Applied Photography

APPLIED PHOTOGRAPHY

O

THE FOCAL LIBRARY: EDITORIAL BOARD BERG

Prof. Dr. W. F. General Editor and Chairman of the Editorial Board, Director, Photographisches Institut der E.T.H.

Zurich, Switzerland

Professor Emeritus, Eidgenossische

K. V. CHIBISOV, Corresponding Member of the

Technische-Hochschule,

Academy

Zurich, Switzerland

Committee of Scientific Photography and Cinematography Department of

Prof. Dr.-ing h.c.

Dr.

J.

EGGERT,

Prof. Dr.

SUZANNE BERTUCAT,

Editor,

'

of Sciences of the U.S.S.R.

Chemistry,

Moscow, U.S.S.R.

Science et Industries

Photographiques ',

FRIDKIN

Paris, France

HAUTOT,

Prof. Dr. A. Director, Physical Laboratories, University of Liege, Liege, Belgium Prof. Dr.

G.

SEMERANO,

FRIESER,

Prof. Dr. H. Director, Institute for Scientific

Photography, Technische-Hochschule, Munich, Germany

HAASE, angewandte

Physik der Johann Wolfgang GoetheUniversity,

Frankfurt-am-Main, Germany Prof. Dr.

Moscow, U.S.S.R. Dr. T.

H.

JAMES,

Editor, 'Photographic Science and Engineering', Research Laboratory,

Professor of Physical Chemistry, University of Bologna, Bologna, Italy

Prof. Dr. G. Director, Institut fur

Prof. V. M. Institute of Crystallography, Academy of Science,

EBERHARD KLEIN

Director of Research, Agfa-Gevaert A.G., Leverkusen-Bayerwerk, Germany

Eastman Kodak Company, Rochester, N.Y., U.S.A.

MUELLER,

Dr. F.W. Formerly Director of Research and Development, GAF Corporation New York, U.S.A.

E. W. H. SELWYN, B.Sc, Chief Physicist and Head of Library and Information Department, Barrow, England Dr. D. A. SPENCER, Formerly Managing Director of Kodak Ltd. and Past President of the Royal Photographic Society, Rickmansworth, England Prof. Dr.

M. T AMUR A,

W. D. WRIGHT,

Department of Industrial Chemistry,

Professor of Applied Optics, Imperial College of Science and Technology,

Faculty of Engineering, University of

London, England

Prof. Dr.

Kyoto, Kyoto, Japan

Publishers

FOCAL PRESS LIMITED 31 Fitzroy Square, London, W.l, England

APPLIED PHOTOGRAPHY

C.R.Arnold

P. J. Rolls

J.C.J. Stewart

Edited by

D. A. Spencer

THE FOCAL PRESS LONDON and NEW YORK

1971

FOCAL PRESS LIMITED

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system,

or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the copyright

owner

First Edition 1971

ISBN

Printed

in

240 50723

1

Great Britain at The Curwen Press, Plaistow, London E.13.

CONTENTS

INTRODUCTION BY

D. A.

SPENCER

1.

21

SENSITOMETRY

1.1

Introduction

23

1.2

Exposure

23 23 24 26 28 28 28 28 29 29 30

1.2.1

Storage before exposure

1.2.2

Latent image regression Reciprocity failure ntermittency effect

1.2.3 1.2.4 1.2.5 1.2.6

1

.3

Sensitometers 1.2.6.1 Basic classification 1.2.6.2 Time-scale sensitometers 1.2.6.3 Intensity-scale sensitometers 1.2.6.4 Commercial sensitometers 1.2.6.5 Design features of sensitometers

31

Processing 1.3.1

1.3.2 1.3.3

1.4

I

Wavelength

Development 1.3.1.1

Dish processing

1.3.1.2

Tank development

1.3.1.3

Continuous processing machines

1.3.1.4 Special sensitometric processing Fixation and washing

machines

Drying

Measurement of density 1.4.1 Types of density 1.4.1.1

1.4.2

Specular density

1.4.1.2

Diffuse density

1.4.1.3

Callier coefficient

1.4.1.4 1.4.1.5

Colour coefficient Colour densitometry

1.4.1.6

Reflection density

Densitometers 1.4.2.1

1.4.2.2 1.4.2.3 1.4.2.4 1.4.2.5

Visual densitometers Direct reading photo-electric densitometers

Recording densitometers The use of densitometers Plotting results

32 32 33 34 35 35 35 3g 35 35 36 37 38 39 40 40 4-]

41

43 43 43 45

.5

1

Expression of sensitometric results Characteristic curves 1.5.1 Derivative curves 1 .5.1 .1 Contrast 1 .5.2

1.5.3 .5.4

1

1.5.5 1.5.6 .6

1

1.5.2.1

Gamma

1.5.2.2

Average gradient

1.5.2.3

Contrast Index

Gamma/time curves Temperature/time graphs Film speed Fog

Applications of sensitometry Process control 1 .6.1 1.6.2 X-ray sensitometry Spectrosensitometry 1 .6.3 1.6.4

Reprography 1.6.4.1

1

.6.5

1

.6.6

1.6.7 1

.7

1.7.2

Principles

Precautions

1.7.1.3

Image illumination

1.7.1.4

Wedge

.7.2.3

Dosimetry photometry

Stellar

2.2.2 2.2.3

Spatial resolution Time resolution Tonal discrimination 2.2.3.1

2.2.3.2 2.2.3.3

2.2.4 2.2.5 2.2.6

56 57 57

59 62 62 64 64 64 65 65 65 66 67

67

71

Digital recording

Resolution 2.2.1

54 54 54 55 55 56

INFORMATION CAPACITY AND RESOLUTION

Introduction 2.1.1

2.3

neutrality

Applications Determination of liquid film thickness 1.7.2.1 Determination of effective printing densities 1.7.2.2 1.7.2.4

2.

Calibration steps

1.7.1.2

1

51 51

61

Tone reproduction

1.7.1.1

2.2

densitometry

Photographic photometry 1.7.1

2.1

UV

Integrated half-tone dot densities 1.6.4.2 Filter factors Application of gamma/time curves and speed/time curves

45 45 46 47 47 48 49 49

Exposure scale Increase of exposure scale Available exposure levels

2.2.3.4 Signal to noise ratio Extended Range film 2.2.3.5 Colour discrimination

Total information capacity Informational sensitivity

The photographic system

71

72 72 73 73 73 74 75 76 77 78 78

80 80

4 3

2.4

Spatial resolution of lenses 2.4.1 Abbe formula

2.4.2

2.5

82 82 82 82 83 85 85 87 89 89 90 90

Diffraction limited lenses 2.4.2.1 Practical considerations

2.4.3 Subject resolution and image resolution Spatial resolving power of emulsions 2.5.1

2.5.2

Graininess Granularity

2.5.2.1 Wiener granularity spectrum Turbidity Spread function and Acutance 2.6.1 Emulsion spread function 2.6.2 Lens spread function Resolution testing

2.5.3

2.6

2.7

2.8

2.7.1

Practical considerations

2.7.2 2.7.3 2.7.4

Exposure and processing factors Film and lens combination Limitations of resolution testing

Modulation Transfer Function 2.8.1

Basic

MTF

theory

Adjacency effects MTF cascade properties Variation of MTF with exposure Phase 2.8.1.1

2.8.2 2.8.3 2.8.4

2.9

2.8.5 Single-figure expression of MTF values 2.8.6 Interpretation of MTF curves Inter-related properties of emulsions

3.

3.1

3.3

92 93 95 96 96 97 97 99 100 1 00 101

102 104 105

LIGHT SOURCES

Properties of electromagnetic radiation 3.1.1 The dual nature of light 3.1.2 Wavelength 3.1.3 Quantum energy 3.1.4 Coherence 3.1.5 Generation of EM R

109 109 1 Qg 109 11q

Incandescence (thermal radiation) 3.1.5.2 Luminescence The electromagnetic spectrum

110

3.1.5.1

3.2

level

91

3.2.1

Cosmic

3.2.2 3.2.3 3.2.4 3.2.5 3.2.6

Gamma

rays

rays Ultraviolet Light

3.3.2 3.3.3 3.3.4

Infrared

Luminous Luminous

1 1

113 113 11

intensity

flux

Illuminance

Luminance 3.3.4.1

H2 H2 112

and X-rays

Radio waves Photometry 3.3.1

HO

Reflection factor

H4 ... H5 H7 H7 Hg H9

3.3.5

3.3.6 3.3.7 3.3.8 3.3.9

3.4

3.5

Factors affecting subject illumination Inverse square law 3.3.5.1 Cosine law 3.3.5.2 Cos 3 6 law 3.3.5.3 Calculation of the evenness of illumination Exposure calculation from illuminance data

Guide numbers Guide numbers 3.3.8.1

for tungsten

lamps

Power requirements

Spectral quality Spectral energy distribution curves 3.4.1 3.4.2 Colour temperature Efficiency of light sources Luminous efficiency 3.5.1 3.5.2 Actinic efficiency 3.5.3 3.5.4 3.5.5

Optical efficiency Reflector efficiency

3.6

Source size Duration and lamp life

3.7

Duration of flash sources Life of continuous sources 3.6.2 Lamp flicker 3.6.3 Types of light source 3.6.1

3.7.1

Tungsten lamps Performance 3.7.1.1 Spectral emission

3.7.1.2 3.7.1.3

Integral reflectors

3.7.2

Flashbulbs

3.7.3 3.7.4 3.7.5

Carbon arcs

3.7.6

3.7.7 3.7.8

Spectral quality and luminous efficiency 3.7.6.2 Electronic flash Lasers Principles 3.7.8.1 3.7.8.3

Q-switched lasers Spectral bandwidth

3.7.8.4

Optical properties

Applications of lasers Electro-luminescent diodes (optical semi-conductors) 3.7.9 Economic factors in the choice of lighting equipment 3.7.8.5

3.8

4.

4.1

121

122 123 123 123 124 124 125 125 1 25 126 1 26 12 6 12 Z I 2? 12/ 127

128 128 129 129 129 131 131

32 132 132 I

Pyrotechnic sources Discharge lamps Designation of mercury discharge lamps 3.7.5.1 Spectral emission 3.7.5.2 Fluorescent lamps Construction 3.7.6.1

3.7.8.2

119 119 119 119

133 133 134 135 135 135 137 1ci/

139 139 139 141 141 141

MACROPHOTOGRAPHY

Forming a macro image Cameras for macrophotography 4.1.1 Relation between extension, focal length and magnification 4.1.2 Importance of swing movements 4.1.3

>"*£

146 146 1

46

Lenses for macrophotography 4.1.4.1 Choice of focal length

4.1.4

Resolution, aperture and depth of field

4.1 .4.2

4.2

Illumination

Bright field reflected (or vertical incident) illumination Dark field illumination Transmitted illumination Illumination for modelling

4.2.1

4.2.2 4.2.3 4.2.4 4.2.5

4.3

4.4

Ring illuminators

Exposure 4.3.1

Effect of magnification

4.3.2

Exposure determination

Practical operation 4.4.1

Backgrounds

4.4.2 4.4.3 4.4.4 4.4.5 4.4.6 4.4.7

Holding the subject Focusing screens Focusing the image Magnification markers Filters

Negative materials

5.

5.1

5.2

5.1.3 5.1.4 5.1.5 Optical 5.2.1

Useful magnification field

components Objectives 5.2.1.1

5.2.1.2 5.2.1.3 5.2.1.4 5.2.1.5 5.2.1.6

Primary magnification (nominal) Numerical aperture

Working medium Cover glass thickness Mechanical tube length Degree of correction

Special objectives 5.2.2.1 Reflecting objectives 5.2.2.2 Objectives for reflected incident light

5.2.3

Eyepieces 5.2.3.2 5.2.3.3 5.2.3.4 5.2.3.5

5.2.4

Ramsden eyepiece Compensating eyepiece Flat field and wide field eyepieces Projection or photographic eyepieces and amplifying projection lenses

Substage condensers Bright field condensers

5.2.4.2

Dark field condensers Condensers for reflected

5.2.4.3

5.2.5

Huygenian eyepiece

5.2.4.1

Bertrand lens

163 164 164 166 167 169 169 169 169 169 170 171 171

5.2.2

5.2.3.1

153 153 155 155 156 157 157 157 157 157 159 15g 159

161

Numerical aperture Resolution of the objective

Depth of

151 151 151

PHOTOMICROGRAPHY

Microscope image formation 5.1.1 Forming a real image 5.1.2

147 147 1 49 150

light

174 174 174 176 176 176 176 177 177 178 178 179 179 179

5.3

Microscope illumination 5.3.1

5.3.2 5.3.3

5.4

Dark field transmitted light 5.3.4 Reflected illumination— bright field or vertical incident 5.3.5 Dark field reflected illumination 5.3.6 Special techniques 5.4.1 Polarised light 5.4.2 Phase contrast Equipment for phase contrast 5.4.2.1 Phase contrast with reflected light 5.4.2.2 5.4.3

5.4.4 5.4.5

5.5

Light sources Illumination technique Bright field transmitted illumination Kohler illumination 5.3.3.1 Critical illumination 5.3.3.2

Interference microscopy 5.4.3.1

Double beam interferometry

5.4.3.2

Multiple

interferometry

UV

Photographic recording 5.5.1

Camera equipment

5.5.2 5.5.3 5.5.4 5.5.5

Photomicroscopes Cinephotomicrography Colour filters Sensitive materials

5.6

Specimen preparation Specimens for transmitted light 5.6.1 Mounting media 5.6.1.1 5.6.2 Specimens for reflected light

5.7

Electron micrography 5.7.1

Transmission microscope Photographic materials for electron microscopy 5.7.1.1 Cine-electron micrography 5.7.1.2

5.7.2

Scanning electron microscope

6.1

184 184 184 186 186 186 189 191

192 192 192 194 1 95 196 196 196

1" 199 200 202 202 203 203 204 205 205 206 208 209

Illumination of the original

213 213 214 217 217 218 218 219 219

Exposure technique

221

Processing Applications

223 224 224 224 224 224 225

Extreme resolution microphotography 6.1.1

Optical considerations

6.1.2

Sensitive material

6.1.1.1

6.1.2.1

6.1.3 6.1.4 6.1.5 6.1.6 6.1.7

181 181 181

MICROPHOTOGRAPHY

6.

Focusing

Concentrated Lippmann emulsions

6.1.2.2

Photoresists

6.1.2.3

Other sensitive materials

The

original

6.1.7.1 6.1 .7.2

6.1.7.3

6.1.7.4 6.1.7.5

10

beam

photomicrography Fluorescence photomicrography

Ultraviolet

180 180

Graticules Coded scales and gratings Production of small components Microelectronic devices Image evaluation

6.2

Document microcopying 6.2.1 The documents Photographic factors

6.2.2 6.2.3

Microfilm cameras 6.2.3.1 Flat-bed cameras 6.2.3.2 6.2.3.3

Unitized Systems Non-silver processes

6.2.4 6.2.5

7.

7.1

Introduction

7.2 7.3

Infrared sources in

the infrared

7.3.1.1

Absorption

7.3.1 .2

Scattering

Lenses 7.3.2.1

Conventional lenses

7.3.2.2 7.3.2.3

Special IR optical materials Resolution

7.3.3 Filters 7.3.4 Camera materials Infrared emulsions 7.4.1

Ektachrome Infrared

7.4.2

Herschel effect

film

Detectors 7.5.1

Classification 7.5.1.1

7.5.1.2

7.5.2

7.6

231 231

Atmosphere

7.3.2

7.5

INFRARED PHOTOGRAPHY

Optical properties of materials 7.3.1

7.4

Flow cameras Step and repeat cameras

Thermal detectors Photon detectors

Photo-electric cells 7.5.2.1 Photo-voltaic cells 7.5.2.2 Photo-emissive cells 7.5.2.3 Photo-conductive cells

Infrared imaging systems 7.6.1

Image convenor tubes

7.6.2

Infrared vidicon

7.6.3

Thermographic scanning systems 7.6.3.1 Real-time thermography 7.6.3.2 Colour thermography Evaporography Phosphorography

7.6.4 7.6.5

7.6.5.1

7.6.6 7.6.7

Extinction of fluorescence 7.6.5.2 Stimulation of visible luminescence by infrared Liquid crystals

Expansion of photographic gelatin layer Frequency summing Applications of infrared photography 7.7.1 Nocturnal photography 7.6.8

7.7

7.7.2 7.7.3

225 226 226 227 227 227 228 228 229

Industrial applications

Photographic thermometry

232 232 232 232 233 233 235 235 235 237 238 240 240 240 240 240 241 241 241

242 243 243 243 244 244 245 246 246 247 247 249 250 250 250 250 251 251 251 11

7.7.4

Aerial

photography

7.7.4.1

Forestry

7.7.4.2

Camouflage detection Geological survey

7.7.4.3

7.7.5 7.7.6 7.7.7 7.7.8

Biology

Astronomy and spectroscopy Forensic work Medicine

ULTRAVIOLET PHOTOGRAPHY

8.

8.1

Introduction 8.1.1

8.2

8.3 8.4

8.2.3 Electronic flash 8.2.4 UV-emitting fluorescent tubes 8.2.5 Commercial UV lamp units 8.2.6 Lighting technique Optical materials Filters

8.4.2 8.4.3

8.5

Terminology

Sources of ultraviolet radiation 8.2.1 Incandescent sources 8.2.2 Gas discharge lamps

8.4.1

UV transmitting filters UV absorbing (barrier)

filters

Accessory filters Ultraviolet optical systems 8.5.1 Lenses Pinholes and Zone plates 8.5.2 8.5.2.1

Pinholes

8.5.2.2

Zone

8.6

UV

8.7

Emulsions for

plates

detectors

8.6.1

UV image converters UV photography

8.7.1

Spectral sensitivity

8.7.2

Gamma-lambda

effect

Gelatin absorption Fluorescent emulsion coatings 8.7.4 Non-silver photo-sensitive materials 8.7.5 Medical and biological effects of UV radiation 8.7.3

8.8 8.9

Practical requirements in

UV

photography

UV

recording Recording fluorescence

8.9.1

Direct

8.9.2 8.9.3

Exposure settings

UV

photography

8.9.3.1

Direct

8.9.3.2

Fluorescence recording

8.10 Applications of UV photography Medicine 8.10.1 8.10.2 8.10.3 8.10.4 8.10.5 8.10.6

12

UV chromatography Industrial applications

UV

252 252 253 253 253 253 253 254

astronomy

Forensic work Nocturnal photography

257 257 257 257 258 258 258 261

263 264 265 265 266 267 268 268 269 269 269 270 270 272 272 273 274 274 274 275 276 276 277 279 279 279 280 280 280 280 281 281 281

9.

RADIOGRAPHY

9.1

Introduction

9.2

Radiographic sources 9.2.1 X-ray sources 9.2.2 Gamma ray sources 9.2.2.1 Energy 9.2.2.2

9.2.3

9.3

Activity 9.2.2.3 Half-life Electron shadowgraphs

Radiographic materials 9.3.1

Sensitised materials 9.3.1.1

9.3.1.2

9.3.2

X-ray films Xero-radiography

9.3.1.3 Solid state detectors Intensifying screens

Salt screens 9.3.2.2 Metal screens Basic factors in radiographic technique 9.3.2.1

9.4

9.4.1

Exposure

9.4.2 9.4.3 9.4.4

Processing Radiographic sensitivity Radiographic sharpness 9.4.4.1 Geometrical factors 9.4.4.2 Scattered radiation 9.4.4.3 Subject movement 9.4.4.4 Salt-screen unsharpness 9.4.4.5 Film sharpness

Film speed Exposure scale 9.4.7 Reproduction of radiographs Fluoroscopy 9.5.1 Fluorography 9.5.2 X-ray image tubes Gamma radiography 1 9.6.1 Neutron radiography Special radiographic techniques 9.7.1 Micro-radiography 9.7.1.1 Contact micro-radiography 9.7.1.2 Projection micro-radiography 9.7.1.3 Reflection X-ray microscopy 9.7.1.4 X-ray scanning microscopy 9.7.2 Autoradiography 9.7.3 High speed radiography 9.7.3.1 Flash radiography 9.7.3.2 Cine-radiography 9.4.5 9.4.6

9.5

9.6 9.7

10. 10.1

Principles 10.1.1

283 283 283 285 285 285 287 287 288 288 288 289 289 289 289 289 290 290 290 291

292 292 292 293 293 293 294 294 294 295 296 297 297 298 298 298 298 299 299 300 300 301 301

302

CINEMATOGRAPHY

and methods Camera and equipment 10.1.1.1

Intermittent

10.1.1.2

Shutters

mechanism

305 305 305 306 13

306 306 307 307 310 310 310 310

Viewing and focusing Motors and magazines Film type and size 1 0.1 .1 .5 Applied cinematography Time lapse cinematography Filming and television 10.1.1.3 10.1.1.4

10.1.2 10.1.3 10.1.4

10.1.4.1

10.1.4.2

10.2

10.2.2 10.2.3

Manual methods Machine processing Cine film printing 10.2.3.1 Contact printers 10.2.3.2 10.2.3.3 10.2.3.4

10.5

11.2

Equipment

HIGH SPEED PHOTOGRAPHY

11.2.1.6 Stroboscopes Continuous illumination 11.2.2.1

Methods

11.2.2.2

Light sources

11.3.2

Electro-optical shutters Capping shutters

High speed cameras Framing and streak cameras 11.4.1 11.4.2 Intermittent motion cameras 11.4.3 Continuous film movement cameras Rotating prism cameras 11.4.3.1 11.4.3.2 11.4.3.3 11.4.3.4

14

Features of Fastax and Event synchronisation

Time bases

323 323 323 324 324 324 326 327 328 329 329 331 331 331

Shutters 11.3.1

11.4

312 313 313 314 314 processing houses 314 315 315 315 317 317 317 318 318 318 319

Introduction Exposure duration and spatial resolution 11.1.1 11.1.2 Time resolution Illumination Short duration flash 11.2.1 11.2.1.1 Electronic flash 11.2.1.2 Spark gaps Multiple spark systems 11.2.1.3 Pyrotechnic light sources 11.2.1.4 Electron stimulated sources 11.2.1.5

11.2.2

11.3

printing

Services provided by motion picture

10.3.2 Editing procedures Projection Projectors 10.4.1 10.4.2 Projection conditions 10.4.3 Sound film projection Sound recording Magnetic recording 10.5.1 10.5.2 Optical recording

11. 11.1

Projection or optical printers

Sound

Editing 10.3.1

10.4

311 311

Processing 10.2.1

10.3

Films for television transmission Filming television images

Hycam cameras

332 332 334 334 334 335 335 335 337 342 342

11.4.3.5 11.4.3.6

11.5

11.4.4 Drum cameras 11.4.5 Rotating mirror cameras 11.4.6 Image tube cameras 11.4.7 Image dissection cameras Data analysis 11.5.1 Analysis projectors 11.5.2 Film analysers

12. 12.1

12.2

Equipment

12.2.2 High 'G' cameras 12.2.3 Instrument panel recording Special instruments and techniques 12.3.1 Cinetheodolites 12.3.2 Tracking telescopes 12.3.3 Fairchild flight analyser 12.3.4 Race finish recording

13. 13.1

13.2

13.3

13.4

343 343 344 345 347 348 349 350 350

INSTRUMENTATION AND RECORDING

Oscillograph recording 12.1.1 C.R.O. Methods 12.1.2 Phosphor characteristics 12.1.3 Writing speed (photographic) 12.1.4 Single shot recording 12.1.5 Continuous feed recording 12.1.6 Sensitive materials 12.1.7 Recording in colour 12.1.8 Radar scope recording 12.1.9 Direct recording oscillographs General recording 12.2.1

12.3

Other compensating systems Cameras with rapid acceleration

353 353 353 354 355 357 358 359 360 360 361 361

362 362 363 353 364 364 355

STEREOSCOPIC PHOTOGRAPHY

Definition of terms Visual factors 13.2.1 Monocular vision 13.2.2 Interpretation 13.2.3 Binocular vision 1

3.2.3.1

1

3.2.3.2

367 367 367 368 368

Calculation of the minimum perceptible subject-plane separation Calculation of the farthest point of binocular

369

vision

37

13.2.4 Stereoscopic vision Stereoscopic reconstruction 13.3.1 Hyperstereoscopy 13.3.2 Hypostereoscopy Camera techniques 13.4.1 Stereographic cameras 13.4.2 Stereographic attachments 13.4.2.1

Two-mirror beam

370 371

splitters

372 373 374 374 374 374 15

Four-mirror beam splitter Interchangeable twin stereo lenses 13.4.2.3 The use of normal cameras Twin cameras 13.4.3.1 13.4.3.2 Single-camera methods 13.4.3.3 Subject adjustment methods Defects in perspective 13.4.2.2

13.4.3

13.5

13.6

13.4.4 Stereoscopic viewing methods 13.5.1 Simple systems 13.5.2 Mirror systems 13.5.3 Lens viewers 13.5.4 Anaglyphs Polychromatic anaglyphs 13.5.4.1 13.5.5 Polarised light systems 13.5.6 Autostereoscopic methods Parallax stereograms 13.5.6.1 Parallax panoramagrams 13.5.6.2 Applications of stereophotography 13.6.1

Stereomicrography Conventional microscopes 13.6.1.1 13.6.1.2 Twin-objective microscopes

13.6.2 13.6.3

Stereoradiography Publication of stereographs

13.6.1.3

14.

Split-field objectives

PHOTOGRAMMETRY

14.1

Introduction

14.2

Photogrammetric principles Single camera (mono-photogrammetry) 14.2.1 14.2.2 Pairs of cameras (stereo-photogrammetry) 14.2.3 Simple depth measurement 14.2.4 Height displacement

14.3

Cameras 14.3.1

14.3.2

14.3.3 14.3.4 14.3.5 14.3.6

Basic camera features for photogrammetry Lenses for photogrammetry 14.3.2.1

Focal length

14.3.2.2

Distortion

Phototheodolites Cinetheodolites Short-base stereo cameras

cameras Photo-reconnaissance 14.3.6.2 Cartography 14.3.6.3 The influence of aircraft environment 14.3.6.4 Aircraft movement and attitude

Aerial

14.3.6.1

14.3.7

14.4

14.4.1

14.4.2

16

Film flatness 14.3.6.5 14.3.6.6 Air survey lenses Special cameras Fish-eye lenses 14.3.7.1

14.3.7.2 Stereometric plotting

375 375 376 376 376 377 377 377 377 377 378 378 378 380 382 382 382 383 383 383 383 383 383 384

Panoramic cameras

Analytical plotting Graphical plotting

387 387 387 387 389 390 392 392 393 393 393 395 397 397 398 398 399 399 399 399 400 400 400 401 401 401 4 °1

14.5

Sensitised materials 14.5.1 Stability of support materials 14.5.2 Handling of paper base materials 14.5.3 Emulsion movement

14.6

Photogrammetric applications 14.6.1

Aerial survey

14.6.2 14.6.3 14.6.4 14.6.5 14.6.6 14.6.7 14.6.8 14.6.9

Geodesy Photogrammetry from Astronomy Bubble chambers Medicine Industry Architecture

Radar

15.

PHOTOGRAPHIC VISUALISATION

15.1

Introduction

15.2

Simple flow visualisation 15.2.1 Aerodynamics

15.2.2

411 411 41

15.2.1.1

Tufts and flags

411

15.2.1.2 15.2.1.3 15.2.1.4

Smoke

412 412 412 412 412 412 413 413 413

tracers

Solid tracers

Surface coatings

Hydrology Surface tracers Sub-surface flow Droplets and sprays

15.2.2.1

15.2.2.2 15.2.2.3

Work flow and motion

15.2.3

15.2.3.1

15.3

satellites

Oscillatory

analysis

movements

Special optical systems

Shadowgraphs

15.3.1

Direct shadowgraphs 15.3.1.2 Camera-recorded shadowgraphs Schlieren systems Interferometry 15.3.3.1 Interference 15.3.3.2 Mach-Zehnder interferometer 15.3.3.3 Surface topography Moire" fringes 15.3.1.1

15.3.2 15.3.3

15.4

1

5.5

15.6

15.3.4 Polarised light techniques 15.4.1 Photoelastic stress analysis 15.4.1.1 Birefringence 15.4.1.2 The polariscope 15.4.1.3 Interpretation Tone derivation processes 15.5.1 Equidensitometry 15.5.2 Tone separation 15.5.3 Image comparison

Holograms 15.6.1

15.6.2 15.6.3 15.6.4

402 402 404 404 405 405 406 406 406 407 407 407 407 408

Recording holograms Reconstruction Characteristics of holograms Applications of holography

414 414 414 414 416 41 g

419 419 420 422 422 422 422 424 424 426 426 428 428 429 429 432 433 433 17

15.7

False-colour methods Optical systems 15.7.1 15.7.2 Colour coding of light sources 15.7.3 False-colour sensitised emulsions 15.7.4 Colour conversion printing

15.8 15.9

Microwaves Sound and ultrasound Acoustical holograms (sonoholograms) 15.9.1

15.7.5

16. 16.1

16.2

Colour radiography

APPLICATIONS OF PHOTOGRAPHY

16.4.5 16.4.6

16.6 16.7 16.8

Speed

Dimensional stability 16.4.2.1 Metal preparation Coating Dip-coating 16.4.4.1 16.4.4.2 Flow coating 16.4.4.3 Spray coating 16.4.4.4 Roller coating Pre-bake Exposure Double-sided exposure 16.4.6.1

16.4.7 16.4.8 16.4.9

Development

16.5.1

Thin film circuits

Post-bake

Etching 16.4.10 Stripping 16.4.11 Inspection 16.4.12 Screen-printed circuits 1 6.4.1 3 Xerographic method Integrated circuits 16.5.2 Semi-conductor integrated circuits Photo-lofting

Three-dimensional photo-polymer models Drawing-office applications

17. 17.1

ENGINEERING

16.2.1.2 Spectral sensitivity 16.2.1.3 Solid content 16.2.1.4 Resolution Photo-fabrication Printed circuits Drawing the art-work 16.4.1 16.4.2 Photography

16.4.3 16.4.4

16.5

IN

Introduction Photo-sensitive resists Properties of photo-resists 16.2.1 16.2.1.1

16.3 16.4

434 434 434 434 435 435 436 436 438

441

442 442 442 443 443 443 444 444 444 445 445 445 446 446 446 446 446 446 446 446 447 447 447 448 448 448 449 449 449 450 451

452 452

SPECIAL PURPOSE CAMERAS

'Convenience' Designs Basic camera system 17.1.1 17.1.2 Critical dimensions

455 455 457

17.1.3 1 1

7.2

7.1 .4

Specific purpose cameras 17.2.1 Periphery camera 17.2.2 Panoramic camera 1 1

7.2.3 7.2.4

18. 18.1

18.2

18.3

Telephotography 18.1.1 Long-focus lenses 1 8.1 .2 Photography via telescopes Endoscopic photography 18.2.1

Optical principles

18.2.2 18.2.3 1 8.2.4

Lighting

Focusing methods

methods

Uses of fibre optics Photography of radioactive materials 18.3.2 18.3.3 18.3.4

18.5

Orthographic camera using telecentric optics Bubble chamber camera

458 458 459 459 460 462 463

PHOTOGRAPHY OF INACCESSIBLE OBJECTS

18.3.1

18.4

Constructional materials Examples of specific camera design

Safety precautions Photography in glove boxes

Photography in lead cells Photography in concrete cells Remotely controlled cameras 18.4.1 Underwater photography Closed circuit television 1 8.5.1 Recording the television image

467 467 468 470 470 471

472 473 474 474 474 474 474 477 477 478 478

Appendices APPENDIX A

Wavelength

APPENDIX B

Standards Institution Publications

APPENDIX C

Photographic content of scientific journals

INDEX

units

481

483 485 487

19

INTRODUCTION The term applied photography' covers the uses of photography for the production of records of value the study, understanding and control of basic processes in all branches of science, industry and education.

m

Most of us are now surely aware that photography has other applications than entertainment or comment on the times we live in— that amateur, professional, news and motion picture photography is not the whole story. We are, however typically startled to learn that the majority of the world's output of photographic material is used in these other applications. The basic contribution of photography to science is the provision of records that cannot be made any other way. Although our knowledge of the external world and our mastery over it depends entirely on our five senses, the development of science and technology ultimately depends on making observations by eye and scientific effort is almost entirely concentrated on transforming phenomena into a form that can be seen and studied at leisure.

m

The camera provides us with a

sort of synthetic eye— a detached retina with an of turning into visible records phenomena whose existence we should otherwise neither suspect nor understand. The methods of using photography as a tool can be broadly divided into two groups 1 Making illustrations for record, demonstration or investigation purposes of thines infallible

memory—capable

which the eye can see. 2 Recording phenomena under conditions where the human eye

&

is

helpless

either

because the light is too bright, too dim or too transient to see by or because the radiation of interest does not give rise to vision. This second group has led to the development of cameras ranging in size from instruments small enough to be swallowed to others weighing several tons as well as hundreds of specialized r photographic ° r materials.

In the circumstances, it is perhaps surprising, if understandable, that the majority of textbooks on photography are written to inform and help the users of conventional cameras making pictures in the conventional sense of the word. Much of the information such texts contain is irrelevant to the newcomer to applied photography. He has, typically, only a limited number of specialised textbooks or papers scattered through journals to turn to and, in consequence, only too often his attempts to apply photographic techniques to new problems is hindered by misunderstanding of the relevant characteristics of the sensitive materials or ignorance of the facilities and techniques already available. The devising of new applications is then hindered or made unnecessarily costly.

As no one possesses personal experience in all branches of applied photography book is the product of collaboration between three experts who,

present

have covered the

th-

between them"

field in a most comprehensive manner. Besides covering the basic fundamentals which the applied photographer needs to understand, the resulting text is an authoritative survey of the amazing diversity of the uses to which photography has been turned by human ingenuity.

D. A.

SPENCER 21

ACKNOWLEDGMENTS to thank the following for their constructive comments on sections Cooper, L. E. Elliott, J. C. Rockley, P. B. Nuttall-Smith, W. J. R. G. book: of this co-operation of Sexton, Dr. D. E. W. Stone, W. McL. Thompson and W. Turner. The acknowledged. gratefully also is colleagues many other friends and The following organisations have supplied technical information and their assistance cases, and permission to publish details of their products or techniques, and in some

The authors wish

acknowledged. Acmade Ltd., A.E.I. Lamp & Lighting Co. Aga (U.K.) Ltd., Agfa-Gevaert Ltd., P. W. Allen & Co., Ltd., Aga The Amateur Photographer, American National Standards Institute, Aveley Electrics Bausch & Lomb Optical Co. Ltd., Balzers High Vacuum Ltd., Barr & Stroud Ltd., & Stanley Ltd., British LightBellingham Ltd., Howell Bell & Ltd R. & J. Beck Ltd., Ltd., Central Electricity Instruments Scientific Cambridge Ltd., 'industries ing Cossor Electronics Ltd., AG, Generating Board, Chance Brothers Ltd., Contraves Instruments Ltd., Dawe Ltd., Electronics Dale C Z. Scientific Instruments Ltd., GmbH, Direct Orwo-Film-Export und KameraDeutsche Ltd., & Co. Degenhardt

illustrations are gratefully

Standard Ltd.,

'

Duval

Ltd.,

Photographic Supplies Ltd., Dumont Oscilloscope Laboratories Inc., Ltd., Engelhard Ealing Beck Ltd., Eclair Debrie (U.K.) Ltd., E.M.I. Electronics Electroselemum Evans Ltd., Instruments) (Photographic Hanovia Lamps, Envoy Ltd., Foster Instrument Co. U.K. Emission Field Ltd., Power-Optics Evershed Ltd., Cameras Ltd., Guest Electronics Ltd., Ltd.^ Gillett & Sibert Ltd., John Godrich, Gordon Hilger & Watts Ltd., Ilford Ltd., Ltd., Instrumentation) John Hadland (Photographic Ltd., Joyce, Loebl & Co. Hendon of Johnsons Ltd., Grey) R. (D. Division Instruments Ltd., Leland (Instruments) Leitz Ltd Kodak Ltd Lee Smith Photomechanics Ltd., E. Metallographic Ltd., Company 3M Ltd., Instruments Ltd., Lunartron Electronics Micro-Instruments (Oxford) Ltd., Services Laboratories Ltd., Micro Cine Ltd., (renamed, ex-Ministry of TechIndustry and Trade of Department Co., Milliken D B Laboratory, Ministry of Physical National Hydraulics Research Station— ,

nology)—

Royal Aircraft EstablishAviation Supply (renamed, ex-Ministry of Technology)— Guardia Ltd., Newman Co. Register Cash National Inc., Morgan ment Morgan Ltd., Works Optical Ltd., Reactors Ltd 'Nuclear Enterprises (G.B.) Ltd., Optec Ltd., Brothers Pilkmgton Ltd., Electrical Philips Osram-G E C. Ltd., Pantak Ltd., Ltd., Racecourse Technical Chemicals,Polaroid(U.K.)Ltd.,TheProjectinaCo. P Audio Visual Ltd., Rank Precision Industries Ltd., Research

&

&

MD

Services Ltd.,

Rank

&

Sons Ltd., Shandon Science Research Council, David Shackman Engineers, Scientists Photographic of Society Ltd., Skan Scientific Ltd., H. V. Electrical Instruments Ltd., Turner Ernest Ltd., Electric Thorn Ltd., Products Telford Vinten Ltd., Vinten United Kingdom Atomic Energy Authority, Vickers Ltd., W.

Engineers Ltd

W. Watson & Sons Ltd., Wild Heerbrugg Ltd., Carl Zeiss, Oberkochen. Co. Manufacturing Williamson Ltd.,

Mitchell Ltd., Vision Engineering Ltd.,

(U

22

K

)

&

1.

1.1

SENSITOMETRY

Introduction

An understanding of sensitometric principles must be one of the primary aims of the applied photographer. The term sensitometry is not used here in the narrow sense of film speed determination, but covers practical comparison of materials, process control and the various forms of photographic photometry. In all these fields a methodical approach is essential if meaningful results are to be obtained. The general principles and terminology are well enough known. The intention here is to re-state briefly the basic language of the subject, to mention some of the equipment used and to discuss some of the problems that can arise in the application of sensitometric methods. Sensitometric tests do not allow evaluation of all aspects of photographic performance and picture tests may be necessary to check that the normal sensitometric

criteria

are valid for a particular application.

Absolute sensitometry implies that the total exposure (image illuminance x exposure duration) given to the film is known quantitatively (in lux-seconds). This is normally required only for absolute film speed determination (see p. 51) and in most cases comparative sensitometry is adequate, in which it is sufficient to know that the exposure is constant from test to test. The image illuminance is not, therefore, normally measured, although the duration of exposure must be specified to avoid discrepancies

due to reciprocity failure. There are four basic stages in any sensitometric experiment: Exposure and storage of the film Processing

Measurement (densitometry) Interpretation.

1.2

Exposure

1.2.1 Storage before exposure. No photographic emulsion has a constant film speed throughout its life and comparisons should only be made on materials of the same batch that have had the same storage history prior to exposure. In addition, there are always small variations within a large batch of material and for critical work a series of tests must be made to establish the mean characteristics (see p. 54). In such work great care is necessary to ensure that any observed variations are not due to inconsistent processing or other errors in handling by the photographer. Considerable changes in emulsion speed, contrast and colour balance occur immediately after manufacture, but the rate of change has greatly reduced by the time the material is released to the public. However, the speed and contrast continue to drop slowly and the fog level rises throughout the life of the film. A reduction of one-third of a stop in film speed during the first year of life is quite common and this is accelerated by increased temperature and relative humidity; careless storage under high temperature for as little as a week can reduce the speed by 50 per cent. In some cases the increased size of fog centres may give a temporary slight increase in effective sensitivity.

23

All these problems can be reduced by refrigeration, which is the only way in which can be stored for comparative processing over a period of time. In extreme cases the effects of chemical vapours or storage in wooden boxes (Russell effects) may affect the film sensitivity and fog level. strips

increase for a 1.2.2 Latent image regression. The latent image may show a slight short period after exposure but the general tendency is for a steady decline in effectiveness; this drop is fairly rapid for a few minutes and it is advisable to wait for at least 30 minutes after exposing the last of a batch of strips in order to allow the separate immediately, 10 latent images to reach equilibrium. Bromide paper is usually developed but for monochrome negatives processing should commence between 1 and 2 hours 11 For colour negatives the film speed standard calls for 5-10 days after exposure. 12 although this delay is not applicable to most professional practice. storage,

Lippmann Emulsion Typical Microfilm

Overnight

i

D 2 Density loss

2

4

6

8

10

14

12

Hours

TIME INTERVAL BETWEEN EXPOSURE & DEVELOPMENT Fig. 1.1

Latent image decay curves. (Storage at normal

room temperature).

Emulsions vary considerably in their regression characteristics;

fine grain materials

films require 1-3 days to achieve are the most susceptible indicate the possible need for 1.1 Fig. curves in decay image latent The equilibrium. may be less critical in this emulsions short-term storage. Other

and some micro-recording

standardisation of

respect, but

it

remains a factor for consideration in any sensitometric work. As a rule exposure, a further delay is an interval T between the first and last

there

of thumb, of 10 Tmay be allowed before processing. processes Pre-exposed control strips are supplied by film manufacturers for many regression. image latent arrest to essential is strips these of storage and refrigerated 1°C below For short-term storage (4-6 weeks) Kodak recommend a temperature necessary. is (0°F) 18°C below (30°F) but for longer periods a temperature to the storage In long-term comparative studies there are two possible approaches of control strips start of the experiment and to store them tor (1) To expose sufficient strips at the if

—

—

subsequent development as required.

24

To

store the batch of strips in an unexposed form and to expose them shortly before they are needed for processing. The choice is really between the risks, respectively, of latent image regression and pre-exposure deterioration of the film characteristics. Refrigerated storage makes (2)

both

methods

practicable, but the latter course is probably preferable if a good sensitoavailable. Experimental work on latent image regression and intensification

meter is has been reported by Gutoff and Timson. 13 It must further be ensured that the material is not exposed to light or stored near any radioactive materials. Any possibility of post-exposure latent image destruction (due to the Herschel effect, the Clayden effect etc.) must also be prevented. In the specialised case of autoradiography (see p. 300) the emulsion is in contact with the specimen, which may cause chemical effects on the latent image (negative or positive chemography). This may combine with normal latent image fading, background fogging and the primary exposure, causing problems in quantitative work. Colour films vary considerably in their susceptibility to image regression and the manufacturer should be consulted on the precautions necessary for critical long-term studies.

10'

LOG Fig.

P

y

6 (3) Bas c fea tures ° f Log ITxLog curves (simplified isodensity lines of exaggerated ! ,. intensity 0.1 lux). H, Intensity scale exposure of 0" 3 1 sec duration L Intensity at '° n DjWeal Iso-dansity iine f D °' = °-1- Q

.Measurement

LLI

Level

DISTANCE ACROSS

IMAGE

Fig. 2.13.

Emul s

™/

n - stem is

Eq. 3.3 a

s P ecia l

case in which several other factors

117

When

when A is ) The foot candle

A is measured in square metres the value for E is in lux (lm/m

measured

in square feet the value for

E

is

in foot-candles (lm/ft

2 ).

2

;

the unit of illumination commonly used in Britain and the USA; it is the illuminance given by a uniform point source of 1 candela at a distance of 1 foot and is equal to 10-76 lux. The basic photometric formulae (e.g. Eq. 3.3) apply to point sources, whereas many lighting units are broad sources. In illumination engineering, where the sources are often windows and trans-illuminated panels, formulae related to Eq. 3.3 are used to calculate the luminous flux necessary to achieve a specified illuminance on working surfaces. Factors such as the coefficient of utilisation for the lamp fitting and dirt (fc) is

13 depreciation must be included in the calculation. Fig. 3.6 shows illumination curves of the type often published for focusing spotlights. At a distance of 10 feet and at the full spot setting the central illumination is 10,000 lux, with a half-peak beam diameter of 6 feet. In the flood position the illuminis maintained over a beam diameter of 8 feet. The illuminance at lamp distances can be calculated by applying the inverse square law (Eq. 3.5).

ance of 3500 lux greater

SPOT

Position

Lamo

]

Distance 10ft

—-^FLOOD'

Position

2,500

10ft

AXIS

5ft

5ft

10ft

illuminance Fig. 3.6. Illumination curve showing the effect of focusing a spotlight. Spot position 1 0,000 lux centre-beam 3,500 lux centre-beam illuminance at 1 feet. Beam width feet. Beam width (half-peak) 6 feet. Flood position at 1 8 feet; half-peak width 15 feet. :

:

3.3.4 Luminance. Luminance is a measure of the light emitted from a surface.* This is normally due to reflected illumination, but the term also applies to selfemitting and trans-illuminated diffuse surfaces. *The word 'brightness' is often used in this context, but it refers, strictly speaking, to the visual sensation rather than to an objective property. Luminance is a physical quantity that can be measured by a reflectedlight exposure meter. Brightness refers to the mental response and cannot easily be estimated; it can vary with viewing conditions and certain psycho-physical factors. The terms ' subjective brightness or luminosity are preferable. '

'

:

The

S.I.

unit of luminance

is

:

the candela per square metre (cd/m 2 ),

known

as the

nit.

A unit commonly used in Britain is the foot-lambert (ft-L) an

ideal diffuser* emitting

1

lm/ft 2 ;

it is

this is the luminance of equal to 1/w candelas per square foot (0-318 ;

cd/ft 2 )or3-426nit. 3.3.4.1 Reflection factor. The light reflected illumination (E) and the reflection factor (p).

Luminance

(L)

from an

ideal surface

depends on the

=E x p

Eq. 3.4

The

factor p is the ratio of reflected to incident flux; for an ideal surface, p would be 1-0, but in practice the values found for diffuse surfaces range from about p=0-8

p=0-04 (black

(white paper) to about

The

cloth).

mentioned above would be a uniform diffuser, with a luminance independent of the viewpoint and lighting angle. All surfaces have a certain specular quality and exhibit different reflection factors under different conditions; the reflection factor (p) cannot therefore be assumed to be constant and the term luminance factor (jS) is sometimes used in this context. /3 is the ratio between the luminance of a surface in a particular direction and the luminance of a uniform diffuser under similar ideal surface

illumination conditions. In the case of specular surfaces

Methods based on exposure tions about a subject's

tables

luminance

/8 may be greater than 1-0. incident-light exposure meters make assumpbased entirely on its illumination. Despite the

and

variable factors p and 8 mentioned above these methods are successful in the great majority of cases: details are given in the standard works on exposure determination. 14 3.3.5

Factors affecting subject illumination.

When the luminous intensity (I) of a point source in any given direction is known (probably from a polar diagram such as Fig. 3.4), the illuminance (E) on a plane normal to the beam at any distance (D) can be calculated 3.3.5.1 Inverse square law.

Extended sources give a more gradual fall-off in illumination; for a line source of can be shown that E=I/D. 3.3.5.2 Cosine law. If, as shown in Fig. 3.7, a light beam of cross-section BB falls at an oblique angle 8 to a surface, it illuminates a larger span AA; the luminous flux is thus spread over a greater area and the illuminance (lumens per square metre) is reduced. The ratio of BB/AA is equal to cos 6 and the illuminance is therefore reduced in proportion to cos 6. This is termed the cosine law and its significance for oblique lighting angles can be seen from the cos 6 values in Table 3.3. 3.3.5.3 Cos 3 law. If a plane surface is lit by an overhead point source (Fig. 3.7b) the corner illumination is less than that at the centre for two reasons infinite length it

(1)

SC

is

greater than

(2) 6 C is greater

The combined cos 3 9 law, which

*A

SA

(inverse square law).

than # a (cosine law).

effect

may

of these obliquity factors for off-axis rays be derived from Fig. 3.7b as follows:

uniformly diffusing surface

is

one that appears equally bright for any viewing

is

expressed by the

direction.

119

Oblique Perpendicular

Illumination

Illumination (9 = 0°)

B

B

——

(6=60°)

B

1

Beam Width

Illumination

Angle tf

(a)

Illuminated Surface

Width

I

(b)

Fig. 3.7.

Cosine laws of illumination,

(a)

Cosine law

:

(AA= B B/Cosfl. Cos 60° = 0.5

Illuminance at

(1)

.

AA= 2 x B B)

(b)

Cubed cosine

Ec

is

less

Because of the inverse square law, the corner illumination

Ea

axial illumination

by

V

-FCa xA SA2 — cp

However, SA/SC=cos

The illumination

SC 2 /SA 2

a factor

Jlc

(2)

.

9,

law.

C = llluminance at Ax cos 3 8.

so that

than the

.

E c =E a xcos 2

in the corners is oblique; therefore

from the cosine law:

E c =Ea x cos (3)

Combining

factors

1

and

2:

E c =E a X (cos 2

6)

x (cos

61)

=Ea

cos 3 9

Eq. 3.6

(E a ) is not known, the calculation can be made from the luminous intensity of the source (I a) and the source-to-surface distance (D):

If the axial illumination

axial

la

E»=The cos 4

9 law,

which

is

D

Eq37

2

related to the above effects, describes the theoretical fall-off 12 an optical image (see p. 64).

in the illumination in the plane of

120

xcos 3

TABLE

3.3

COSINE VALUES Angle

10°

20°

30°

40°

50°

60°

70°

80°

0-98

0-94 0-83 0-78

0-87 0-65 0-56

0-77 0-45 0-34

0-64 0-27 0-17

0-50 0-12

0-34

0-17

004

06

001

—005

8

cose cos 3 9 cos 4 e

10 10

095

1-0

0-94

90°

9 law). A single point sometimes used for illuminating a relatively large area (e.g. contact printing). Reasonably uniform illumination can be obtained only when the subtended angle 9 at the corner of the field is small. This can be achieved by using a large source-to-film distance, but it is inconvenient and wasteful to have the source too far away, so it may be useful to calculate the nearest distance required to satisfy a certain criterion of

3.3.6

source

Calculation of the evenness of illumination (cos 3

is

uniformity. It

might be decided, for example, to accept a 5 per cent loss of illumination in the field, which implies that the cos 3 9 factor should not be less than 0-95.

corners of the

tane.|£

Fig. 3.8. Illumination

Fig. 3.8

shows a

find the distance (1)

The

(2)

where cos 3 0=0-95

= ^/0-95 = 0-983:

The source

From 10|°

diagonal of 20 in. (AC where cos 3 /_ASC=0-95.

field

SA

limiting angle 9

cos 9

from

a point source.

= 10 is

in.).

The problem

in this case

is

to

given by:

9 is therefore 10i°

distance (SA) can

the preceding figures

= 10in./0-185=54in.

now be found from SA=AC/tan

AC = 10

in.

and 6=\Q\°, so that

9:

SA=10

in./tan

It can be seen that a point source distance of about three times the field diagonal necessary to give a cos 3 # loss of less than 5 per cent.

is

121

—

:

The more complex sources 3.3.7

a

is

calculations necessary to find the illuminance given by multiple

common requirement in architectural design and

other

fields.

8

15

10

9 >

>

>

Exposure calculation from illuminance data. For photographic purposes

the essential items of illumination data are (1) The illuminance level (in lux or foot-candles). (2)

The beam

angle.

This information may be given by the manufacturer in numerical form (Table 3.4) or by an illuminance curve (Fig. 3.6) or as an exposure guide number. Alternatively, the illuminance may be calculated from luminous intensity data using Eq. 3.5 or Eq. 3.7. TABLE 3.4

ILLUMINATION FIGURES FOR TYPICAL PHOTOGRAPHIC LIGHT SOURCES (230V LAMPS AT A DISTANCE OF 6 FEET) Centre-beam illuminance

Lux

Foot-candles (lm/ft

2

)

(Im/m 2 )

W

Photoflood No. 2 500 Bare lamp* In flood reflector In spot reflector Reflector 'Photolita' lamps

275W Type SMt 500W Type NMf 375W Type KMf Clear

300

320 1400 3000

90 220 360

900 2200 3600

32 140

Beam

noon sun (mid-summer) 8000 800

United Kingdom Cloudy dull noon (U.K.)

diameter

(half-peak)

80000 8000

8 feet

4

feet

7 feet 7 feet

3J

feet

—

•Calculated from total lumen figure (145001m). tFigures derived from Philips polar diagrams.

A general formula 16 may be used for exposure determination once the illuminance (E)

is

known: ,

__

'

^

/Exposure time

(sec)

XE

(fc)

X S (ASA

film speed)

_,

3 g

20

W

photofloods quoted in Table 3.4 is to be used at a Example: One of the 500 and the ft (giving an illuminance of 300 fc). Film of 125 ASA is to be used exposure time is to be 1/50 sec.

distance of 6

„, . /1/50X 300x125 = , /-number =/sf -LV37 -5 xf/6 -3 ,

—^

The formula may be re-arranged

to find the illuminance (E) necessary for given

working conditions.

w™ =g

Illuminance required (E)

20 x (/-number) 2

xposure

^nie x ASAfilm^peed :

^

Fn ,*"q

Additional factors, such as the lighting angle, the subject reflectance and its surroundings will influence the exposure required in practice but these formulae may give a general guide for planning purposes. 122

3.3.8

Guide numbers. In

flash

photography the required lens aperture (/) is usually number and the desired flash distance (D).

calculated by the manufacturer's guide

GN=Dx/

Eq. 3.10

Typical flash bulb guide numbers for both feet and metres are quoted in Table 3.9. The guide number for a flash of known luminous energy (Q) can be estimated for a film of given ASA speed (S) by use of the following formula:

GN=V0-004xMxQxS

M

is

a reflector utilisation factor with a value normally in the range from 4 to 8.* is taken to be 6, the expression can be simplified for most purposes

If the value for

M

as:

GN=0-15VQxS Example:

If

Q

is

40.000 lm-sec. and S

is

100

ASA

the guide

number would be

calculated as

GN =0 assumed above that

•

1

5

V40,000x 100=300

luminous energy is used but where fast shutter speeds are necessary to reduce image movement, the value of Q has to be re-assessed. Published guide numbers normally take into account any losses due to emulsion It is

all the

make certain assumptions Standard reflector performance, covering the whole lens field. A subject of average reflectance in a medium-sized room with light ceiling and

reciprocity failure, but necessarily (1) (2)

walls. (3)

(4) (5) (6)

Negligible image magnification factor

(M + 1)

The angular cone of light accepted by the objective The medium between objective and subject, and The wavelength of light used (A).

Abbe's theory of resolution considers adjacent points in the subject as similar to lines in

a diffraction grating and suggests that to resolve the points the objective must accept at least two of the diffracted rays including the zero order ray. Fig. 5 6 shows the conditions for resolving two such points with axial and oblique illumination. In the (a>

Diffracted

Ray

Fig. 5.6.

.

these values are identical.

Condition tor the objective to accept a

first

illumination at angle

order diffracted ray (a) with axial matching objective aperture.

lumination (b) with oblique

ill

165

s

:

of the first order diffracted ray accepted is twice that with Abbe quoted the separation of two points which can just be resolved as:

latter case (Fig. 5.6b) the angle

axial illumination, indicating better resolution.

S=vt^t with

NA

axial illumination

or with oblique illumination, aperture

i.e.

with the illumination cone matching the objective

S =2

E ^ 5A

NA

Abbe's theory of resolution provides a simple, convenient formula and is widely An alternative formula, due to Lord Rayleigh, is derived from Airy's formula for the diameter of the diffraction image of a point (Airy disc). Rayleigh' formula for resolution, assuming illumination to match the acceptance cone of the accepted.

objective

is

„

1

_ Eq

-22A

S=2NA

~

.

5 2 '

-

Although the figures produced from Abbe and Rayleigh's formulae differ by 22 per cent this is neither surprising nor very significant when it is considered that we are dealing with detail which is either just visible or just not visible and there is no clear-cut division between these two states. The nature, in particular the contrast, of the object points will almost certainly make a practical difference to resolution. The figures relate to maximum theoretical resolution and are not necessarily achieved in practice (see also Chapter 2).

The important feature of these formulae is the agreement that resolution improves proportionally with shorter wavelength and higher NA, and that the best resolution is obtained when the illumination cone matches the angular aperture of the objective. 5.1.4 Useful magnification. Human eyes differ in their ability to resolve fine detail and the viewing conditions and nature of the subject influence the visibility of such detail. However, it is generally accepted that under ideal conditions a good eye might be expected to resolve points which subtend an angle of 1 minute arc. This corresponds at normal viewing distance of 250 mm. Fig. 5.7 shows other to a separation of 0-072 standards of visible resolution in terms of angular and linear separation. The useful magnification of a microscope is that required to make the smallest detail resolved by the objective large enough to be resolved by the eye, whether viewed as a virtual image or projected and recorded photographically. In either case a viewing can normally be assumed, but in the case of a photographic image distance of 250

mm

mm

any enlargement of the negative must be included in the magnification. Taking Abbe's formula for resolution and working an example for a (typical x 10 objective) with green light (550 nm), we find that: x , resolution =.-, vf A •

=« —550 a ^ nm 2x0-25

= 1100 nm = 1-1 fim 166

NA

of 0-25

:

"

Minutes of Arc

Separation at 10 inches

Just visible to good eye under ideal conditions

0-0029

Practical limit of average eye

mm

250

0072 mm

1-37

under good conditions

0)r.

0-0058"

Visible to average eye with

medium

at

or low contrast

subject

0-01

3-4

0-25n

00116

Fig. 5.7.

In order to

1 -1

m

just visible to the eye (taking

arc as the standard) the magnification necessary 1

(1)

is

9/°72mm = 72

=66

one minute of

^ ^ ^ NA)

^

/an easily visible to the eye^taking 4 minutes of arc as the min =i90 =264 (or 1056 xNA). is

standard) the magnification necessary

We

mm

Standards of visible resolution with the naked eye.

make a separation of

To make the separation of 1

0-29

°^

can say that

A magnification of less than about 250 NA cannot make full use of the resolving power of the

b

objective.

A magnification of about

1000 NA is the maximum needed to make the resolved comraonl y termed the maximum useful magnification (MUM) and/'the Jfigure of 1000 NA is an easily remembered rule of thumb Further magnification beyond the will not reveal more detail in the specimen and is known as empty magnification. This is generally to be avoided as the image produced will be of a 'woolly' nature. A small degree of empty magnification "is however sometimes justified in order to make a detail larger and (2)

^f™

J

h

S

1S

MUM

therefore more easily the viewing distance is greater than 250 mm, e.g. when a photomicrograpn is projected as a lantern slide or enlarged for exhibition purposes the image size may be proportionally greater without empty magnification becoming apparent" 5. 1 .5 Depth of field. In any photographic record the depth of field is governed by the angular cone of light from an object point which is accepted by the lens and the criterion of sharpness applied. In photomicrography the sharpness criterion is related resolu tion this bein the ba sis of acceptable JC ( image sharpness at the § , and the angular cone is dependent on the objective and the refractive index of the medium surrounding the object. identified.

When

Mr™ MUM) f ?

NA

167

The depth of field of the

medium

is

given by the following formula where n is the refractive index may be different from the. value used in defining

in the object space {this

NA): 2 AVn 2 -(NA) "

Eq. 5.3

(NA) 2 If A, the

wavelength of light used,

measured

is

in

pm the depth of field (D) is found in

fi,m, also.

So for a

typical

10x/0-25

500 nm)

NA D

objective used with a specimen in air (assuming A £

=

VI -1/16

=

-8 /xm

1/16

but

if

the specimen

is

mounted

D

in

=

Canada balsam (n = l

W9/4-1/16

-5

approx.)

A2 nm

"""""'

1/16

Visual observation through the eyepiece provides an additional field depth arising eye, which can focus comfortably on the virtual image at and infinity. Instinctive visual refocusing gives a depth of any distance between 250

from accommodation of the

mm

field

equal to

—

a

-- where

M

is

the total magnification. If

M=100,

this is 25/mi,

total visual depth of field 33fim or 37/um, to be compared with 8 or 12/rni above. This accounts for some of the more critical requirements for photomicrographic

making the work.

Possible methods for increasing the apparent practical depth of field using multiple exposures or continuously varying focus position on a single exposure have been suggested. 8 9 10 The best of these uses a very narrow slit illumination at right angles to the optical axis which confines the light to the part of the subject in the focal plane. This method, which is similar to that described on p. 153 for macro work, can be applied only to subjects where illumination at right angles is practicable. >

>

TABLE

5.1

SPECIFICATIONS OF TYPICAL MICROSCOPE OBJECTIVES Typical object

Type

Magn.jNA

Achromat

3-5/0-07 10/0-25

25mm 5mmt

20/0-50 40/0-65 40/0-95 100/1-30 10/0-35 20/0-65 40/0-90 100/1-40

-5mm 0-5mm 0-3mm 0-15mm 2 -0mm l-0mm 0-2mm

(Oil) (Oil)

Apochromat (Oil)

168

1

1

mm

field diameter*

5mm l-5mm 0-8mm 0-4mm 0-4mm 0-15mm l-5mm 0-8mm 0-4mm 0-15mm

on eyepiece used. Useful limit may be higher especially with apochromatic objectives, manufacturers produce 10X objectives with about 10mm working distance.

*Practical figure depends f Some

Working distance

5.2 Optical

Components

5.2.1 Objectives.

The most important part of

the microscope optical system

is

the

objective.

A quick

glance through a manufacturer's list of objectives shows what appears at sight to be a bewildering selection, thirty or forty different examples being quite common. can, however, simplify such a list by reference to certain important characteristics. first

We

(1) Magnification. (2)

Numeral aperture. Working medium (air

or liquid— immersion oil, water, etc.). Cover glass thickness. (5) Mechanical tube length. (6) Degree of correction: (a) Colour; (b) Flatness of field. 5.2.1.1 Primary magnification (nominal) The nominal magnification or power of an objective (as defined on p. 162) is engraved on its mount. This is the magnification of the primary image when the objective is used at its intended tube length. Actual values may vary slightly from those marked, and can be checked by comparing the image of a stage micrometer with an eyepiece scale. 5.2.1 .2 Numerical aperture. The NA (see page 1 64) is usually marked on the mount, immediately after the magnification and separated from it by an oblique g' line, e 10/0-25. In this case the NA is 0-25 which is typical for a 10 x objective. The NA and magnification of a microscope objective are analogous to /-number and focal length (3)

(4)

of a lens in ordinary photography. 5.2.1.3 Working medium. Practically all medium and low power objectives are intended to be used 'dry', that is with air as the medium immediately in front of the objective, the being dependent only on the half angle of acceptance