Topics by Chapter
Photographic Exposure Calculations and Camera Operation
by Michael G. Prais, Ph.D.
Preface
Introduction and Motivation
What is My Midtone?
Questions to be Answered
Calculating Shutter Speed and Aperture Settings
The Exposure Equation
Representative Scenic Exposure
Targeted Photosensitive Exposure
Emulsion and Solid-state Photosensitive Arrays
Photosensitivity (Film Speed)
Midtone and Exposure Meters
Exposure Compensation
Understanding the Mathematics
Making Consistent Exposures
Exposure and the Range of Exposures
Exposure and the Quantity of Light
Scenic Exposure, Illuminance and Exposure Time
Photosensitive Response and Non-reciprocity
Sets of Exposures, Illuminances and Luminances
Matching Representative Scenic and Targeted Photosensitive Exposures
Calculating with Full and Fractional Stops
Range of Scenic Exposures
Equally Spaced Multiples of Exposure
Exposure Stops
Fractional Stops
Binary and Decimal Logarithms
Scenic Exposure Range
Photosensitive Exposure Range
The Exposure Axis
Stops on a Walk along Exposure Street
Illuminance and Luminance
Illuminances and Reflectances
Luminance as Luminous Intensity
Luminance of Reflective Surfaces in Ambient Illuminance
The Reflection Equation
The Illumination Equation
Luminance of a Reflecting Surface and Its Illuminance at a Sensing Surface
Scenic Exposure and Camera Operation
Scenic Exposure and Luminance of a Reflecting Surface
Measured Quantity of Light
Corrections that Reduce the Measured Quantity of Light
Exposure Corrections for Short Distances (Bellows Correction)
Exposure Corrections from Three-dimensional Exposure Metering
Quantities and Units
Illuminance, Exposure and Luminance
Conversions
Aperture Number and Diameter of the Aperture
Relative Shutter Speed and Exposure Time
Representative and Exact Multiple-of-Two Shutter Speeds
Photosensitive Arrays and Standard Photosensitive Characteristics
Emulsion and Solid-state Photosensitive Arrays
Optical Densities and Output Voltages
Dynamic Range nd Other Comparisons
Solid-state (SPD, CCD and CMOS) Photosensitive Arrays
Photosensitive Exposure Range
Photosensitivity, Speed Point Exposure and Reference Exposure
Midtone Exposure, Midtone Shift and the Exposure Meter Constant
Midtone Shift and Midtone Reflectance
Standard Photosensitive Exposure Ranges and Other Standard Characteristics
Emulsion Speed Points and Standard Photosensitive Exposure Ranges
Color Positive, Color Negative and Monochrome Negative Emulsions
Solid-state Speed Points and Standard Photosensitive Exposure Ranges
Spatial Resolution
Modulation Transfer Function and Spatial Response Function
Limiting (Nyquist) Spatial Frequencies for Solid-state Arrays
Spatial Resolution and Depth of Field
Tonal Resolution and Dynamic Range
ISO Equivalents for Solid-state Photosensitive Arrays
Opto-Electronic Conversion Functions (OECFs)
Photosensitive Exposure Latitude and Film Canister (DX) Coding
Exposure Compensation and Exposure in the Photosensitive Exposure Range
Problems Accepting the Manufacture’s Photosensitivity
Determining the Extent of Your Photosensitive Exposure Range
Matching the Scenic Exposure Range to the Photosensitive Exposure Range
Representative Scenic Exposures
Target Photosensitive Exposures
Exposure Value
Walking Along Exposure Street
Exposure Stop Equation
Simplified Exposure Stop Equation
Midtone Photosensitivity
Quantity of Light from Midtone Objects
Exposure Calculations
An Object in the Shade under a Clear Sky Placed at Midtone
Remembering Stop Values for Aperture Number and Relative Shutter Speed
The Moon Placed Two Stops above Midtone
Neon Lights Placed Three Stops above Midtone
Objects in Street Light Placed at Midtone
Street Lights Placed Three Stops above Midtone
Objects in Street Light Placed Three Stops below Midtone
Lights at Midtone
Objects Found Five Stops below the Metered Lights
Relative Shutter Speed, Film Speed, and the Sunny f /16 Rule
Relative Shutter Speed and the Root Speed Aperture Rule
Maximum Terrestrial Solar Luminance
Calculating the Response Range of Your Camera
Understanding and Misunderstanding Exposure Metering
Determination of Camera Setting:
Guessing and Measuring the Quantity of Light from Scenes
Comparison of Incident, Center-Weighted, Spot and Segmented Meters
All Meters Measure Illuminance
Meters are Combined Measuring and Calculating Devices
Illumination Equation and Reflection Equation
Representative Luminance Values
The Myth of 18% as Midtone
Reflective and Incident Exposure Meter Constants
Photosensitive Exposure Range and its Midtone Reflectance
Standard Characteristics of Photosensitive Arrays
Exposure Meters have never been calibrated with an 18% reflectance card
Modern Incident Meters assume a 3% gray Midtone Target to calculate camera settings
Reflective meters assume nothing about the Midtone Target
Solving the 18% Problems: Scene-dependent Quantities
Ansel Adams’ K-factor Problem
Preferred Photosensitivities:
Shifting the Midtone Exposure with Photosensitivity and Exposure Compensation
The Exposure Process
How Do I Select Midtone ?
Exposing for Highlights or Exposing For Shadows
Your Photosensitive Exposure Range and Your Target Exposure
Selecting Photosensitivity and Photosensitive Exposure Range
Recognizing the Colors and Tones in Your Photosensitive Exposure Range
Photosensitive Exposure Targets and Exposure Compensation
Precision in Choosing Exposure Values
Using Exposure Compensation and the Manufacturer’s Photosensitivity
Bracketing to Automate Recognizing Colors and Tones
Your Scenic Exposure Range and Your Representative Exposure
Representative Luminances for Scenic Exposure Range
Recognizing Reflectances as well as Luminances
Camera Calculation Modes
Matching Representative Scenic Exposure to Target Photosensitive Exposure
The Midtone Target Allows Cameras to Use Any Photosensitive Array
The Whole Process
Interest
Intention
Selection: Light, Tone, Texture, Color and Graphic Regularity
Composition: Obscurity, Eye Movement, Relative Size, Angle of View,
Field of Focus, Atmospheric Obscurity, Lines, Perspective,
View Camera Movements
Exposure: Distance to the Subject, Focal Length, Aperture Number,
Photosensitivity, Exposure Compensation and Relative Shutter Speed
Presentation
The Zone System
Creating Consistent Images by Controlling Variation in Processes
Recognizing Colors and Tones in the Scene and Image
Zones as a Function of Aperture Number and Relative Shutter Speed
Consistency allows Visualization
Keeping Records to Stabilize Your Processes
Maximizing the Extent of the Photosensitive Exposure Range
Shifting the Manufacturer’s Photosensitivity
Stability and Precision of Camera Controls
Establishing Consistency in Service Development
Comparison with the Zone System
Visualizing the Reduction of the Scenic Exposure Range
Mapping and Visualizing the Photosensitive Exposure Range
Using Exposure Compensation
Determining the Extent of the Photosensitive Exposure Range
Shifting the Manufacturer’s Photosensitivity
Visualizing the Midtone and other Targets
Placing the Scenic Exposure Range
Exposure Meters Point to the Midtone Target of the Photosensitive Exposure Range
The Exposure Stop Equation explains the Zone System
and suggests knowing the Photosensitive Exposure Range
in addition to knowing how to reduce Illuminance
Rewind and Review
The Exposure Stop Equation
Exposure Value
Determining the Quantity of Light
Exposure Meters Measure Illumination and Calculate Camera Settings
Representative Quantities of Light from the Scene
Exposure Compensation
Photosensitivity and Midtone Photosensitivity
Understanding Ansel Adams’ Exposure Calculations
Know your Photosensitive Exposure Range
Spot meter, Compensate, Record, Examine, Analyze, and Map
Appendix A: Safety Factors
Three Ways that Photographers Misunderstand Safety Factors
The Way that Jones and Condit Understood Safety Factors
Safety Factors Are No Longer Appropriate
in the Time of Modern Exposure Meters
Appendix B: Problems with Standards Documentation
Exposure Meters and Scene-dependent Quantities
Recognizing the Correct Quantities and Units
ISO Speed Ratings for “Digital” Cameras
Giving Solid-state Arrays the Same Photosensitivities as Color Positive Arrays
Ignoring the Role of Modern Exposure Meters
Ignoring the Role of the Reference Exposure Ho
The Reference Exposure Ho for Solid-sate Arrays is not determined
from the Extent of the Standard Photosensitive Exposure Range
The Location of the Speed Point for Solid-State Arrays Is Several Stops
Above the Bottom of the Photosensitive Range
and Does Not Match the Locations of the Speed Points for Any Emulsions
Lack of Information about the Extent of ISO Equivalent Ranges
Opto-electronic Conversion Functions (OECFs)
The Extent of the OECF Photosensitive Expsoure Range Does Not Match
the Standard Range for Solid-state Arrays
Introducing Errors into the OECF determination Using Perceptually Uniform Luminances
Lack of OECF Information about ISO Equivalents
The Inappropriate Effective Aperture Number
Appendix C: The Relation to and Criticism of the APEX Equation
The Additive Photographic EXposure (APEX) Equation
Problems with Scientific Units
Problems with the “N-factor”
Problems with the ISO Logarithmic Speed
Appendix D: Derivation of the Illumination Equation
Reduction of Light off the Perpendicular to the Surface
Reduction of Light by Solid Angle
Reduction of Light off the Perpendicular to the Lens
Surface Area, Image Area and Lens Area
The Unwarranted and Unnecessary Effective Aperture Number
Appendix E: Linear Perspective
Zero-Point Perspective
One-Point Perspective
Two-Point Perspective
Three-Point Perspective
Relative Movements of the Lens and the Photosensitive Array
The Scheimpflug Principle
Appendix F: Field of View
Angle of View and Focal Length
Field of View Cutout
Appendix G: Recording Information about Image Creation
EXIF and TIFF Fields
Appendix H: Derivation of Depth of Field without Approximation
Near and Far Extents of the Field of Focus
Depth of the Field of Focus
Errors and Approximations
Diameter (of the Circle) of Confusion
Lens Makers Equation and Geometric Optics
Field of Focus Equations
The Inappropriate Effective Aperture Number
Hyperfocal Distance
Appendix I: Field of Focus Tables
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