Robinson Introduction to Crime Scene Photography

1. Auflage 2012
ISBN: 978-0-12-386544-1
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: Adobe DRM (»Systemvoraussetzungen)

E-Book, Englisch, 432 Seiten

Introduction to Crime Scene Photography acquaints the reader with the essentials of basic crime scene photography techniques. It looks at the concepts related to composition and relates them to the types of photographs captured by crime scene photographers. It explains how to capture images based on the exposure settings chosen to produce the effect desired. It considers the techniques used needed to control and maximize Depth of Field (DOF), and reviews how the different lenses will affect an image. Organized into seven chapters, the book begins with an overview of crime scene photography and composition, including the three cardinal rules of good photography. It then proceeds with a discussion of the benefits of bounce flash and how to utilize this technique to properly compose the subject of interest. It also explains how to capture any image necessary at the crime scene by combining the concepts of composition, nonflash exposure, DOF, flash exposure, and the use of various types of lenses. In addition, the reader is introduced to various energy sources and filters, digital processing of evidentiary photography, and legal issues related to photographs and digital images. Examples and illustrations are provided throughout to demonstrate how the concepts examined tend to form a sort of symbiotic relationship. This text will benefit scene investigators and photographers, forensic consultants, forensic scientists, undergraduate students in forensic and/or criminal justice programs, law enforcement professionals, and anyone who wants to acquire the skills needed to be a successful crime scene photographer. - Contains over 350 high-quality 4-color images - Rules of Thumb are included to highlight key concepts

Edward M. Robinson began his career in law enforcement in 1971, with the Arlington County (Virginia) Police Department (ACPD). After 25 years with the ACPD, Mr. Robinson created the Crime Scene Investigation concentration at The George Washington University for their Master of Forensic Science degree program, and continues there today.

Autoren/Hrsg.

Robinson, Edward M.

Leseproben

Chapter 2
Exposure
Contents
The Proper Exposure Triangle Exposure Stops Exposure Variables Reciprocal Exposures The Reflective Light Meter Normal Versus Non-normal Scenes Tools for Determining Proper Exposures with Tricky Scenes Exposure Modes Bracketing The F/16 Sunny Day Rule Common Filters Chapter Summary Learning Objectives
Upon completion of this section, you will be able to: Explain the four exposure variables and their interrelationships Explain that shutter speeds are not only exposure controls but also motion controls Explain the concept of the Theory of Reciprocity Explain how a reflective light meter works Explain what “tools” are available to help determine the proper exposure for a tricky scene Explain the typically encountered “non-normal” scenes that require exposure adjustments Explain the various exposure modes available with different cameras Explain how to bracket in manual and automatic exposure modes Explain the F/16 Sunny Day Rule Explain the basic uses of filters as lens protection, reflection removers, and “sunglasses” Key Terms
Aperture Aperture Priority exposure mode (Av) Bracketing Burning and dodging Diaphragm Digital noise/dark noise Dirty snow Exposure compensation Exposure latitude Exposure stops Fill-in flash F/stop F/16 Sunny Day Rule Graininess 18% gray card Manual exposure mode (M) Neutral density filter Polarizer filter Polarizer filter Program exposure mode (P) Reflective light meter Shutter Shutter Priority exposure mode (Tv) Theory of reciprocity UV filter White balance The Proper Exposure Triangle
Images can be considered properly exposed, overexposed, or underexposed. For the most part, it should be a goal to have most images properly exposed. Why just “most” of our images? There will be times when we intentionally “bracket” a particular image. To bracket an image means that after taking what we consider to be a properly exposed image of a particular subject, we immediately take two or more additional shots of the same subject from the same point of view; these additional shots are intentionally overexposed and underexposed. Usually, there are two good reasons for following one photo with a series of brackets, as are shown in Figures 2-1, 2-2, and 2-3. FIGURE 2-1 A +1 bracket FIGURE 2-2 Properly exposed FIGURE 2-3 A –1 bracket One is that the lighting at the scene might be particularly problematic for any number of reasons, and we are actually unsure if our exposure setting on the camera will truly produce a “proper exposure.” In this case, it is just being smart to take additional exposures, in the hopes that at least one of them may truly be “properly exposed.” Think of it as taking “insurance shots.” We won’t get the opportunity to capture this image of the subject ever again, and we want to be assured that at least one of this series of bracketed shots has a properly exposed image among them. Another good time to take a series of bracketed shots of the same subject is when that subject is a candidate for examination-quality images. As discussed in the previous chapter, these are extremely important images that will be either analyzed or examined in a forensic laboratory by an expert who will be comparing the image to something else to try to establish identity. For example, an image of a fingerprint from the crime scene will be compared to known fingerprints from a suspect. Or an image of a shoe print from the crime scene will be compared to a suspect’s shoe. Or an image of a bite mark on a victim will be compared to the known dentition of a suspect. In these situations, it is extremely important that the examiner be able to distinguish all the details in the image. Even if the image is “properly exposed,” some of the details necessary to make the identification may be in an area that is a bit more brightly lit than the rest of the image. Additionally, some of the details necessary to make the identification may be in an area that is a bit less brightly lit than the rest of the image. In these situations, in order to provide the best opportunity for the examiner to clearly distinguish all the markings within the image that are there, having additional brackets of the “properly exposed” image might help ensure that the examiner can see all that is present in the series of images necessary to make the determination of either an identification or an exclusion. Exactly how to change the exposure settings to capture a series of brackets of an important item of evidence will be explained immediately after the exposure variables themselves have been explained. There are four variables that affect an image’s exposure: The f/stops The shutter speed The ISO setting The lighting at the scene that affects the subject of our image: the ambient lighting at the scene or the lighting we choose to supplement the ambient lighting with, be that an electronic flash, a flashlight, an alternate light source (ALS), or any other lighting to supplement the ambient lighting If any of these four variables changes, the exposure of the image is changed. To help us remember the four variables that affect an image’s exposure, we group them into what is referred to as the proper exposure triangle. Although a triangle has just three sides, adding the “inside” of the triangle as an element of proper exposure practices allows us to group these four variables together. A typical proper exposure triangle looks like this: FIGURE 2-4 The proper exposure triangle Exposure Stops
Before discussing the individual exposure variables, it is best to understand gross exposure changes first. An image may be described as being properly exposed, overexposed, or underexposed. Of course, any one of the three can happen accidentally, or they can happen because the camera’s exposure variables were carefully chosen to create that effect. When intentionally choosing to alter the camera’s exposure, it is possible to increase or decrease the exposure by precise amounts. When we discuss exact exposure amounts, the first concept to understand is the idea of an exposure stop. It is possible to take any properly exposed image and to increase its exposure by precisely one stop or decrease its exposure by precisely one stop. A +1 exposure stop means that you’re doubling the lighting of the original image. A –1 exposure stop means that you’re halving the lighting of the original image. You may hear a photographer talk about “opening up one stop,” or “increasing the exposure by +1.” Conversely, you may hear that they intend to “close down one stop,” or “decrease the exposure by –1.” Many years ago, cameras offered the photographer controls that altered exposures only by a full stop. Today’s cameras, both film and digital, usually allow a photographer to vary exposures by different incremental amounts. Most cameras today include menu selections to change exposures by full stops, 1/2 of a stop or 1/3 of a stop. This point is very important to remember, because depending on how the camera’s menu has been set, changing a camera’s exposure by pushing a button or rotating a dial may result in either a full stop alteration with just one push of a button or one click when rotating a dial—or pushing the same button once or rotating the dial to the next click may only be a 1/3 stop or a 1/2 stop adjustment. You might be trying to increase or decrease exposure by +1 or –1, but if your camera has been set previously to provide 1/2-stop increments or 1/3-stop increments, one push of a button or one rotation click of a dial may not provide you with a full stop change. The solution is to check your camera’s menu selections, especially if the camera you are using has been used by another photographer who prefers different increments of bracketing. Exposure Variables
Now that you understand how an exposure can be altered in precise amounts with both overexposures and underexposures, it is now time to learn how this information applies to each of the exposure variables. Shutter Speeds as an Exposure Variable
The shutter of a single-lens reflex (SLR) camera lies just in front of the film or digital sensor. For this reason, the shutter of an SLR camera is called a focal plane shutter. In other camera systems, the shutter might be located in the lens instead of the camera body. The shutter covers the sensor until the shutter button is depressed, when it will open and allow light coming in through the lens to strike the sensor for a predetermined amount of time. The times the...