Macrophotography in the Field
Written by Sanford Weiss   

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In this photo, notice how the flash was placed to the left of and oblique to the subject. A suitable scale was placed to the side of the subject to enable easy visual determination of size.

FORENSIC DOCUMENTATION often requires photographing objects such as blood spatter on walls; footwear impressions in sand, mud, or snow; or innumerable small objects on the ground, in the grass, inside a bush, or under a car—in the bright sunlight or the middle of the night. Sometimes it is the smaller aspects of larger objects that serve as the evidence.

None of these scenarios are especially easy to properly document. The photographer must be creative, spontaneous, and, above all, well prepared to enable the proper capture of images of these types of subjects with a reasonable degree of accuracy.

All evidence should be photographed in place—or in situ (as discovered)— prior to collection and transport to the laboratory for further documentation and study. Photographing the location, orientation, situation, and relationship of an object within the scene as a whole is just as critical as photographing close-ups of the evidence itself. Sufficient images must be captured by the photographer to enable subsequent correlation between the images and the investigator’s notes.

Every agency’s best-practice documents or standard operating procedures should specify the amount of macro detail of evidence that needs to be captured in the field. Detailed study of small evidence may not be possible until the evidence has been transported to a remote location such as the laboratory. The documentation of large objects of evidence—a crashed automobile, for example—must often be completed down to a macro level in the field. Photographing a scene in this kind of detail sometimes involves other issues or difficulties, including time constraints.

Something small—either a small object or a small part of a large object—may be contributory to the root cause of an incident and should be documented in situ, even in the largest disasters. Sometimes the small object of evidence is a critical part of a scene that cannot ever be moved to the lab. Skid marks on a roadway, paint scrapes on a telephone pole, bullet holes on a building facade, and any other type of similar evidence must be fully documented in situ because it cannot be moved and will change over time.

The determination of how big an object of evidence needs to be before it is considered too large to be removed or collected is another aspect that must be detailed in departmental best-practice documents.

For example, if a large section of drywall is covered in blood spatter, will your department start cutting to take the section back to the lab—or will you simply photograph the blood spatter in place? This question should be answered by well-documented standard operating procedures.

Small Evidence


This image was exposed with a ring-flash on the camera to reduce harsh shadows that could be caused by the high ratio of subject relief to subject size.


Note the distorted filament inside this car headlight. This indicates that the low beam of the headlight was in operation when the vehicle encountered an obstruction. It was not possible to use a scale on the image so the magnification had to be calculated. (The use of a rubber lens hood on the lens during the exposure kept flash reflections to a minimum.)


You should keep a collection of accessories in your kit to enable images of difficult aspects of complicated evidence.

The documentation of small evidence in the field should be performed, time permitting, according to accepted best practice, including:

  • Overall photographs of the location of discovery;
  • Mid-range images to document orientation and relationship of evidence to the scene and to other objects of evidence at the scene;
  • Close-up images to characterize the evidence in relation to its discovered location;
  • Macro images to document the evidence itself if it is critical to characterize the evidence before it is relocated, or if the evidence is a part of a scene that cannot be moved.

Include appropriate scales and references in images to enable post-process sizing and placement.

Small marks and colorations may be the key to an investigation. Some-times a key image will show small scratches and other toolmarks or witness marks (punch marks or scratches used to position or locate characteristics for comparison) on an object. Successfully photographing these details can be complicated by shiny surfaces where reflections are common, or by shadows cast by other parts of the subject.

Documentary images must be technically accurate—not necessarily aesthetically pleasing. To illustrate the characteristics of evidence, the forensic photographer must be able to create accurate representations in images by the selection and use of the most appropriate photographic hardware and lighting, even if the finished photographs are not “works of art”. Do not attempt to create pleasing compositions or add objects or backgrounds to eliminate distractions. Those kinds of images should be captured in the lab or studio.

Macrophotography Equipment

Macrophotography is the type of close-up photography in which the final magnification of the image of the subject is anywhere from about .5x to about 25x life size (also denoted as 1:1). This type of photography is useful for close inspection or ease of demonstration. Macrophotography fits the niche between normal photography and microphotography. Documenting evidence in situ is performed using a camera with a close-up (macro) lens, or using a camera with appropriate close-up accessories and an electronic flash unit (EFU).

A variety of lighting techniques and formulas may be used to properly illuminate macro subjects. Light must reflect off of or pass through a subject to capture its image. In either case, the light must be controlled in both intensity and direction or location in relation to the evidence to limit shadows, emphasize textures and landmarks, and achieve proper exposure to supply the most accurate images.

Several kinds of photographic hardware are commonly used for creating the required magnification and exposure including the following:

  • Macro-lens equipped camera
  • Close-up (diopter) lenses
  • Extension tubes
  • Extension bellows
  • Lens reversing rings
  • Accessory lighting

Two of the greatest challenges in macrophotography are the inherent lack of depth of field (DoF) when the camera and lens are close to the subject, and the determination of the proper lighting to either avoid or create shadows. Shadows may hide or accentuate necessary bits of information, depending on where they are and the character of the material being photographed.

Macrophotography in the Laboratory

Macrophotography may be undertaken in a laboratory, studio, warehouse, morgue, or other place where evidence has been moved. In these cases, the evidence must be properly protected but may be handled, set up, lit for proper exposure, put in front of a suitably colored background, and subjected to inspection and documentation, using all available equipment and techniques. The photography may be tedious, exacting, and require skill and experience of the photographer.

About the Author

Sanford Weiss is the author of a book published in 2009 by Pearson, Prentice Hall. The title of the book is Forensic Photography: The Importance of Accuracy. Weiss can be reached at any time by e-mail: This e-mail address is being protected from spam bots, you need JavaScript enabled to view it

WEB-EXCLUSIVE MATERIAL

Magnification

One of the more confusing aspects of macrophotography occurs when someone asks the photographer or witness at trial to tell the court the magnification represented by the images of the evidence. It can be very embarrassing when that information is difficult to determine. Here are some formulas that can help you come up with the right answers.

Magnification (M) is the relationship of subject size to image size on the film or electronic image sensor. The magnification of the image is used to determine the reproduction ratio of the image to the subject.

Reproduction Ratio (RR) = the size of the image/the size of the subject.

M may be expressed in three ways:

1) As a ratio, image size to object size. Example: 2:1
2) As a multiple. Example: x 4, x 1.0, or x 0.5
3) As lens-to-subject distance (u) and lens to image distance (v).

Example:
M = v/u = image distance/subject distance
1/u + 1/v = 1/F or v = (M + 1) F (where F is the focal length of the lens)

Magnification will change when the focal length of the lens or the lens-to-image distance changes. Therefore, magnification can change by adding extension tubes or diopters.

Example:
RR for a 50mm lens and 10mm extension is 1:5, or .2x

TIP: Magnification may be mathematically calculated by dividing the focal length of the lens into the length of the extension.
Magnification = extension/focal length
Example:
When using a 50mm lens on a 40mm tube, the magnification will be .8x life size.

Close-up Diopter Lenses

RR of 50mm lens with close-up diopter lenses:
50 mm with +1 lens = 1:20
50 mm with +2 lens = 1:10
50 mm with +3 lens = 1:6
50 mm with +4 lens = 1:5

When adding close-up lenses to increase magnification:
Magnification = focal length of lens/focal length of diopter
Example:
If an image of a 4-inch subject is .5 inch on sensor, the RR is 1:8
RR = .5 inch / 4 inch = 1:8
If an image of a .5-inch subject is .5 inch on sensor, the RR is 1:1
RR = .5 inch /.5 inch = 1:1

Extension Tubes or Bellows

Using extension bellows between the camera body and the lens is another way to gain magnification by extending the distance between the sensor and the lens. Bellows are similar in purpose and operation to extension tubes. Bellows provide variable extension and, therefore, variable magnification. They are available for any interchangeable-lens SLR camera. The minimum and maximum extensions are determined by the construction of the bellows. The magnification is computed by dividing the lens focal length into the extension.

Magnification = extension/focal length
RR for a 50mm lens and 20mm extension is 1:2.5, or .4x.
RR for a 50mm lens and 50mm extension is 1:1, or 1x.
Example:
If using a 50mm lens on a 200mm bellows, the magnification will be 4:1 on the image plane.
200/50 = 4
Exposure Increase (EI) for Lens Extensions
EI = (lens focal length + extension/lens focal length)2
Example: A 50mm lens with a 25mm extension:
EI = (50 + 25/50)2
(75/50)2 = 2.25 X E = 1 1/3 f-stops increase
1.4 X E = 1/2 f-stop
2 X E = 1 f-stop
2.9 X E = 11/2 f-stop
4 X E = 2 f-stop

TIP: Using sufficient extension to raise the magnification to life size (1:1 magnification) requires two extra stops of light.

Scale

Scale = linear size of image/linear size of subject
Example:
If an image is 8 inches wide and the subject is 1 inch wide, the scale of the image is 8/1 = 8x = 8:1.
Example:
If an image is 1 inch wide and the subject is 1 mile wide, the scale of the image is 1 inch = 1 mile.

TIP: Remember to include color references in at least one image of each piece of evidence when color accuracy is an important part of the evidence.

TIP: When exposing macrophoto-graphs, the camera should be oriented as close as possible to perpendicular to the widest plane of the subject, unless accessory lighting is used and the surface of the evidence is reflective. In these situations, move the camera or the flash to slightly oblique to the widest plane of the object so the flash reflection does not re-enter the lens and create a hotspot. Auto-exposure capabilities of the camera should not be disrupted.

TIP: The use of a neutral colored background is recommended. Red paper put behind the subject creates aesthetically pleasing images but large red areas in a group of images may be psychologically displeasing to the court.

TIP: Remember to multiply image magnification by the size of the courtroom display to determine the actual magnification of the image from the actual subject.


ORIGINALLY PUBLISHED:
"Macrophotography in the Field," written by Sanford Weiss
November-December 2009 (Volume 7, Number 6)
Evidence Technology Magazine
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