Module 21 

Home

Catalog

Contact Us

Post-test

Module 21:

Basics of Photography,

Part 1

The material is best view at a screen resolution of at least 1024 by 768.  You can easily check or change your screen resolution yourself.  For windows, go to the desktop and move your mouse to a blank part of the screen. Right click the mouse and click on "properties".  Click on the settings tab.  Use the slider to change the screen resolution if needed, and click "OK".

Introduction

The Eye-Camera Analogy

Film

Exposure

Film Speed

Resolution, Grain, and Pixels

Film Speed vs. Resolution

Film vs. Digital

Black & White vs. Color

Negative, Slides, and Digital Images

Contrast

Panchromatic vs. Orthochromatic

35mm vs. Other Formats

White Balance

Introduction

Everyone likes to look at photographs, and most

people like to take photographs.  There is something fascinating about the ability to freeze time, to encapsulate a moment in a picture, to produce a seemingly exact reproduction of a visual image.

All of us, even the experienced, would like to improve our ability to produce quality photos.  Photography is governed by some complex physical principles of optics, chemistry, and electronics.  Fortunately, we don't have to understand the complexities in order to produce good photographs, but we do have to obey some rules and relationships that those complexities dictate.

The Eye-Camera Analogy

There is a useful parallel between the function of the human eye and the function of a camera:

• The retina of the eye is like the film in the camera.  This is the light sensitive part that captures the image.

• The cornea and lens of the eye are similar to a compound lens system in a camera.  This is the part that focuses the light on the film or the retina.

• The iris of the eye is like a variable aperture in a camera.  This is a part that regulates the amount of light that reaches the film or the retina.

The camera analogy is particularly useful when explaining to Mrs. Jones, who has macular degeneration, why cataract surgery may not make her vision much better.  Unfortunately, the anatomy and physiology of the eye does not make photography much easier to understand.  This is because the eye is infinitely more complex, adjustable, and responsive than the most sophisticated camera.

The Film

Exposure

To better understand photography, let's start with the business end of the camera; the film.  The normal human retina easily adjusts to a wide range of light intensity and color and contrast variations.  Film, on the other hand, has to be exposed with just the right amount of light to produce a good image.  This is called exposure latitude, and the exposure latitude of the best film is very narrow compared to the human eye.

Film Speed

Film is manufactured with different light sensitivities.  Most digital sensors also have variable sensitivity.  You might think that it would be desirable to use the most sensitive film available.  The problem is that there is a trade-off between light sensitivity and image quality.  As sensitivity increases, image quality generally decreases.  Therefore, you want to use a film, or a digital sensitivity setting, that has just enough sensitivity for the lighting conditions.

Film and digital light sensitivity are rated according to an international standard.  This is the ISO (International Standards Organization) rating, or "speed" of the film or digital sensor.  The "slowest" film, rated ISO 25, requires much more light to be proper exposed than a "fast" film, perhaps rated ISO 400.  ISO numbers typically range from 25 to 6400.  The most common films range from ISO 100 to ISO 1600. 

There is an important mathematical relationship between ISO numbers.  A film with an ISO of 200 requires half as much light for proper exposure as an ISO 100 film does.  A film with ISO 200 requires twice as much light for proper exposure as an ISO 400 film, and four times as much light as an ISO 800 film.

In other words, the lower the ISO number, the slower the film is and the more light that is needed for proper exposure.  Doubling the ISO number cuts the amount of light required by half, and vice-versa.

Remember that slower films generally have better image quality in terms of color saturation and rendition, and resolving power (detail).  Faster films are sometimes needed in low light situations, or when you want to manipulate the shutter speed or aperture in a way that will cut down the amount of light getting to the film (more on this latter).

The light meter in the camera needs to "know" what film speed is being used so that settings can be adjusted for proper exposure.  On some cameras this requires setting a film speed dial to the correct number.  Many automatic cameras have sensors that "read" the ISO number from a code marked on the film canister.

Resolution, Grain, and Pixels

Color and black & white film is composed of tiny light sensitive particles called grain.  The smaller the grain particles are, the better the resolving power of the film.  A high resolution film is able to record more detail than a lower resolution film.  Remember that the slower the film is, the smaller the grain pattern and the greater the resolution.  You can see the grain pattern in any film by enlarging the image to the point where it becomes obvious.  If you want to make significant enlargement of your photograph, you will want to use a slower, high resolution film with a small grain pattern.

Digital sensors (CCDs) are composed of small light sensitive cells called pixels.  The more pixels there are per inch of sensor, the greater the resolving power of the sensor.  If the sensor has 2000 pixels in a row and 1200 rows of pixels, then you can multiply 2000 x 1200 to get a 2,400,000 (2.4 megapixel) sensor.  

More megapixels means larger file sizes and more storage space.  Digital cameras use small electronic "cards" to store the picture files.  The larger the file size is, the fewer pictures that can be stored on a given card.  A photo taken with a 5 megapixel camera and stored as a .tiff file can be up to 17 megabytes in size.  A "byte" is the smallest piece of digital information.  A megabyte is a million bytes.  In 1995, many computers had a total hard drive capacity of 20 megabytes.  But don't despair, an 8x10 print of excellent quality can be produced from a 2 megabyte .jpg image file recorded with a 3 megapixel camera.

Some file types "compress" the digital information in the file to make the file size smaller.  The problem with compression is that some of the picture "information" is lost in the process, thus decreasing the resolution of the image.  

A "tiff" file, with the file extension .tiff, is a "loss-less" file type that is not compressed and retains all the image information.  A "jay-peg" file, with the file extension .jpg is a file with variable compression.  This is a popular picture file type that is a good compromise between file size and picture quality.  Smaller file sizes take less time to send or download over the internet, and they take up less space in the storage system.

When using film, remember the general rule that you want to use the slowest film that will work for the given lighting situation, taking into account special camera setting requirements.  Examples:

ISO 100 film is used for fundus photography for the same reasons.  The electronic flash of the retina camera provides plenty of light.

ISO 400 film is commonly used for fluorescein angiography to provide a better image under the reduced illumination caused by the filters.

Film vs. Digital

Compared to film, the two greatest advantages of digital images are cost and convenience.  

Picture files can be downloaded from the camera storage media to a computer or another storage device such as a CD.  The camera media card can then be erased and used over again and again.  The biggest recurring cost for the digital camera is batteries to drive the electronics and the flash, and this cost can be minimized by using rechargeable batteries.  However, some cost savings can evaporate if images are routinely printed using a photo quality printer, which generally has high paper and ink costs.  You must also take into account that a computer is needed and that a good digital camera may cost more than a good film camera.

Digital images can be sent over the internet, stored and transported inexpensively, and can be cataloged and sorted using special software.  

Black & White vs. Color

The most well known B&W photographer was Ansel Adams.  He was a master of the large format camera, and he developed a "zone system" that optimized the developing and printing process to produce stunning photographs.  For more information, search "ansel adams" on the web.

Some specialized digital cameras, such as used for fluorescein angiography, are designed for B&W photography, but most digital cameras will not take a B&W photograph.  A B&W photo can be rendered after the fact from a color digital image by using editing software.  The process is one that converts the image to "greyscale".  Below is a color digital photo, and the same photo converted to greyscale.

Digital cameras produce positive images, meaning when viewed in the original state, the image appears the same as it does to the eye.  Film, however, can be either a positive film, or a negative film. 

When developed, a negative film renders an image that is opposite in tone from what we see with the eye.  The negative must be printed in order to reverse the image.  The blacks on a B&W negative print as areas of white on the print and vice versa.  Although there are specialized B&W positive sheet films, 35mm B&W film can be considered to be almost exclusively negative film.  The color film that we buy for our snapshots is almost exclusively negative film.  Any film that has "color" at the end of the name, such as Kodacolor or Fujicolor, is a negative film.

When developed, a positive film renders an image that appears the same in tone as what we see with the eye.  This is commonly called "slide" film.  Although slide film can be printed, it is usually viewed by projection or by retro-illumination in a slide viewer or on a light table.  Any film that has "chrome" at the end of the name, such as Kodachrome or Fujichrome, is a slide film.

A color negative image on the right.

A B&W negative image on the right.

A nice characteristic of a digital image is that copy after copy can be made from the original without losing any of the original information.  Of course,  a troublesome characteristic of a digital image is that the image can be altered artificially.  There are standards being developed in the scientific and medical communities to try to insure that original digital photographic information is preserved and identified as such.

Contrast has to do with the number (range) of shades of gray that the film will record between white and black. A high contrast film will record fewer shades of gray. Some films have a higher contrast index than others.

Contrast can be changed by the development process. Faster films usually have a higher contrast index. Generally, the higher the contrast is, the less detail that is recorded on film.

The contrast on digital images can be adjusted to achieve an optimum level.  Many digital cameras have a contrast adjustment function, or the contrast can be adjusted with photo editing software.

When making a positive print from a black and white negative, image detail may be lost and the contrast may be altered.  For this reason, some retina specialists prefer to read the negative image of a fluoresein angiogram instead of a print made from the negative.

Panchromatic films are sensitive to all wavelengths of light. B&W film and color slide film are panchromatic and must be handled in total darkness in the darkroom until they are developed.

Orthochromatic films are sensitive only to blue and green light. Transparency B&W films (used to print fluorescein angiogram positives) and B&W papers are "ortho" and can be handled in the light of a darkroom safelight because they are not sensitive to the red end of the spectrum.

When making an enlarged print from a negative, or part of a negative, you want to start with a large negative.  The larger the negative is, the more resolution (detail) there can potentially be in the print.

The ideal situation would be to make an 8 x 10 print from an 8 x 10 negative.  Although there are cameras that handle 8 x 10 negatives, they are so large as to make them impractical for most situations.  Ansel Adams worked with 5 x 7 inch negatives.

35 mm film has become the standard film format.  This frame is a rectangle measuring 35 x 24 mm.  This size is a good compromise between quality and convenience.  A good quality 8 x 10 print can be made from a 35 mm negative, and 35 mm cameras can be small enough to be conveniently carried anywhere.

There are formats that are smaller than 35 mm, but the prints from the miniature cameras that use this film cannot be printed larger than about 4 x 6 inches without suffering in image quality.

For practical purposes, a 3 megapixel sensor in a digital camera has roughly the same resolving power as 35 mm film.

The center image is the relative size of an 8 x 10 inch print, compared to the size of  a 35 mm negative on the left, and a 5 x 7 inch negative on the right.

When we "see" an object, our visual system is sensing the light reflected from the object.  A red rose in bright daylight looks "red" because the plant matter has absorbed all of the visible wavelengths of the daylight except the red wavelength, which is reflected by the plant matter.  The shade of red that we perceive is affected by the quality of the light that is directed toward, and reflected from, the object.  

Not all "white" light is the same, the quality of the light depends upon the source.  White light comes in different "temperatures".  Unfiltered sunlight is the standard white light.  Compared to direct sunlight, sunlight filtered through clouds is "cooler", meaning colors shift more toward the green and blue end of the spectrum.  Light from fluorescent light bulbs is also cool.  Compared to direct sunlight, light from an incandescent light bulb is "warm", meaning colors shift more toward the orange and red end of the spectrum.

At one time, color film came in two basic temperatures, "daylight" and "tungsten".  Daylight film was used in outdoor photography and with electronic flash.  Tungsten film was used for photography in artificial light such as incandescent illumination.  It's hard to find tungsten film now, the vast majority of snapshots are taken in either daylight or with electronic flash, which has the same color temperature as daylight.

The digital camera has a white balance setting that can be changed, depending upon the light source.  The default setting is daylight.  Many digital cameras have settings for a cloudy day, tungsten illumination, fluorescent illumination, and an automatic setting that is supposed to detect the type of white balance adjustment needed.

In the digital photo below-left, the candle was illuminated with a tungsten (regular light bulb) light source, but the white balance was set for daylight.  After adjusting the white balance for tungsten lighting, the photo of the white candle is more true-to-life (below-right).