Digital Photography vs Traditional Photography exposure & film speed?
	Hopefully we are now well versed in resolution, image size, ccd array density, and how light is converted to an image. So now we must look at the way a digital camera works verses the traditional camera. There are similarities and some important differences. Digital Camera Parts ccd 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. So here is the $64,000 question. 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. The good features include the ability to balance any type of light source to white (or neutral tone). Very useful when the light is tinted. The bad news is that the camera will tend to remember this balance point even when you move it to another light source. You must remember to reset it before use in each new environment. 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. 1.) Little or no aperture control and thus little or no depth of field. the vast majority of digital cameras have no physical way to change their aperture. It is usually tied directly to their exposure system and cannot be controlled beyond zoom level. The creative process of controlling focus with depth of field is severely limited within the camera, but can be achieved in post image work-up. (i.e. - using Photoshop.) 2.) Limited shutter speed selection, especially at the higher (faster) speeds. Zoom lenses tend to have higher aperture values so they require longer not shorter exposure times. Most of he digital cameras are well armed to take long duration pictures, but most use their flash synchronisation speed as their high speed. This can make it difficult to use high speed for sports or action shots. 3.) A zoom lens is standard in most models and typically runs from 2:1 to 3:1. The zoom lenses built in to most of the digital cameras provide a nice range of magnification and are really very good. Since the under $1000 cameras have yet to be equipped with removal lenses, the zooms are a nice compromise. Some cameras also offer "digital zoom", and this is virtually useless for picture taking. Digital zooms simply use pixel doubling to make the image appear larger. the result is a bigger and fuzzier image. There may be a use for digital zooming with reguard to meter reading or focusing in some cases. 4.) 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. Digital cameras are small and hence the flash tends to be in-line with the lens. This provides excellent redeye in most people pictures and extreme silver or gold eye in most animals. Many models now incorporate redeye compensation by using a pre flash, and this works in some cases, but with animals it seems to provide them with the timing necessary to just move their eyes into perfect alignment with the flash for excellent glowing eye shots. 5.) 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. The cameras that do provide good "macro" capability seem to be very precise and excellent results can be achieved. The one problem with most of these cameras is their inability to override auto-focus. In closeup situations, with extremely limited depth of field, focus is critical, and it is often necessary to trick the camera or find strange work-arounds to maintain the focus on your selected spot. 6.) Cameras are electronic and hence use batteries. Be certain that the model you buy uses standard batteries as you will use them at an unbelievable rate. These cameras tend to use up batteries faster than almost any appliance I have ever seen. When possible use nickel-metal-hydride rechargeable batteries as they are inexpensive and last longer than most. The ability to turn off the external LCD digital display is very desirable as these displays causes rapid battery turn over. 7.) Digital Cameras use some type of memory to store images. Be certain the model you buy uses some kind of standard removable memory module. Memory modules provide a means to capture more images without the need to download them to computer. Be certain the model you select uses a standard memory module and not some proprietary module that can only be purchased form one source. The standard modules tend to be less expensive and their development is accelerated by a wider audience. 8.) Recovery time between exposures can be long. Some cameras take many seconds to recover before they can shoot another image. There is a time necessary for the ccd cell to drop back below a certain threshold after it has been exposed to light. The time varies from camera to camera. The only way to really know this value is to try the camera and see how long it takes. Some cameras take up to 20-30 seconds to recover. If you are shooting fast action situations, then these cameras should be avoided. So what are the Advantages of Digital Cameras In a word "TIME". Digital photography offers almost instantaneous feed back. You can shot the picture and see the result in a matter of minutes if not seconds. There is no "processing" step and no one or two day turnaround. You will know within a matter of minutes whether you have the shot you need, and you will not worry about taking multiple shots to get the "right one". Once the camera is purchased you can reuse the memory over and over, so throw away shots cost no more than keepers. Some people might argue that this promotes poor shot selection or sloppiness. I admit I tend to take less time in set up than I did in the traditional world, I know I can reshot most of my pictures if I fail to get what I want on the first try, but this also gives me latitude to try things I probably would not have done with traditional film. The feed back from the computer and the darkroom functions built in to programs like Photoshop are real spoilers. I used to do my own color dark room work, and would often work many hours to produce a single usable print. There were many techniques I simply would never try as they were far to time consuming and chancy, like picture within picture. With my digital dark room I am ready to tackle almost anything I can imagine. 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. The ccd cells tend to be smaller in size than 35 mm film. Virtually all 35 mm lenses act like telephoto lenses when used in conjunction with a ccd cell. Digital camera lenses tend to be very small in focal length compared to their 35 mm brothers. Different digital cameras use differently sized ccd cells, so there is no single one to one correspondence with focal length equivalents. A typical zoom range is from 7 or 9 mm to 20 or 30 mm, and these correspond to roughly a 28 mm to 140 mm zoom in the 35 mm world. For this reason a standard 50 mm lens on a 35 mm camera would be a medium telephoto if used to focus on a digital ccd cell. A nice 9 mm fisheye lens in the 35 mm world would be just a little bit on the wide angle side of a normal lens for a digital camera. Fuji and other companies are working on producing physically larger ccd cells so standard 35 mm camera bodies may eventually be used for digital photography, and become more affordable.