Digital Photography Fundamentals

Rule One - all digital cameras capture information at 72 dots per inch (DPI) regardless of their total pixel count and overall resolution. 72 DPI defines digital photography and yes it is both with still video cameras and digital camcorders. ( Just as a point of information, digital camcorders use 720 x 480 pixels as their standard resolution, but still present data at 72 DPI. )

The 72 DPI was chosen because digital play back happened originally on Television sets, and guess what. TV sets play back at 72 DPI. Computer monitors for the most part also playback at or about 72 DPI. For the purposes of the remainder of this article I will treat 72 DPI and 75 DPI as totally equivalent. This is because I hate left overs when doing math. Just remember for the remainder of this document 72 DPI = 75 DPI.

Rule of Thumb: Enlarge with hardware, reduce with software.

No. of Pixels versus Web and Printed Size

A 1 or 2 mega pixel camera is totally sufficient for virtually all WEB use. Images taken from those cameras are reduced in size before use, so you end up throwing away a large part of the original information in most cases. For print use, you may wish to consider the higher resolution cameras or even slide scanners.

Digital Camera Partsccd cell - replaces the film and is used to create the image.shutter - used to control the amount of light that hits the cell.Iris - not always present on a digital camera, and often not controllable, but provides the same functional control of light intensity as the traditional one does.lens - used to focus the image on the ccd cell.The digital camera is similar in design to a traditional camera, but the actually operation is often very different. In place of the film there is a ccd cell which converts light energy to a voltage. An A/D converter then converts the voltage to a number which is stored in memory.

What is the ISO value of the ccd cell (film speed), and what is its light balance, daylight or tungsten?

The answer to these two questions provides insight into the workings of a digital camera. A ccd cell can change its sensitivity to light depending on the bias voltage of the cell. It has a "variable" ISO rating and can be changed as needed within a specified range. Since the ccd cell has a fixed set of colored filters which collect the different wavelengths of light, the ccd is not balanced to any particular light type. Electronic controls on many digital cameras provide for "white balance".

White balance is a way to position the ccd in the color spectrum precisely where you want it. Fundamentally you place a white object (card) in front of the lens, and tell the camera that based on the current light it should consider this card to be pure white. It will adjust everything else accordingly. There are good and bad features to this methodology.

Many of today's digital cameras have selections for daylight, flash, and tungsten, as well as the ability to set the "white balance" manually. These seem to work pretty well, and together with the manual mode digital cameras are really good at correct light balance.

The sensitivity of the ccd can be changed via electronics, so many of the cameras do not rely on a fixed ISO value for their metering. Here is a prime difference between the digital camera and the traditional camera. The "film speed" (ISO value) is not fixed in a ccd camera and can be adjusted on the fly. It has limited range, but with today's models, it is fairly wide.

In the traditional (film) camera the film speed is fixed and only the shutter speed and aperture can be used to control exposure. In the digital camera, film speed, shutter speed, and aperture can be varied. Not all digital cameras have manual aperture controls, and in the case of these cameras, the shutter speed and film speed are used to balance the exposure with a fixed aperture. These cameras offer little or no depth of field. The f-stop is actually set by the zoom level of these cameras.

Digital cameras lack the same degree of standardization as their 35 mm counter parts. It is necessary to look carefully at the documentation and technical specifications to determine how any particular camera may operate. Here are few generalities that are common to the vast majority of less expensive cameras.

Little or no aperture control and thus little or no depth of field.

Limited shutter speed selection, especially at the higher (faster) speeds.

A zoom lens is standard in most models and typically runs from 2:1 to 3:1.

Flash is built in and automatic in most models, that's the good news. The bad news is that flash is built in and automatic in most models.

Limited closeup ability. Although several of the cameras offer a "macro" mode, most are limited to about 8" to 10" for closeup work. It is necessary to look carefully at the documentation to determine their nearest focal point.

Cameras are electronic and hence use batteries.

Digital Cameras use some type of memory to store images. Be certain the model you buy uses some kind of standard removable memory module.

Recovery time between exposures can be long.

Digital Cameras give instant feedback. You can reuse memory instantly. My camera uses a 32 MB Flash Card.

It is necessary to understand the limits imposed by digital photography and you must be willing to accept them. Resolution is not as good as the traditional film method, but the gap is closing rapidly. Color saturation is nearly as good, but low light sensitivity and the ability to pull out shadow detail is still behind.

Standard camera controls are coming, but are not here yet in most consumer models. There are digital cameras that make use of more traditional 35 mm style bodies, but these tend to run between $3000 and $5000. It would be nice if you could just take a digital camera back and place it in the film plane of your standard 35 mm camera, but unfortunately there is a problem.

                                     

Light Box and Flash