Photography Tutorial

Copyright 2013 by Ronald B. Standler

Table of Contents

    1. Shutter Speed
    2. Aperture
    3. Sensitivity
    4. White Balance
    5. Contrast
Desirable Digital Camera Features
Comparing Film to Digital
    1. Spatial Resolution
    2. Dynamic Range
    3. Sensitivity
    4. Cost
    5. Digital has no chemistry
    6. Storage
    7. Duplication


In 1971, I taught myself to develop and print black & white film, as part of my scientific research in lightning and electrical discharges in gases. In Feb 1973, I purchased a Nikkormat camera body and Nikkor lenses with focal lengths of 28 mm (wide-angle) and 135 mm (telephoto). I used the wide angle lens for photographing atmospheric optical phenomena (e.g., rainbows, halos) in New Mexico. I used the telephoto lens for photographing nocturnal lightning in distant thunderstorms, as well as documenting my experiments.

In 1983, I upgraded my camera body to a Nikon FM2. During 1984-1993, I mostly used my camera to prepare slides to illustrate my lectures during presentations at electrical engineering symposia.

In May 2001, I purchased my first digital camera, a Sony that wrote files to a floppy disk. In Oct 2010, I replaced the Sony camera with a Canon SX130.

In Oct 2012, I purchased a Nikon D7000 digital camera body to use with my collection of manual-focus Nikkor lenses I had purchased during 1973-1990. I now use my cameras mostly for forensic photography, but I sometimes photograph old buildings to preserve history.

The information in this essay emphasizes a single-lens reflex (SLR) camera for 35 mm film and the more modern digital cameras that use similar lenses. Some of the numerical values in this essay are not valid for cameras that use 100 × 125 mm sheet film, or larger formats.


There are two ways to regulate the amount of light that reaches the film or digital sensor in a camera: (1) shutter speed and (2) lens aperture.

1. Shutter Speed

There is a series of preferred values of shutter speed used in all cameras. The preferred values are generated by doubling from 1/1000 second:
1/1000, 1/500, 1/250, 1/125, 1/60, /1/30, 1/15, ...
(These numbers would be simpler if expressed in milliseconds, but traditionally they are expressed as fractions of a second.)

Some cameras with electronically controlled shutter speeds have more choices for shutter speeds than the above list of preferred values. The more choices gives finer control over exposure.

The choice of shutter speed is not only about determining correct exposure, but also involves avoiding blur from moving objects (or from a moving camera). Shutter speeds of 1/1000 second or less are useful to photograph moving subjects, such as an airplane in flight. Photographs with the shutter open for more than 1/125 second will benefit from using a tripod to avoid inadvertent motion of a handheld camera.

2. Aperture

The aperture of the iris in the lens is usually specified by the so-called "f number", where f is the focal length of the lens divided by the diameter of the aperture.

Lenses for a SLR camera with a fixed focal length between 18 and 135 mm have a typical minimum f numbers between 1.4 and 3.5, while typical maximum f numbers are between 16 and 32.

There is a series of preferred values for f numbers marked on lenses, exposure meters, and software inside digital cameras. The preferred values are generated by successive multiplications by the the square-root of two, so that the complete series of preferred values is:
1.0, 1.4, 2.0, 2.8, 4.0, 5.6, 8, 11, 16, 22, 32

The amount of light that reaches the film or digital sensor is proportional to the square of the diameter of the lens aperture, so, for example, f=2 gives twice the illumination of f=2.8

In photographic jargon, a change in aperture of "one stop" refers to either doubling or halving the amount of light, a change of one step in the above sequence of preferred values.

The choice of aperture is not only about determining correct exposure, but also involves depth of field (i.e., the range of distances from the camera for which objects are in reasonably good focus). Smaller f numbers have less depth of field than larger f numbers. For this reason, a photographer usually focuses the lens at its maximum aperture (i.e., minimum f number) and then reduces the aperture to obtain the correct exposure. Single-lens reflex (SLR) cameras and lenses commonly remain at maximum aperture to make composition and focusing easier (i.e., brighter image in viewfinder, less depth of field), then automatically reduce the aperture to the desired value immediately before the shutter opens. Incidentally, very small apertures approximate a pinhole camera, which needs no focus.

The maximum resolution of a lens is typically obtained with an f number a few stops greater than the maximum aperture for that lens. Large f numbers (e.g., greater than 11) have resolution that is degraded by diffraction around the circumference of the iris. Small f numbers (e.g., less than 3.5) includes many light rays that are far from the central axis, which rays are often slightly distorted. Modern lenses that use aspheric elements and glass with a high index of refraction can have good resolution at small f numbers. (The f numbers in this paragraph are approximately valid for lenses designed for use on 35 mm film cameras, but are not valid for cameras that use 100 × 125 mm sheet film, or larger formats.)

3. Sensitivity

When using photographic film, the sensitivity of the film to light was related to the size of the silver halide grains in the film emulsion. In the 1950s, an American Standards Association (ASA) engineering standard explained how to determine the "ASA film speed". Later, the International Standards Organization (ISO) issued a similar standard, which was called "ISO film speed".

Fine-grain film (e.g., Kodak Panatomic-X, which had an ISO speed of 32) was inherently less sensitive to light. These low-speed films required either (a) bright light or (b) camera mounted on a tripod for long exposure times. However, these fine-grain films were capable of high resolution that could capture small details in photographs of large scenes.

For taking photographs in low-light conditions, photographers in the 1970s and 1980s commonly used Kodak Tri-X (black & white film) or Kodak Ektachrome, each of which had an ISO speed of 400.

General purpose films for amateurs commonly have ISO speeds between 100 and 200.

There is a series of preferred values for film sensitivity. The preferred values are generated by multiplying (or dividing) 100 by successive factors of 1.260 — the one-third root of two, i.e., 21/3 — and then rounding to the nearest two digits:
..., 25, 32, 40, 50, 64, 80, 100, 125, 160, 200, 250, 320, 400, ....
In practice, film manufacturers produced film with only a few film speeds.

When digital cameras became available in the late 1990s, light sensitivity was adjustable from approximately ISO 100 to at least ISO 800. As sensitivity is increased above ISO 800, digital sensors tend to become noisy, showing random bright and dark pixels. With digital sensors, there is no advantage to sensitivity below ISO 100.

4. White Balance

When using photographic color film, there were two choices: (1) daylight and (2) tungsten. So-called daylight film was designed to give proper colors when the illumination had a color temperature between 5000 and 5500 kelvin, the value of sunlight. So-called tungsten film was designed to give proper colors when the illumination has a color temperature of 3200 kelvin, the value of incandescent lamps with a tungsten filament. For any other light source, a photographer could put colored filters on the front of the lens to obtain proper color balance. More commonly, amateur photographers simply accepted the wrong colors from fluorescent lights.

Digital cameras allow the photographer to choose from a menu of different light sources. Fancy digital cameras allow one to photograph a gray or white piece of paper, and the camera automatically determines the proper white balance.

5. Contrast

Professional photographers characterize photographic film (and paper for printing negatives) by a "D vs. log(E)" graph. D on the vertical axis is either the density of the transmission or the reflectance, while E on the horizontal axis was the amount of light (i.e., exposure) required to produce that density. For negatives, the minimum density — the density of clear acetate or polyester base plus emulsion — was about 0.3, and the maximum density was about 3.

The graph has three regions: (1) an approximately horizontal region on the left where the film is grossly underexposed and the film has no response, (2) a slanting region the middle of the graph where the useful photography occurs, and (3) an approximately horizontal region on the right, where all of the silver halide grains are completely exposed.

Films for amateur photographers (e.g., Kodak Plus-X) have a moderate slope on a D log(E) graph (i.e., low contrast), so those films produce a usable image even if the photograph was under- or over-exposed by a factor of two, or even four. Films for copying printed material (photolithography) have a very steep slope on a D log(E) graph (i.e., high contrast), so that the resulting image is either black or white, with little (or no) gray. In addition to choosing the contrast of a film, one could use special developers (e.g., Kodak D-19) to increase contrast, or one could develop for longer than the recommended time to increase contrast.

There are tricks that one can play with digital image files using software like Adobe Photoshop. Adjusting contrast in Photoshop is analogous to printing a B&W negative on photographic papers with different contrast values — the original (i.e., negative or original image file) is unaffected.


A camera and lens for 35 mm film was designed to produce an image of size 36 × 24 mm. A lens with a focal length of 50 mm gave a field of view that was approximately the same as the human eye, hence lenses of this focal length were called "normal" lenses. A lens with a shorter focal length (e.g., 28 or 35 mm) was called a wide-angle lens. A lens with a longer focal length (e.g., 85, 135, or 200 mm) was called a telephoto lens.

A photographer usually selects a lens with a focal length so that the subject of the photograph fills most of the picture. However, there are occasions when a photographer may choose a long focal length lens, so that objects behind the subject (and also objects in front of the subject) are blurred, thereby emphasizing the subject. Lenses with a shorter focal length have a greater depth of field (i.e., greater range of distances for which objects are in reasonably good focus) than lenses with a longer focal length.

In the 35 mm film format, a lens with a 35 mm focal length gave the widest field of view while still displaying parallel lines as parallel in the photograph. A lens with an 18 mm focal length gives the widest field of view while still displaying straight lines as straight (as distinguished from so-called "fisheye" lenses, where straight lines are displayed as curved). Distortion caused by wideangle lenses can be removed from digital images by processing in Adobe Photoshop software.

UV filter

It is good practice to put an ultraviolet-blocking filter on the front of each camera lens. This filter has two purposes: (1) reduces haze caused by scattered ultraviolet light in sunlight in the atmosphere and (2) protects an expensive lens from scratches and dirt. An ultraviolet-blocking filter appears clear to the human eye, but actually absorbs light with a wavelength less than 390 nm. I use either a Nikon L37C or Hoya UV(0) Super Multicoated filter.

Ultraviolet-blocking filter test Sep 2007 using spectrophotometer.

Instead of an ultraviolet-blocking filter, some photographers prefer a "skylight" filter that has a pink tint, which absorbs more than 99% of the ultraviolet light and also absorbs some of the blue light, giving photographs a "warmer" tone. This is an artistic effect that has no place in scientific photography.

I have seen statements on webpages that digital cameras are not sensitive to ultraviolet light. The basic silicon photodiodes used in the sensor can be sensitive to light with wavelengths from 200 to 1100 nm, but camera manufacturers commonly install UV-absorbing and IR-absorbing filters over the sensor. Moreover, a conventional glass camera lens absorbs light with a wavelength of less than about 350 nm Because cameras are marketed to people who skipped physics (including optics!) in college, the camera manufacturers provide little technical information about their filters on the digital image sensor.

Digital sensors

Most digital image sensors are significantly smaller than the image on 35 mm film.

Most Nikon SLR digital cameras use a sensor that has dimensions 23 × 15 mm, which Nikon calls a "DX" sensor. Top of the line (i.e., expensive) Nikon SLR digital cameras use a sensor that is the same size as 35 mm film, which Nikon calls an "FX" sensor. There are two notable results from using the smaller digital sensor. First, the DX sensor requires a shorter focal length lens to produce the same field of view as the FX sensor (e.g., a 35 mm focal length lens on a DX sensor has approximately the same field of view as a 50 mm focal length lens with a FX sensor.) Second, a lens for use only with DX sensors is less expensive than a lens designed for both DX and FX sensors, because a DX-only lens needs a flat focal plane over a smaller area than an FX lens.

The sensors in some inexpensive digital cameras are smaller than the Nikon DX sensor, so that these inexpensive cameras use a lens that has a focal length as small as 1/6 of the lens with equivalent field of view for 35 mm film. Because of the short focal lengths, the cameras with tiny image sensors will have more depth-of-field than equivalent 35 mm film.

Desirable Digital Camera Features

In choosing a "point-and-shoot" digital camera with integrated lens, I think the most important feature is to choose a camera that uses AA cells instead of some proprietary battery. Inexpensive nickel metal-hydride (NiMH) AA cells (i.e., Sanyo eneloop brand) can provide 2000 mAh of capacity and retain 85% of their charge after one year of storage. In contrast, proprietary batteries that fit only a few camera models are more expensive, have less capacity, and replacements may not be available ten years after the camera is purchased. For example, in Dec 2010, the proprietary Lithium ion rechargeable battery for the Nikon D3100 camera is rated 7.4 V and 1030 mAh, and sells for $32. In contrast, six Sanyo eneloop AA cells are rated 7.2 V and 2000 mAh, and sells for $16 in Dec 2010. In this example, the AA cells have twice the energy at half the cost of a proprietary Nikon camera battery.

Because different digital cameras have different size image sensors, it is common to specify lens focal length that would give an equivalent field of view on a 35 mm film camera. In choosing a "point-and-shoot" digital camera with one integrated lens, I prefer a zoom lens that has equivalent focal lengths from 28 mm (wideangle) to at least 135 mm (telephoto). But for a SLR camera with changeable lenses, I prefer non-zoom lenses, because they tend to have higher resolution than zoom lenses.

I prefer a single-lens reflex (SLR) camera that permits manual focusing by looking into a viewfinder. Inexpensive digital cameras use an LCD display on the rear of the camera, instead of a viewfinder. It is important that the LCD display be as large as possible (3 inch diagonal is common in the year 2010) and have at least 200,000 pixels.

A manual camera for photographic film is simple and easy to operate, with adjustments only for focus, shutter speed, aperture, and film sensitivity. Each adjustment is made by turning a dedicated ring or knob, and an experienced photographer can make the adjustments while continuing to look into the viewfinder. In contrast, digital cameras tend to have adjustments selected from a menu displayed on the LCD screen on the rear of the camera. Worse, the list of features in digital cameras is cluttered with many features that should be omitted from the camera, in favor of doing processing later with software on a computer with a larger monitor than the tiny LCD screen on a digital camera.

Comparing Film to Digital

There are several important features to consider when comparing photographic film to digital image files:
  1. Spatial Resolution   Low-speed film has greater resolution than digital sensors.
  2. Dynamic Range
  3. Sensitivity   Digital sensors are more sensitive than film, which makes digital superior for low-light situations.
  4. Cost   Digital photography is less expensive than film photography, because one does not need to purchase film and pay for developing of the film.   Color film needs expensive processing at a facility operated by professionals, while digital image files can be manipulated with software on a home computer.
  5. Chemistry   There is only one opportunity to develop film, with many ways to botch the chemical processing.
  6. Storage   Unlike film, digital files will neither scratch, discolor, nor mold.
  7. Duplication   It is easy and quick to make an exact copy of a digital file.

Spatial Resolution

Kodak Panatomic-X ISO 32 black and white negative film had a resolution of approximately 170 line pairs/mm. (See Tim Vitale's article.) At two pixels per line pair (one black pixel and one white pixel), 170 line pairs/mm on a 36 × 24 mm film image has approximately 12000 × 8200 pixels. That corresponds to about 95 megapixels, giving slow black and white film higher resolution than any digital camera in Aug 2013.

The estimate in the previous paragraph ignored the oversampling required by Nyquist's Theorem. One needs to have at least 4 pixels per line pair to avoid aliasing, which requires a digital camera to have at least 380 megapixels to equal the resolution of slow black and white film. In practice, a digital camera also needs a spatial low-pass filter in front of the digital sensor to blur the image, and avoid aliasing.

Compare two state-of-the-art digital cameras with a 36 × 24 mm sensor:
  1. Leica M10 has 5952 × 3976 pixels, costs US$6950 in Aug 2013
  2. Nikon D3X has 6048 × 4032 pixels, costs US$7000 in Aug 2013
The Leica has 165 pixels/mm, the Nixon has 168 pixels/mm.

In practice, the spatial resolution of the lens often prevents one from obtaining the full resolution that is possible with film or a digital sensor. Tim Vitale says an "outstanding" lens from Nikon or Canon with a 50 mm focal length can resolve 120 line pairs/mm. A better lens from Leica or Zeiss can resolve 140 line pairs/mm.

Film with speeds slower than ISO 100 — and corresponding finer grain and higher resolution — is difficult to find in the year 2010. Kodak discontinued Panatomic black and white film (ISO 32) in the year 1989. Kodak discontinued Technical Panchromatic film (ISO 25) in the year 2003. Kodachrome ISO 25 was discontinued in the year 2002.

In the 1980s, Kodak introduced new technology (tabular-grain) that allowed film with an exposure index of ISO 400 to have fine grain and high resolution. However, further development of film technology is likely frustrated by the business consideration that film is an obsolete medium for most applications.

Dynamic Range

Slide film can record between 3.0 and 3.6 orders of magnitude (factor of 1000 to 4000) range of light intensity. Reflected light from photographic prints on paper can show a range of only about 2.0 orders of magnitude (factor of 100), in steps of about 0.01.

Digital camera manufacturers do not specify a dynamic range for their sensors and electronics, probably because few customers understand enough physics or electrical engineering to be able to interpret that specification.

There is nothing in film that is analogous to the value of the least-significant bit in digital data. The closest thing is that the human eye can barely perceive a difference of 0.01 in reflectance from a reflected image on paper. A step of 0.01 in density or reflectance is equivalent to 1/30 of an f-stop, i.e.,
21/30 = 100.01
Given that prints on paper have a range of reflectance of about 2.0 orders of magnitude, a minimum perceptible difference in density of 0.01 corresponds to a digital range of about 200 steps spaced logarithmically.

The human eye and photographic film both have a response that is proportional to the logarithm of the luminous intensity. In contrast, silicon photodiodes have a current (or charge) that is a linear function of exposure. The analog-to-digital converter in a digital camera is also a linear device. Inexpensive digital cameras have an 8-bit A-to-D converter (0 to 255 range), while better digital cameras record at least 12 bits of intensity data per color (range from 0 to 4095).

Digital cameras commonly produce an JPEG file with 8-bits of intensity for each of three colors. Such a JPEG file has a typical dynamic range of 211, or about 103.3. The JPEG file is created by converting linear intensity data from the A-to-D converter to a logarithmic scale.


In the 1980s, photographic film commonly used by photographers had speeds between ISO 25 and ISO 400. Faster film had large silver halide grains, and their prints looked like they were printed on sandpaper.

Digital image sensors commonly have effective speeds at least as high as ISO 1600. The minimum speed of digital cameras is commonly ISO 100, because there is no advantage to using less sensitivity.


Once one owns a digital camera and memory card, there is nothing else to purchase.

For film photography, one must purchase each roll of film and also pay for developing of the film, which is a significant and continuing cost of chemical photography.

A single-lens reflex camera body with a digital sensor is more expensive than a similar body for photographic film. In August 2005, when I wrote the first draft of this webpage, discount camera stores were selling a Nikon FM3 manual camera body for film for $600, and a Nikon D70 digital camera body (6 megapixels and 1 gigabyte memory card) for $850.   However, one must also consider the cost of film and developing. In August 2005, one 36 exposure roll of Kodachrome 64 cost about $ 6, and Kodalux processing of this film cost about $ 9, making each slide cost approximately $ 0.40.   With this example from August 2005, the digital camera will be cheaper after exposing and processing only 17 rolls of 36-exposure color film.

Furthermore, when using photographic film, a careful photographer will take two or three photographs of the same scene, each with slightly different exposures. After the slides are returned from the processing laboratory, the photographer will likely discard at least half of the slides. Because one can see and print digital photographs immediately after the photograph was taken, one can be certain that the exposure and focus are correct when the photographs are being taken, and immediately discard improperly exposed photographs.


With film photography, there is only one opportunity to develop the film. If the chemical solutions are weak, wrong temperature, wrong developing time, etc. then the images can be ruined or significantly degraded. If there is a light leak during prior to finishing chemical processing, the images will almost certainly be ruined. People commonly mail color film to a distant laboratory for processing, and the film is sometimes lost in transit or mislabeled at the laboratory, so the photographer never receives the processed film. As mentioned in the previous section, chemical processing also increases the cost of film photography.

All of these problems are neatly solved with digital photography.


I store my slides in metal boxes that each hold 300 slides. Images on photographic film can be damaged by mold. Colors in processed photographic film can change with time, especially when the images are illuminated by bright light or stored at high temperatures.

Digital files are stable with time, so will not degrade. Digital files require less volume for storage, compared to prints or slides. I write HTML files to index my digital photographs on my computer, so I can use a webbrowser to display both my index and the images, eliminating the need for prints in a photo album.

Librarians and archivists are concerned that a JPG file format on a floppy disk or CD-R may not be readable one hundred years in the future, while a print will still be visible. Note that it is the medium (e.g., floppy disk or CD-R) that has a limited lifetime or lack of mechanical reader in the future. Prints also have a finite lifetime: prints will fade with time, especially if they were inadequately washed after development and fixation.


When duplicating a photographic slide or negative, the copy always has more grain than the original. Furthermore, the colors will not duplicate precisely, because the duplicating film is not the same as the original color film. In contrast, an exact copy can be easily made of digital files.

One can duplicate prints by using a flatbed scanner to convert the print to a digital file. However, affordable scanners for negatives or slides have fewer pixels than modern digital cameras, and therefore the scanners lack resolution to copy all of the detail in the original negative or slide.


Unless you will be making very large prints (e.g., mural for a wall of a building), digital is better than film. Modern digital cameras have adequate spatial resolution, digital is cheaper than film, digital images can be exactly duplicated, and digital cameras have finer control over color balance than film.


Note that my disclaimer applies to this entire webpage, including the links to other websites. I am not making any endorsements or recommendations here. This list of links is in alphabetical order.

Camera & Lenses

Canon-USA homepage has separate webpages for consumer and professional cameras

Leica cameras in Germany, Leica USA   Leica makes only rangefinder cameras, not single-lens reflex (SLR).

Nikon-USA   official Nikon history


Pentax, now a subsidiary of Ricoh

Sony homepage   Sony makes both compact cameras and digital SLR cameras.

Zeiss lenses for cameras made by Nikon (ZF.2), Canon (ZE), or Pentax (ZK).

Any of these brands of cameras/lenses can produce good photographs. I personally use Nikon, because in 1973 I was impressed with the Nikon bayonet lens mount (Pentax then had screw threads on its lenses) and the large variety of Nikon lenses. After I acquired a collection of Nikon lenses during 1973-1990, I naturally continued to use Nikon camera bodies.

Most modern digital camera bodies are designed for autofocusing lenses. If you want to use old manual focus lenses, you need to replace the standard matte focusing screen with a screen similar to the K3 screen in the Nikon FM3 camera body, which has a microprism ring with a split-image inside the ring. One source for this screen is KatzEye in Greenfield, Massachusetts.

Nikon has included a computer chip in their Nikkor lenses designed since the 1990s. The chip transmits the focal length and aperture to the camera, for use in metering on modern camera bodies. Legacy2Digital in Oregon can retrofit an old Nikkor manual-focus lens with a fixed focal length (type AI or AI-S) to include a chip to make the lens equivalent to a type AI-P lens. The conversion to AI-P may be desirable if either Note that old manual-focus zoom lenses can not be modified with a chip that shows the actual focal length of the lens. I have not personally had any of my old lenses retrofitted with a CPU-chip.

All Nikkor lenses designed since 1992 are type D lenses, the chip also transmits the distance of the focused subject to the camera, for use in automatically setting a flash unit. Modern Nikon digital camera bodies include the focal length, aperture, and distance data (when available from the lens) in the EXIF part of the JPEG file output by the camera.


three major manufacturers
FujiFilm homepage (no B&W film)
Velvia 50 color slide film
Ilford B&W film (ISO 50-3200) and paper
Kodak homepage
amateur color print film (no amateur B&W or color slide film in Oct 2010)
professional black & white film
professional color negative film
professional color slide film

other people's websites

Note that people have strong opinions about what is the best film, best camera, best lens, etc.

Charles Doswell, Ph.D. in meteorology, his tips for photographing lightning.

Philip Greenspun, Ph.D. in computer science, film recommendations in 1996.

Thom Hogan has detailed webpages on Nikon equipment.

Rick Housh's list of Nikon lens hoods, compiled in 2002-2003.

Norman Koren is a physicist who has used digital cameras since April 2003. He now writes image test software for digital cameras and lenses. His website contains numerous tutorials on photography.

Jeremy McCreary digital photography, including infrared

Fredrik Rasmussen reviews Nikon equipment.

Ken Rockwell, BSEE degree, reviews Nikon, Leica, and Canon equipment, earns living partly from links at his website.

Bjørn Rørslett, Ph.D. in ecology, nature photographer, evaluates Nikon lenses, has webpages on infrared and ultraviolet light photography. In 2012, his website merged with a website operated by Dallas Dahms, a professional photographer in South Africa.

Steve Sanders and others review digital cameras.

Photography in Malaysia, has technical information on discontinued products from Nikon, Canon, Olympus, Leica.

Roland Vink has very useful webpages on Nikkor lenses, including a table of old Nikkor lenses with serial numbers that is useful for evaluating used lenses.   He also has a table of lens hoods, cases, and other accessories for each lens.

Tim Vitale does conservation work with film.

This document is at
created August 2005, modified 4 Oct 2013

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