Photography lecture recording on 29 January 2025 at 14.25.49 PM

Understanding Proper Exposure in Photography

Key Concepts

• Objective of Photography: Capture color accurately and ensure subjects are well composed.

• Exposure: Refers to the amount of light that reaches the camera sensor.

  • Underexposed: Capturing less light than needed, resulting in dark, unclear images.

  • Overexposed: Capturing more light than needed, leading to bright areas losing detail.

  • Proper Exposure: Ideal balance where all subject details are captured clearly.

Exposure Variations

• Variable Adjustments: Different photographic conditions require adjusting exposure.

  • In forensic photography, initial dark images can later be adjusted to proper exposure for details.

Introduction to Stops

• Stops: The unit of measurement for exposure adjustments.

  • Adding a Stop: Doubles the amount of light.

  • Subtracting a Stop: Halves the amount of light.

• Use adjustments to maintain recognized exposure levels based on changes in light.

The Exposure Triangle

Three Key Variables

• F-Stop (Aperture): Controls the diameter of the lens opening.

  • A wider aperture (lower f-stop number) allows more light in but can reduce depth of field.

• Shutter Speed: Determines how long the camera sensor is exposed to light.

  • Faster shutter speeds allow less light but freeze motion.

• ISO: Measures the sensitivity of the camera sensor to light.

  • Higher ISO increases brightness but can introduce noise.

True and Pseudo Exposure Variables

• True Variables: F-stop and shutter speed, as they change the actual amount of light captured.

• Pseudo Variable: ISO, which affects brightness through electronic amplification rather than altering true exposure.

Adjusting for Different Lighting Conditions

• If lighting in an environment changes, adjustments must be made to f-stop, shutter speed, or ISO to achieve consistent exposure.

• Always compensate for one variable change with adjustments in others to maintain exposure balance.

Reciprocity in Exposure Variables

• Reciprocal Exposure: Adjusting two different variables to achieve the same exposure effect.

  • Example: Increasing f-stop by one stop requires a corresponding decrease in shutter speed by one stop for balanced exposure.

Camera Mechanics Explained

Digital Single-Lens Reflex (DSLR) Basics

• Viewfinder: Reflects the image through a mirror and prism; displays what the lens sees.

• Shutter Mechanism: Opens and closes to allow light to hit the sensor during exposure.

• Live View Mode: Light continuously hits the sensor for real-time viewing; involves mirror movement.

Types of Shutter Mechanisms

• Understand the difference between mechanical shutters (two curtains) and electronic shutters, but focus primarily on the mechanical aspect for this course.

• The duration of the shutter opening affects how much light is captured.

Understanding Depth of Field

• Depth of Field: Range of distance within a photo that appears sharp.

  • Wide Depth of Field: More of the image is in focus; achieved with higher f-stop numbers.

  • Shallow Depth of Field: Isolates the subject from the background; achieved with lower f-stop numbers.

Cardinal Rules for Effective Photography

1. Fill the Frame: Eliminate unnecessary background; focus on the subject.

2. Maximize Depth of Field: Use appropriate f-stop settings to control background blur.

3. Keep Digital Sensor Parallel: Ensure the camera's sensor remains parallel to the subject plane for accurate focus.

Documentation Techniques in Forensics

• Capture overall, mid-range, and close-up photographs for evidence documentation.

• As Found Photo: Capture evidence in its original condition without adjustments.

• Labeled Photos: Include scales and markers to provide context and size.

• Road Mapping: Labeling and relating evidence in context to specific locations or physical markers.

Summary of Exposure Charts and Relationships

• f-stops: Moving towards higher f-stop numbers reduces light but increases depth of field.

• Shutter Speed: Shorter exposure times reduce light captured.

• ISO Levels: Raising ISO increases brightness but can add noise; balance with f-stop and shutter speed adjustments.

Final Notes

• Understand that different photographic settings require keen adjustment and compensation for optimal results.

• Be aware of how each setting interacts in real-time and influences the resultant image in forensic photography.