a must for any novice in the craft. The method pioneered in the Leica M7 is still the exposure method of the M8 to M10. There is no other option if we accept that the lenses have to be handled manuaally and the camera has no electric or mechanical connection to inform the internal microprocessor of the selected aperture and adjust the shutter speed accordingly or the other wy around. What Leica accomplished was standard procedure for all Japanese manufacturers of that time. But Leica was limited in its options because of the manufacturing process and the choice of the mechanically governed horizontally running cloth focal plane shutter.
The fact that silver-halide afficionados within the Leica world select the MP and M-A as their primary tool speaks volumes for the trends: the film community wants a basic camera without any automation (one cannot seriously call the M6 metering system an advanced version of camera automation). The digital community (a much larger segment of the Leica camera buyers) wants as much automation as possible: even the M10 is not enough and there is a tendency for Leica CRF owners to buy a CL or SL to make life easier, but also adds to the weight and volume of the camera they have to handle.
Many comments claim that the instantaneous exposure mechamism of the M7 allows them to take pictures that are impossible to take when one has to measure the expusure with the M6 or even the clip-on exposure meter of the M3 to M4-P (excepting the M5 of course). This is nonsense because a scene illumination does not change that fast. You can take one incident light measurement and use this as a reference. The rest is simple guess work based on experience.
The functionality of the M7 is transferred to the functionality of the M10. With the exception of smooth changes of ISO settings, direct control of the picture on the back screen, selective spot metering and focus control on screen, the photographic experience is the same. What is embraced in the digital M cameras is rejected in the cartridge loading bodies.
There are discussions about the question how and why to buy a cartridge loading Leica camera. Mike Johnston on his blog remarks that the M7 is not a purist camera (evading the definiion of what 'purist' is) but that the M7 with the aperture priority AE enables the photographer (him) to take pictures (presumably in a successful way). Then he follows on his traditional mantra (and one joined by many Leica second hand sellers) that the best Leica film camera is the M4 (the one that should be the best mechanical Leica camera with the most elaborate manufacturing processes. (You can read in my new book that this is not the fact!). There are many hyperboles in his blog about the M7 and film Leicas and lenses (the reference to HCB and his Summicron lens is not supported by any factual research). The long list of comments shows an intense interest in the Leica things,but I have to say that not one comment breaks away from the standard and not very illuminating way of discussing the Leica, the rangefinder concept and the conventional film-digital diichotomy. I really miss Susan Sontag and her comments about photography. At least she elevated the discussion to a higher level.
It might be time to break out of the myth culture surrounding the Leica cameras and to discuss the virtues of the Leica CRF in a more sober way.
My view of the cartridge loading cameras: buy a new M-A (a good original M3 is difficult to find and the modern manufacturing processes, including material choices are now much improved). OR buy a second hand M4-P (the 75 mm frame is very useful) or any one the many M6 bodies on the market. If you are new to Leica and want to experience the digital path buy an M8.2. It hs its problems but coping with them is a very rewarding experience. It makes sense to limit yourself to ISO 640.

© 2005-2018 Erwin Puts Contact Me