High Resolution and High Definition

In a nutshell: 

  • "Resolution" describes a physical state

  • "Definition" is an aesthetic choice.

Image sharpness is by no means a requirement for excellent photographs. It is one of many aesthetic choices that a photographer can make.

When sharpness, fine detail, and a full contrast range are the aesthetic goal, the photographer has three tools available that offer a surprising amount of control. Of course, the photographer must use his or her camera correctly, so that camera shake and lens flare do not intrude. Then it is

  • film choice, 

  • developer choice, and 

  • processing technique 

that largely dictate image sharpness.

Sharpness, and the illusion of sharpness, result from the resolving power of your negative material and the rest of your optical system (including the lenses in your camera and enlarger), and your processing methodology. The two key concepts are 

  • image resolution, and 

  • image definition.

“Image resolution

This term describes image sharpness achieved by maximizing the ability of the film to record image detail.

Image detail can be lost in two ways. 

  • First, all optical systems are by their nature limited in the detail they can resolve. These limitations are dictated by the laws of physics, which dictate that light is not only focused by lenses, but also refracted (scattered) by the same lenses. 

  • Second, films have granular properties which limit the detail they can record.

High-resolution films have inconspicuous or invisible grain, when correctly processed. They achieve high resolution by minimizing the detail lost due to grain. They cannot compensate for resolution losses elsewhere in the optical system.

Grain is a function of the film's physical characteristics, and of the developer and processing technique used. 

  • Some developers and techniques accentuate the grain on fine-grain films. 

  • No developer or technique can give fine grain on coarse-grained films.

Grain size, film speed, and film contrast are related. A high-resolution film will necessarily have 

  • small grains, 

  • high inherent contrast, and 

  • relatively low sensitivity (low speed). 

Conversely, a high speed film will necessarily have 

  • larger grains, 

  • lower inherent contrast, and 

  • low resolving power. 

These relationships are dictated by the laws of physics which describe how light reflects from sub-microscopic particles of differing sizes.

Maximum resolution, reasonably high speed, and a full range of pictorial contrast can only be achieved with high-resolution films through the use of specialized developers. 

 Image definition

This term applies to an image in which the edges of fine detail are sharply distinct. Such an image is said to have prominent microstructure and exhibit "high acutance."

It may or may not have prominent grain. 

Microstructure is influenced more by choice of developer and development technique than it is by choice of film. Any black and white film can be developed for acutance, but not all developers are suitable.

Coarse-grained films developed for high acutance give the illusion of sharpness, even though close examination reveals that detail is indistinct. The visual effect can be quite stunning.

Fine-grained films developed for high acutance often give the appearance of striking clarity.

High definition (in other words, "high acutance") images are obtained with a special development technique. This technique was first promoted by the very inventive German photographer and photochemist Willi Beutler (1903-1978) in the middle of the 20th century. It is essentially an agitation technique which includes periods of time in which image density is allowed to build up at the edges of grain aggregations, such that the image has sharply defined edges at the microscopic level.

Beutler called this "compensating" development. It is most effective when practiced as an agitation regime, for example, you might agitate for five seconds, then allow the film to sit for three minutes. Exact timing depends on the specific film and developer being used, but the compensation principle applies: the edges of the image's granular microstructures become sharply defined.

Maximum definition can be carried too far, creating bizarre images (which may, of course, be exactly what a creative photographer has in mind). When practiced carefully, with appropriate films and developers, the Beutler "compensating agitation" technique creates images of extraordinary brilliance and clarity.

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