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To most photographers Digital cameras look, feel, and shoot almost like film cameras. Both have a view finder, lens, light sensors, flash, and shutter release button. They both use common terms like ISO (International Standards Organization) sensitivity, shutter speeds, F/stop, focal length, etc. This is a misleading simplification.

Cameras

For the purpose of this discussion I am confining my observations to consumer digital cameras that mere mortals can afford. (Less than $500.00) There are many high end cameras priced 2 to 5 times that amount.

While it is relatively easy to compare digital cameras to each other by their numbers, Film cameras can be compared by their relative merits. There is no easy way to do head-to-head, point-by-point comparisons between these two technologies. The most obvious difference between the two is that digital cameras record the images electronically while conventional film cameras record the images on light sensitive film. But it doesn’t end here.

The overall size and weight of my digital camera is much less than my 35mm film camera. The image sensor on my digital camera is about 1/4 the area of the 1" x1 1/2" 35mm film frame. The smaller image size reduces the 10x zoom lens size to roughly 1/4 the size of a similar lens on the film camera; while it is effectively equivalent to an optical 38mm to 380mm zoom lens, its real focal length is about 9mm to 90mm. This lens covers a zoom range from a moderate wide angle to a substantial telephoto. There is an additional 3x digital zoom that feature extends the maximum zoom range
to an equivalent 1140mm. Using the digital zoom utilizes a smaller (cropped) portion of the image sensor which lowers the overall pixel resolution of the image. Since you can crop the image later using any photo editing program (with a commensurate loss of pixel resolution), I tend to ignore the in-camera digital zoom feature. I purchased two 256Mb memory chips with the camera and can record 195 maximum resolution
exposures on each chip before needing to download the photos to my computer’s hard drive or to a CD (or both). I’m then able to recycle the chips for re use. The battery in the camera lasted for more than two days of shooting before needing recharging.

Most digital cameras do not have an ISO setting or a diaphragm controlling the lens opening. The ISO film speed rating and F/stop equivalents are controlled by the gain applied to the sensor. Only a few digital cameras have a shutter that is only used to protect the sensor from being blinded by bright light. In place of a conventional shutter,
the sensor is switched on and off electronically at speeds unobtainable on most conventional cameras. The rapid switching of the electronic shutter, however, is free of the limitations of mechanical shutters. This permits many digital still cameras to take short video clips, limited only by the memory capacity of the image storage chip.

Images captured by the image chip are electronically processed and transferred to a removable storage chip. This clearing of the image chip and transferring of the image to the memory chip usually takes a fraction of a second, which can limit the rate of taking sequential pictures.

Photo (film purists) say that digital imagery can never surpass or even equal the tonality, resolution or color fidelity of silver halide crystals. While the Digital converts swear that pixel based images can capture more detail, greater dynamic range, and more accurate color. The answer is more subjective and more complex than just comparing the sheer size of film granularity to the digital pixel count and the color accuracy measurements of the two technologies. Let’s take a closer look at the
arguments of each side.

Film

Images on film are captured when light causes molecular changes in tiny silver halide crystals on the film, which are later developed and stabilized into visible images in a series of chemical baths. The smaller the crystals the greater the detail that can be recorded. However, there is a tradeoff here. Larger crystals are more photo reactive to light. Which leads to the great variety of film choices with different ISO sensitivity ratings, from a low speed rating of 20 through high speeds of 1600 and more. The finer the grain (Crystal) size, the lower sensitivity to light, but the more detail and tonality the film can record. The larger grain films record images at much lower light levels and records much less detail, with less tonality. Furthermore when the images are enlarged the larger granules can become obvious to the eye. Color film has three layers of silver halide grains sensitized to record different colors (red, green. and blue), which when combined create the full color image. The color balance (white balance) of the film is set for daylight or tungsten light when the film is manufactured. A single 35mm frame can contain an estimated 15 million silver halide grains. Film is analog, not digital, so
each crystal is, within limits, infinitely variable. This allows film to record continuous tone images. The grains are more tightly packed than the highest density of pixels that can be placed on a digital image sensor.

Film has had 160+ years of development and improvements have brought us to the current state of film imagery as we know it today.

Digital Images

The birth of digital imagery doesn’t have an exact date—the mid to late ’60s is close enough—followed by a remarkable whirlwind of development and growth in a short time. Digital image capture is still almost in its infancy, having been around in labs and studios for a couple of decades, and becoming a practical consumer device in only the past 8-9 years. There remains considerable room for performance, interface, and image quality improvement, and these are prime targets for new technological
breakthroughs. That said, the present state of development produces a remarkable level of image quality.

The image sensor is a silicon semiconductor that captures photons (light) and converts them to electrons is at the heart of all digital cameras. The electrons are once again converted to voltages which are measured and turned into digital data. All this is done in a microsecond and at a microscopic level. The CCD (Charge Coupled Device) is the standard against which all new sensors are compared. Image sensors continue to be redesigned and reinvented by Sony, Philips, Kodak, Matsushita, Fuji, and Sharp. Newer CMOS (Complementary Metal Oxide Semiconductor) sensor chips are moving into the mainstream of digital cameras. Both CMOS and CCDs were invented as solid-state memory storage devices.

A Side Note

Like most digital development, the need for image sensors came from government intelligence and space programs in the ’60s. Air Force and CIA satellites needed to be calibrated for scale. Shapes large enough to be seen from space were secretly mown into Western corn fields. (Yes! the mysterious crop circles were signs from space, but entirely human in nature.)

Sensor Chip

In a most simplified form I’ll try to describe the sensor chip. Unlike the silver halide grains in film which are distributed on a flat plane and react to light striking the film from any angle, the pixels on a digital sensor require the light to strike the sensor at near perpendicular angles. To compensate, each pixel is covered by a micro lens to re-direct the light coming from the camera lens which is also optimized to meet the
sensor requirements. Each pixel is also covered by a color filter (Red, Green, or Blue) to record the data necessary for the reconstruction of a color image. The pixels are arranged in rows with twice as many green filtered cells than the red and blue in order to match the sensitivity of the eye which is more sensitive to green light.

The pixels are arranged in a Bayer Pattern as follows

RGRGRGRGRG
GBGBGBGBGB
RGRGRGRGRG
GBGBGBGBGB

The data is transferred row by row, ultimately to the memory chip where the image is reconstructed.

The scale of detail of a digital camera is measured in the total number of lines it can resolve before they begin to run together. A typical CCD can resolve 2000-3000 lines/inch. Fine grain color film can resolve 2200 lines/mm that’s more than 50 times better than the raw resolution of Digital. In real life, despite the difference, the respective technologies are much closer than the numbers indicate. That is because of differences in the range of data capable of being reproduced by the various output
devices: film, printers, and monitors. Although film has much higher resolution than digital, they both come up against an inexorable bottleneck: the output device. For film that’s the number of lines photographic paper is capable of resolving; for pixels its the number of lines that can be resolved by ink jet printers or monitors. Both paper
technologies are similar. The net result is that with all the extra resolution film captures, it will produce about the same amount of detail in print as is captured by an image sensor.

Regarding tonality, there is a tossup. While the analog film can by its nature produce greater tonality, digital technology can capture much higher dynamic range. Average film can record a dynamic range of about 4; that translates to about 6 or 7 f/stops (anything above or below that records as monochromatic black or white). Digital can capture 11 or more f/stops of data, roughly twice that of film. The extra dynamic range is useful only if the output device can accurately reproduce it.

There are other technical differences that translate into digital or film superiority, such as color fidelity, saturation, white balance etc. At day’s end, a good photographer can get equal quality from either technology. It is entirely possible to use a digital camera and the new multicolor ink jet printers to produce images that can rival Ansel Adams-like museum quality prints...

I have taken more than 2000 pictures with my new toy in Hong Kong and Thaiiland, and this spring while trekking along the Louis and Clark trail. The money saved in film, processing, and printing more than paid for the camera. The instant review and the ability to transmit photos are other reasons to go digital. When in Southeast Asia, I was never beyond the range of an Internet cafe, or in the Mid West a Wallgreens Drug Store, where I could get prints instantly from the camera chip or from a CD.

Stay tuned—the technology changes almost daily.

Before I sign off, I would like to credit, the following for the mass of information found on the web I especially thank Dave’s many digital camera reviews found at www.imaging-resource.com , and the many articles by Sally Weiner Grotta and Daniel Grotta on www.cnet.com, and www.extremetech.com.

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