Field of View

If all of the images made with single focal length cameras disappeared, the loss would be catastrophic. Even with interchangeable lenses, many of the greatest photographers have chosen a "favorite" focal length, with which most of their most notable images were made. The focal length(s) of the lenses available to a photographer at any given time greatly affect the selection and management of the image. One either adapts the image to the focal length or the focal length to the scene. The ability to change the focal length, either by changing lenses or the use of a zoom lens, frees the photographer from a major constraint, but it also complicates the image management process by adding an additional element to the selection process.

These scenes, both "full frame", were taken from a narrow ridge which limited movement with authority! Had the Minox been the sole photographic instrument, the more moody and representative image would have been missed. It is illustrative of the fact that there is a proper tool for every situation, and the Minox is not a universal photographic instrument. In fact, access is the controlling element here, prohibiting establishment of the near-far relationship with the Minox. Were it possible to move lower to include the near roof, the Minox might have been useful.

35mm camera with 28mm lens

Minox 15mm lens (~48mm lens on a 35mm camera)

Lens Focal Length
The "Normal" lens

Using the Leica Manual as a reference, the focal length of a lens is defined as the distance from the principle plane (optical center) of a lens to the film "when the lens is focused on a subject at an infinite distance."

The focal length of a "normal" lens, one which provides approximately the angle of view of the human eye, is equal to the diagonal of the negative. If less than the entire negative is used during printing, the calculations must reflect the new effective negative size. The effect can be best seen in the 6X6 cm (Rollei, Hasselblad, etc.) data which reflects the relatively severe (20%) cropping to a 4:5 ratio which leads to a reduction of the effective "normal lens" from 79.9mm to 72.4mm. The result is to shift the standard 75mm Rollei TLR lens from slightly wide-angle to slightly long.

Depth of Field, the near-far range of acceptable sharpness ON THE PRINT, depends on

  1. the focal length of the lens,
  2. the aperture used, and
  3. the enlargement factor of the print

Since larger format cameras require longer lenses for a "normal" view, smaller apertures are required to achieve a given depth of field. The following table provides a glimpse of the relationship between the three factors listed above.

 

During the development of this thread, I became curious about the focal length of the lenses used for some of the memorable images made by Ansel Adams. A random search of his The New Ansel Adams Photography Series yielded the following short list. Because various negative sizes are involved, I included a list of "equivalent" 35mm and 6x6cm lenses. To further complicate the issue, I assumed the prints made from the 35mm and 6x6cm negatives would be cropped to the 4x5 ratio. Please do not nitpick the calculations, the object was to provide a feel for the focal lengths used by one photographer in a variety of situations. It was interesting to me in that the range is relatively limited, generally within a 2:1 range, and well within the limits of today's high quality 35mm zoom lenses. DO NOT interpret this as an endorsement for the use of 35mm as a substitute for larger formats!

RETURN HOME