Technical Aspects of Photo-Documentation and
Capturing Aesthetic Geological Subjects in the Field
By Cleet Carlton
Poster session presented at the Geological Society of America, Rocky Mountain Section
55th Annual Meeting (May 7-9, 2003) in Durango, Colorado
Links to examples and additional text (in green) used in the poster session have been included.
Photo-documentation and capturing the aesthetic features of geological subjects can be enhanced with attention to several basic rules of photographic technique. Major factors to be considered include lighting, color, and photographic composition.
Lighting of geological subjects for both documentation and aesthetic purposes includes the incident angle of sunlight (or other illumination source), brightness, and contrast. The angle of the light source is most important in how details on surfaces (e.g., exposed bedding planes, etching, sole marks) are captured. Example 1: Angle of Light Source, Mesquite Flat Dunes in Death Valley
Brightness and contrast need to be adjusted to record pertinent details on film/digital file for photo-documentation. Brightness is typically adjusted through the combined reciprocal effect of aperture and exposure time, within the range of application of a particular film speed (or digital camera rating equivalence). The contrast between the lightest and darkest portions of the image is controlled by exposure settings and film type, and can be modified in post-processing through the dodging/burning method either in the darkroom or on the computer.
Opening the aperture (lowering the F-stop) allows more light to enter the camera but reduces the depth of field. This allows for a shorter exposure time, which may be beneficial under low light conditions or to freeze motion (as a result of wind action, for example), but may limit the area that can be kept in focus. If an increased depth of field is required to capture the subject in focus, an increase in film speed is required to maintain a short exposure time. In the field, a decision should be made whether to attempt to capture highlight details, shadow details, or both (if possible). If limitations in contrast are acceptable (or preferred for dramatic purposes), spot light metering is a useful tool to establish the correct aperture/exposure time settings for a specific target. For many aesthetic purposes and photo-documentation, capturing detail in the widest range of light conditions is typically preferable. Film type is the initial limiting factor. In general, negative films have a wider latitude (ability to register details on film over a range of light conditions) than slide films, and are preferable for these purposes. However, since highlight and/or shadow details may be compromised due to the limitations of all but the most expensive post-processing devices (scanners and printers), the required final output media should be taken into consideration. Another lighting decision, which can be made in the field or planned ahead of time, is whether to isolate the object of interest (spotlighting). Example 2: Spotlighting, Landers Earthquake Scarp
When color photography is employed, the purpose of attempting to capture "true" color or to represent the image with color enhancement should be established. A subject in the field has intrinsic color, which is modified by nature of the light illuminating it. Unless a physical sample of the subject is collected or a comparative reference (like a color chart) is used during the taking of the image, and the illuminating light can be recreated to compare the sample or reference to the image output, an interpretation will be required to estimate "true" color, irrespective of film type. Example 3: The Concept of "True Color" and the Myth of Slides verses Negatives
Estimations of color may be enhanced by knowledgeable reference to as many diverse features in the image (color of sky, water, specific rock types, animals, vegetation, or human skin tones) as possible. Example 4: Color References, International Space Station over Bridalveil Falls
However, under low light or high contrast conditions, it may be difficult, if not impossible, to correct for color across the entire range of brightness. For example, in very low light conditions (e.g., twilight), a shift in color to the blue side of the spectrum is typical, particularly in the shadow details. Example 5: Blue Shift in Shadows
In traditional (non-digital) photography, color enhancements are achieved through the film type specifications (saturation, film for certain artificial lighting conditions), and darkroom manipulations (dodging/burning, color adjustment), and are specific for each printing medium. Additional enhancements are achieved on the computer (scanned film/digital image).
Photographic composition concerns the overall positioning of the elements in the image, including angle, distance, centering, and juxtaposition.
Lens types (normal, wide-angle, telephoto, zoom) are the initial tools for composition. Crosshairs on the lens are useful for adjusting horizons and vertical features. A tripod is also useful to maintain control of the image angle, especially with increased telephoto distance or when multiple exposures are required along a straight transect. Centering a subject may be most useful for photo-documentation, but not necessarily for aesthetic purposes. For photo-documentation, size and scale of objects in the image are usually important to note. This is often accomplished by the placement of a scale or recognizable item (e.g., rock hammer, compass) adjacent to the object. An option, which may be preferable for aesthetic purposes, is to measure and note the dimensions. Photo-documentation may require the capturing of the maximum detail technically possible, most accurate color representation, and a composition that shows the necessary relationships of all the pertinent objects, including sizes, angles, and distances. Aesthetic images may also require the maximum technically possible detail or can be selective in focus, achieve accurate color representation or receive color enhancement, and may benefit from all of the aforementioned compositional factors.
Example 6: Composition #1 - Sea Level at Badwater, Death Valley
Example 7: Composition #2 - Evidence of Glaciation, Yosemite National Park
How lighting, color, and photographic composition can be best approached depends on the purpose and the final output of the image. The final output may be reflective media (paper, polyester), transparencies, and/or digital files. The final or maximum image/file size, and the technical quality requirements are key in determining the best method for obtaining the image.
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