Forensic Photography Lecture Notes

Course Overview - FIVS 210: Forensic Photography

  • Instructor: Professor Shelby Kmidowski Moran

Key Camera Terminology

  • Types of Cameras:

    • SLR (Single Lens Reflex)

    • DSLR (Digital Single Lens Reflex)

    • DSLM (Digital Single Lens Mirrorless)

  • Camera Components:

    • Pentaprism, Eyepiece, Film Plane, Focal Plane Shutter

    • Examples of models: Nikon D800, Canon 200

Camera Nomenclature

  • ISO Speed:

    • Defined as the measure of sensitivity of the camera’s imaging sensor to light.

  • Controls on Camera:

    • Set Button, Main Dial, Power Switch, Mode Dial, Built-in Flash, AF-assist Beam, Shutter Button, Red-eye/Reduction Self-timer Lamp, Dioptric Adjustment Knob, and others.

    • Back of Camera :

    • Face of Camera :

Essential Camera Functions

  • Menu Controls:

    • Options including Image Quality, ISO settings, Flash Control, and Beep settings.

  • Diopter Adjustment for Viewfinder:

    • Adjustment allows photographers to see clearly through the viewfinder based on an individual’s vision.

Memory and Storage

  • Memory Cards:

    • Types include CompactFlash and Secure Digital High Capacity (SDHC) Cards.

  • Battery Specifications:

    • Importance of ensuring battery and memory storage are managed correctly.

Lenses and Filters

  • Zoom Lenses:

    • Used for convenience, emergency, versatility; specific examples include Nikon DX AF-S NIKKOR 55-200mm.

  • Camera Filters:

    • UV Filters for lens protection, haze reduction, and warming.

    • UV Filter:

    • Polarizing Filters for enhancing color and reducing glare.

    • Polarizer:

Understanding Optical Distinctions

  • Normal Lens (50mm):

    • Specific focal lengths for different formats to maintain image integrity, with details on various formats.

Fundamental Terms

  • Exposure:

    • The amount of light reaching the camera sensor which creates visual data over time.

  • Exposure Stops:

    • Changes in the original exposure that either halve or double light intensity.

  • Depth of Field:

    • Defined as the distance between the nearest and furthest objects in “acceptably” focus.

  • ISO:

    • A camera setting that measures the level of the sensor’s light sensitivity.

Perspective in Photography

  • Normal lens focal length for sensor format produces the most accurate “picture” or reality

  • WHY IT IS IMPORTANT:

- Do not want to produce any warped of distorted images that impact the validity/accuracy of the crime scene OR piece of evidence.

- MAIN PICTURE GOALS: The photograph production should be replicated as if you are viewing the crime scene in person.

Lenses Note:

  • Certain cameras will only obtain zoom lenses, because of this, it is important to ensure awareness of the focal lens length

  • Only use wide angle and telephoto focal lengths when necessary

Inverse Square Law (*)

  • Description:

    • The law describes how light intensity decreases as distance from the source increases.

    • Inverse proportional relationship

  • Quantitative Impact:

    • If the distance is doubled, the intensity of light is quartered

    • If the distance is halved, intensity of light is quadrupled.

  • Practical Example:

    • Changes in exposure settings (sun, street lamp, flashlight) as one moves further or closer to a light source.

    • Main takeaway: The larger the distance is from the light source, the smaller/decrease there is of light to be able to reach you.

Exposure Variables

  • Four main variables affecting exposure:

    1. Shutter Speed

    2. Aperture

    3. Film Speed/Digital ISO

    4. Ambient Lighting of scene of lighting that can be used

The Exposure Triangle

  • Components:

    • ISO, Aperture, Shutter Speed

  • Visual Representation:

    • More Noise = Brighter

    • More Motion Blur = Brighter

    • More Shallow DOF = Brighter

NOTE^: The opposite of these parameters is still proportional. Example : Less Noise = Less Brighter/Dimmer

  • Noise

    • Definition of noise in photography and its relation to high ISO settings

F-Stop Mechanism

  • Definition:

    • The f-stop number is calculated as the focal length divided by the diameter (D) of the lens opening: f−stop=fDf{-stop}=\frac{f}{D}

  • Impact on Depth of Field:

    • Explains how varying f-stop settings influence depth of field and artistic choices in photography.

The Importance of ISO Numbers

  • Purpose of ISO: The setting provides information on how sensitive the camera is to light.

  • ISO Range:

    • Typical ranges: 100 to 3200, relevant to both film and digital photography.

    • A low ISO value (i.e 100) means that there is LESS sensitivity to light which PRODUCES a clearer (higher resolution) image.

    • A high ISO value (i.e 3200) means that there is more sensitivity to light which PRODUCES a grainy image. Note: This also means it works better in the dark.

Summary on range:

  • Low ISO produces clearer images; higher ISO better for low light but results in graininess.

  • Forensic Aim: We want to produce examination quality images which correlates with a low ISO value of 100.

  • ISO Numbers (cont.) :

18% Grey Card

  • Function:

    • A tool for used to reduce black noise in digital cameras and set more accurate exposure & white balance.

  • What is it:

- Flat card reflecting 18% of light falling on it, hence showing the grey tone.

  • Digital cameras are already calibrated to assume that the average scene will reflect 18% of the light present.

Shutter Speed Dynamics

  • Definition:

    • Refers to the time the shutter remains open.

  • Speed Effects:

    • Fast shutter speeds (i.e 1/1000th of a sec) will → let LESS light and can do freeze motion

    • Slow shutter speeds (i.e ½ of a second) → lets MORE light but can cause risk to motion blur.

  • Recommended shutter speed is 1/60 in order to mitigate blur caused by handheld camera images.

Mitigating Camera Movement

Types of Movement:

  • Addressed are

  • 1) Photographer’s body movement

- Camera not being held properly → Solution : use tripod

- Eliminating Blur from hand hold → Solution: use shutter speed closest to the focal length of lens on camera but inverted to a fraction.

  • 2) Subject motion

- A faster shutter speed will allow faster motion to be “frozen”. (Ex. 1/125 for walking whereas 1/2000 for freezing airplane propellers in motion)

-Exception for slow shutter speed is when eliminating blur from weather such as rain or snow

^So while its beneficial to document the weather conditions from a scene, images without the obscurity or blur from weather are needed.

  • 3) Camera movement :

Camera Maintenance

  • Best Practices:

    • Use of straps and lens care

    • Protect from harsh elements

    • Proper storage/carrying case

    • Store in well ventilated, cool, dry environment

  • Ensure Camera is Off:

    • Turn camera off BEFORE : changing memory, batteries, or lenses.

    • Do NOT turn camera off before : images finish downloading.

Image Quality Settings

  • Resolution Parameters:

Case Study: TWA Flight 800 Accident

  • Event Summary:

    • Overview of the TWA Flight 800 incident on July 17, 1996, detailing flight circumstances and the reconstruction of the crash scenario.

Image Quality Analysis

  • Comparative Quality Assessment:

    • Discusses high-resolution vs low-resolution image qualities in forensic applications.