Part 19 - Digital Imaging Formats

Much of the current photography jargon has its roots in traditional film-based photography. The purpose of this article is to provide the beginning digital photographer with an understanding of the terms being used today to describe digital camera formats.

Realizing that there is now an entire generation entering the photographic community who never experienced film-based photography, let's start with a short history of the terms that were essential to film-based photography at the time digital photography came on the scene.

The three "flavors" of film

In the mid-1990s as digital cameras were beginning to enter the market, traditional photographers were choosing between three primary types of film:

• Transparency film (sometimes called slide film) -- pictured at top
• Color negative film for producing color prints -- pictured in center
• Black and white negative film -- shown at bottom.

Each film had (and still has) its own purpose as well as its own set of technical specifications and issues. Many of the terms that deal with these purposes and technical considerations have carried over to digital photography:

• Grain and noise -- Originally, grain was used to describe the visual, almost sand-like, appearance induced by the individual silver or color dye particles that made up the image. In the case of film, the higher the ISO rating on the box of film, the more apparent became the grain in the print or slide -- because the physical size of the silver or color dye particles is larger in higher ISO films. Today, grain is still heard, but now it describes the electronic noise (grain) seen in a picture that is caused by the digital sensing unit, becoming noticeably more distracting as ISO settings are increased.
  
• Sharpness and resolution -- Each film had its own sharpness and resolution characteristics. Lower ISO films produced images with more apparent sharpness and could be enlarged to larger print sizes with minimal sacrifice in sharpness (or resolution). In a digital camera, sharpness is not only a function of lens focus but also of the quality of the sensor and its megapixel count -- very similar to those film considerations.
• Film -- Even the term film is used in today's digital cameras as a way of describing data storage cards (i.e., digital film) as the resting place for the completed image inside the camera.
  

In terms of the 3 types of traditional film, digital photographers no longer have these restrictions. It's probably most accurate to equate today's digital camera's image to slide or transparency film. The first image we see is a color positive -- just like a slide or transparency film. We no longer have a need for a negative. In the case of black and white, we can easily convert the digital camera's color image to a positive black and white image in seconds.

Film Size

In film-based photography, the physical size of the film is extremely important to the quality of the image. In the film environment, 3 film/camera formats are most often cited -- 35mm, medium format, and large format.

35mm black and white negative

Shown above is a 35mm black and white negative. The dimensions of the negative image are 36mm x 24mm. For decades, this has been the standard 35mm format and gave birth to the worldwide acceptance of 35mm camera as a viable professional and serious amateur format. The cameras that use 35mm film are small, adaptable to many types of photographic assignments, and produce high quality images within certain enlargement parameters.

But there are demands in photography for even higher quality and higher resolution images. This is especially true in professional commercial photography where detail, color saturation and shadow detail are critical, and where very large enlargements are frequently requested.

Medium format (2 1/4" x 2 1/4")

For these photographers, a popular choice is a medium format camera that uses larger roll size films. Pictured above is a medium format (2.25" x 2.25") black and white negative taken with a Hasselblad camera -- the astronaut's moon camera. This format yields a negative or transparency that contains over 3 times the image area and information as its 35mm cousin. As a result, the images produced from medium format camera are usually sharper, contain more detail, and can be used to produce even larger prints of exceptional quality. The trade off is that camera using these larger roll films are larger themselves, and may not contain the degree of automation seen in many pro 35mm cameras.

35mm vs. Medium format

Here's a "to scale" side by side comparison of 35mm film format to the larger medium format negative. It should be apparent that the larger the negative, the more image information is available and the less enlargement is required to produce "same size" images than from a 35mm negative.

This same image quality relationship still exists in today's digital cameras. For example, Hasselblad also manufacture digital versions of their cameras. But because of the size of the sensor in these cameras, the image pixel count is 30MB or greater. Again, just like traditional film, this larger sensor provides larger files which yield greater image detail, more information in the high and low densities and an ability to produce larger prints of exceptional quality.

Large format cameras use film in cut sheet form. These individual pieces of film can range in size from 4"x5", 5"x7", 8"x10" and greater. As you can imagine, film of this size produces the ultimate image sharpness, color clarity and quality at even the largest print sizes. Because of the size of the cameras that use large format film, they are almost always mounted on a tripod. But, they are a mainstay in many segments of professional photography (product photography, landscape photography, industrial photography, architectural photography, etc.)

There are two format terms that have become unique to digital photography -- DX and FX.

The DX and FX views of the world

Most of today's DSLR cameras do not cover the same area as a traditional 35mm film frame. Nikon uses the letters DX to designate this fact. The entire picture area shown above represents an image from a traditional 35mm camera. This is what is seen through the viewfinder as the picture is being taken. For the purpose of this example, I'll say this picture was taken using a 55mm "normal" lens. The green box shows the portion of the same scene that would be captured by most of today's DSLRs (DX cameras) using the same 55mm lens. The DSLR captures significantly less of the scene than the traditional 35mm film camera using exactly the same 55mm lens. This choice was made by camera manufacturers because of technology limitations at the time DSLRs were first introduced and the economics involved in producing "full frame" sensors.

The ramifications for 35mm photographers are obvious. Their lens collections suddenly became restricted. What was once a normal lens on their camera now became slightly telephoto when used on their new digital cameras. Their tremendously wide angle lenses became much less wide. Camera manufacturers responded in two ways:

• New lenses in the focal lengths professionals now needed to do their work
• New sensors that covered the entire traditional 35mm frame (designated FX for "full frame").

There's good and bad news associated with both of these developments. New lenses require a significant investment. And the now emerging FX cameras are the most expensive cameras available.

Undoubtedly, the cost of FX cameras and the sensors that make them possible will decrease over time. But don't wait for a cheap FX format camera to show up at Best Buy before jumping into digital photography. It's going to be quite some time.