Precise Digital Exposure 129

Precise Digital Exposure Zone System Based Spot Metering for ETTR (The Ansel Adams’ Principles Applied to Digital)

Copyright © L. Anders Loof Hong Kong 2011, Seoul 2014 Available at andersloof.com

Precise Digital Exposure Zone System Based Spot Metering for ETTR

Front Cover: Cover: Covered footbridge in Yu Yuan Garden. ISO 50 1/15s f/8, hand held, Pentax Digital Spot Meter. Leaf AFi-II 12 on Rolleiflex Hy6 and Schneider AFD Xenotar 80mm f/2.8 PQS. E/S/H -0.7/100/100.

Image 1. Overlooking “Pavillion in Lake Center”, the oldest teahouse in Shanghai and ziczac bridge from xiaolongbao dumpling restaurant. ISO 50 1/80s f/11, hand held. Pentax Digital Spot Meter, Leaf AFi-II 12 on Rolleiflex Hy6 and Schneider AFD Xenotar 80mm f/2.8 PQS. E/S/H +1.0/100/70.

Note for All Images: All images in this paper were made at Shanghai Shangh ai Old Town, or Laocheng Laoche ng Huang Miao (Old City God’s Temple) area with its Yu Yuan Garden in Shanghai, China. This area features historic Shanghai architecture and market areas, famous xiaolongbao dumpling and other traditional restaurants, restaurants, temple, old teahouse with nine turnings zigzac bridge, and the famous 400-year old Yu Yuan Garden. Yuan in Chinese means garden, and Yu means pleasing and satisfying. It is one of many favorite places for me to visit in Shanghai. Living as an expat in Asia, Shanghai is like a hometown and no less so by being married to Shanghainese.

All images in this paper were processed proces sed using Capture One. No Photoshop Photosh op and no HDR was used. Exposure/Shadow/Highlight Exposure/Shadow/Highli ght adjustments are annotated for each image as E/S/H. Precise Digital Exposure.pdf / andersloof.com

Copyright © L. Anders Loof Hong Kong 2011, Seoul 2014


CONTENTS

FOREWORD

1

INTRODUCTION

2

1.

5

THE PROBLEM AT HAND – PRECISE DIGITAL EXPOSURE

2. WHAT IS THE ZONE SYSTEM? Origin of the Zone System (and the Misconception of What It Is) Visualization and Image Values A brief on the Fundamental Basis

7 7 8 9

3. THE DIGITAL ZONE SYSTEM Middle Tone 13 Scale of the Zones Dynamic and Textural Ranges The Zone Scale for Leaf AFi-II 12 (Aptus-II 12) Expansion and Contraction Characteristic Curve The Histogram Effect of ETTR Effect of Curve Adjustments

13 14 14 15 18 19 23 24 25

4. PRECISE SPOT METERING FOR A DIGITAL SENSOR Visualization 27 Spot Metering Simplified Precise ETTR with In-Camera Spot Meter

27 27 29

APPENDIX - COMMENTS ON SOME TOOLS Leaf AFi-II / Aptus-II Capture One Optional Spot Meters

31 31 31 32

REFERENCES

32

PUBLICATION AND COPYRIGHT INFORMATION Copyright 2011, 2014 by L. Anders Loof, website andersloof.com, personal E-mail [email protected]. Original draft was copyrighted in 2011, and was at time reviewed by Michael Reichmann of Luminouslandscape.com. The 2014 edition has minor updates and edited wording. This document is published on andersloof.com and is not for sale except by the rightful copyright owner. This document or any information therein may not partially nor wholly be incorporated into any other document or distributed without permission or explicit and legal agreement with L. Anders Loof.

Precise Digital Exposure.pdf / andersloof.com



FOREWORD

As a photographer I primarily picture landscapes and traditional lives, plus some select portraiture in studio. Having started off with film photography and transitioned into digital, some of the aspects in digital photography that I have attempted towards to master is the achieving of precise exposure for high dynamic scenes in landscapes, a pleasing transition into highlights similar to films, and the visual perception of there being light in a picture. For the latter two I have read books on traditional painting in order to try to gain a comprehension for how the appearance of light can be emulated also for the RAW converted image in a digitally captured scene. The first, precise digital exposure using Zone System based spot metering is presented in this publication. In addition to the above I value pleasing colors from a capture media. While Fuji Velvia 50 was my favourite film, it is first with my third digital back, an 80MP Leaf AFi-II 12 that I have experienced colors from digital capture to bring similar sensation of pleasing colors as Velvia did for my landscapes. These are not same colors as Veliva, but pleasing to my eye. I exclusively use Capture One for the processing of RAW images because it enables my brain to function with a photographic focus on the image. I typically do not use Photoshop. My personal experience from both film and digital photography is, that for most part, analogue techniques functions same for digital as for film, and with more control and more enjoyment of the photographic process. My hope is that what I present in this publication will be of value to other photographers, for a precise control of the latitude of todays digital sensors versus the dynamic range of a scene.

Anders Loof Seoul 2014


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INTRODUCTION

The subtitle to this publication may cause some to disclaim that digital requires different principles than are applied to analogue film, yet truth is that much remain same with digital as with film, if we consider that photography is fundamentally based upon the spectral response (response to light) of the capture media used. Ansel Adams through his Zone System developed principles for spot metering for the precise control of exposure for black and white negative film, Polaroid Land print film and more, and he envisioned its use for what he called the electronic image. “It has been said at various times that the advent of certain materials obviates the need for such a vehicle of thought and control as the Zone System. Such a statement reflects the misconception that the Zone System is useful only for relating subject luminance with print values as they occur with a specific set of materials. If the materials change, we do not discard the Zone System any more than we discard sensitometry (or our exposure meters, for that matter). A change of materials often does require adaptation in the way we apply the Zone System, but in no way eliminates its principles or usefulness in creative visualization. As long as we must be able to work from a range of subject luminances that are to be represented as we want them to be by a range of grey values (or color values) in print, the Zone System seems certain to provide an extremely useful framework.” … “ I eagerly await new concepts and processes. I believe the electronic image will be the next major advance. Such systems will have their own inherent and inescapable structural characteristics, and the artist and functional practitioner will again strive to comprehend and control them.” – (my emphasis) The Negative, pages xii, xiii

The fundamentals of The Zone System together with how Ansel Adams adapted it for blackand-white large format sheet film are presented in his book “The Negative” . When in 2008 I first read that book I found it remarkable that there are so many parallels between film and digital. In fact it made me conclude that film and digital in essence are much same, if at all traditional photographic means are used to explain. This publication aims to explain how the Zone System can be applied to digital photography for a method to spot meter in a scene for the deliberate and precise placing of the exposure latitude of a sensor compared to the dynamic range of a scene.

What precisely is the Zone System then? “The Zone System is a practical expression of sensitometry, the science that relates exposure and density in photography.” – Ansel Adams in The Negative, page 84 “After the creative visualization of the image, photography is a continuous chain of controls involving adjustment of camera position and other image management considerations, evaluation of the luminances of the subject and placement of these luminances on the exposure scale of the negative, appropriate development of the negative, and the making of the print.” - The Negative, pages 47-48


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It can be concluded:

The bare fundamentals of The Zone System are visualization and a precise control of the process, both of which aim at control of densities at exposure, throughout development and the print process.

The principles of Ansel Adams constitute the very basis for enabling the visualizing of an exposure based upon the latitude of any specific capture media compared to that of a scene. The principles are founded on having determined the characteristic spectral response of that particular media, and the spot metering at minimum one highlight (or shadow point) of a scene that is located towards the extremes of the latitude of that capture media. Thus what this publication describes is a precise method for digital exposure in contrast to live view or trialand-error exposure using ETTR, and which can be used to allocate exposure based on a single spot metered value. However, the Zone System facilitates also a basis for increased understanding of the control of densities captured for a picture. This publication thus describe the Zone System for control of the densities at capture in order to optimize the data to be available for the further steps of our craft to be made during the subsequent digital processing towards the print. For most scenes perhaps the in-camera averaging meter will be suffice and with a certain ETTR, however Zone System based spot metering provides a precise tool towards creative pre-visualizing and precise placing of the latitude of the digital sensor relative a dynamic range of a scene. “Control in photography depends upon accurate evaluation of the light and careful exposure of the film. Averaging exposure meters and automatic cameras give ‘acceptable’ average results…”, “…careful craftsmanship demands understanding of subject luminance and exposure considerations.” – The Polaroid Land Photography, page 118.

For further in-depth reading is referred to the References listed towards the end, and in particular the book The Negative by Ansel Adams. I express sincere and heartfelt thanks to Ansel Adams for his tremendous contribution to photography and for his development of the Zone System with Fred Archer. It is an honour to upon their basis of The Zone System be author of this publication.

L. Anders Loof Hong Kong 2011, Seoul 2014


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Image 2. Sun lit leaf in Yu Yuan Garden. ISO 50 1/30s f/8, hand held. Pentax Digital Spot Meter, Leaf AFi-II 12 on Rolleiflex Hy6 and Schneider AFD Xenotar 80mm f/2.8 PQS. E/S/H 0/50/100.


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1.

THE PROBLEM AT HAND – PRECISE DIGITAL EXPOSURE

Irrespective if analogue film or digital capture is used, light meters measure medium tone or middle grey, and in camera meters average an exposure for a scene based upon middle grey. Many cameras also utilize multi segments to average exposures more intelligent, while some apply measures to “extend” (or shift) the dynamic range of a scene, or we can manually apply exposure compensation for an ETTR (exposure-towards-the-right). The above works well until we wish to place the choice of exposure in our own hands by precise determining the exposure compared to the latitude of our digital sensor. With analogue photography in such situations we use spot metering, preferably using a 1-degree spot meter with which we can precise pinpoint in a scene. I maintain that nothing has changed in these regards and that for digital photography we can likewise apply a spot meter to precisely determine the exposure. However, the obvious needs to be stated, that the spectral response of a digital sensor does not match that of black and white negative film, slide film or other films. The digital sensor has a different width of exposure latitude and that responds with its own uniqueness towards the highlight and shadow ends. The characteristic curves for black & white negative and radiographic films are shown in Figure 1 and Figure 2, respectively. Figure 1 shows that for black & white negative film the maximum density is towards the left in the curve (shadows), and therefore it is for such film advocated to expose for the shadows for the collection of a maximum of densities for the negative. With digital photographic exposure we similarly have been taught to exposetowards-the-right, ETTR, in order to collect the most “pixel bucket” information with our digital sensor. In real use under changing light, the ETTR procedure is a trial-and-error method that lack precision and that therefore involves an inevitable “fudge factor”.

Figure 1. Characteristic Curve for Black & White film, reference: Ilfordphoto.com.


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Figure 2. Radiographic Film, Ref: www.sprawls.org

Very much same as for the radiographic film in Figure 2, all films and digital sensors respond to light with a spectral response. They therefore have a film specific or sensor specific latitude or response (dynamic range), with which they are capable to capture an image. The exposure is the time at which we determine where to allocate that exposure latitude compared to the dynamic range of a scene. A difference with digital sensors compared to film is that they have a more linear response. When processing an image in a raw converter, the highlight recovery sliders enable us to recover texture and color information also when one or two of the RGB channels have clipped, while similarly at the shadow end the recovery sliders enable us to recover texture and color information from the minimum of pixel data collected by the sensor’s pixel buckets. The simplest way to precise determine exposure for digital exposure is thereby by using a spot meter for the exposure point of a scene that will yield the brightest capture data utilizing all three RGB channels. Upon a single such reading we would precisely be able to determine that location of the latitude of our sensor in a scene. This will be based to some degree also on the software that we use for processing, which is part of the chain from the senor. Dependent on the dynamic range of a scene, we may wish to further control and to precisely determine also the following points as means to aid for our visualization of how to best capture a scene in front of us: •

•

The brightest point of a scene for which recovery of the last RGB channel turns into textureless white or RGB value 255. The darkest point before and/or after recovery sliders in processing, thereby with purpose to confirm the dynamic range of our capture versus that of a scene.

The above can be spot metered with much simplicity, and for the making of only one precise exposure of a scene. However, it requires to first having determined the precise spectral response of the digital sensor, much same as Ansel Adams did for black and white film and other film in his application of the zone system (e.g. in his book The Negative). If you would like to fast track, please jump to Chapter 4.


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2.

WHAT IS THE ZONE SYSTEM?

In the Introduction we concluded:

The bare fundamentals of The Zone System are visualization and a precise control of the process, both of which aim at control of densities at exposure, throughout development and the print process.

For black-and-white photography Ansel Adams taught us to expose for the shadows (and develop for the highlights) for the optimization of densities in the negative (in principle he applied ETTL, expose-towards-the-left). With a digital sensor we should for optimum densities or RGB values in our RAW file (in principle) expose-towards-the-right, ETTR. By applying Zone System based spot metering we can decide upon the digital exposure with pinpoint precision. Notably the Zone System thus relates also to our visualization of the image. Therefore when capturing an image we should decide on a desired result on basis of what will fit within the dynamic range of our digital media and with a mind towards how we visualize the completed picture. Thereby the Zone System offers still today a precise tool towards achieving a maximum of densities with richness in mid tone colors through textured high values and reduced noise in shadows and per our creative vision.

Origin of the Zone System (and the Misconception of What It Is) Ansel Adams developed The Zone System with the cooperation of Fred Archer in the 1940s. Because it was first applied to black-and-white sheet film photography, this is perhaps why it since frequent is misinterpreted, misunderstood and in publications limited to that method of how it was applied. Regrettably it appear a common misconception to apply it same and with same number of zones to other capture media including digital which is incorrect and incomplete. Until writing of this publication I am not aware of any other source which has based an application of the Zone System or spot metering for digital correctly as Ansel Adams advocated it could for any capture media – on the basis of the spectral response of the particular digital media. The very fundamentals of The Zone System are readily presented in Adams’ book The Negative along with application for a particular example media (black and white negative film). That book remains the authoritative source of The Zone System and is a part in a series of three; The Camera, The Negative and the Print, and which highlight the concept of a full process of visualization throughout control of densities to the print. Arguably there is also a fourth book the Polaroid Land Photography in which Adams further explained the application of The Zone System to a new media. The Practical Zone System for Film and Digital Photography by Chris Johnson stands out as a book that credibly describes digital in relation to the Zone System, however is not a complete in that application, as was Adams for blackand-white film in The Negative. With Precise Digital Exposure I attempt to show precisely how to apply the Zone System to digital similar as Adams did to black-and-white negative film and as he did for reversal films including Polaroid Land prints, and for the precise spot metering based upon the particular spectral response of a digital sensor. Precise Digital Exposure.pdf / andersloof.com

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Visualization and Image Values Ansel Adams emphasized the creative process in the craft of photography, and Chapter 1 in The Negative is titled Visualization and Image Values. The location of the chapter appear to emphasize the importance of visualization for The Zone System, and as a means to decide upon exposure per how one visualize the image will later appear in the negative through development and the print. With digital we can equal this with visualization for how the densities will be captured by the digital sensor at exposure, which enables us to optimize that information at exposure for arriving at a best utilization of image data later during processing (e.g. in Capture One), and in the end for optimized color and tonal densities for the completed picture and the print. “The concept of visualization set forth in this series represents a creative and subjective approach to photography. Visualization is a conscious process of projecting the final photographic image in the mind before taking the steps in actually photographing the subject. Not only do we relate to the subject itself, but we become aware of its potential as an expressive image. I am convinced that the best photographers of all aesthetic persuasions see their final photograph in some way before it is completed, whether by conscious visualization or through some comparable intuitive experience.” – The Negative, page 1 “The Zone System allows us to relate various luminances of a subject with the gray values from black to white that we visualize to represent each one in the final image. This is the basis for the visualization procedure, whether the representation is literal or a departure from reality as projected in our mind’s eye.” – The Negative, page 47

In essence, the above challenges the current trend towards preview on digital displays or EVF (electronic viewfinder), from point that we in such are presented with what appears a “completed” rendering of the image which may misguide us to how the image will appear after processing. The Zone System is a method to narrow down information into a discrete vision that we can see in our mind’s eye of tones and contrasts on basis of how they will be captured from a scene, which together with our experience will enable us to in our minds eye picture how they will appear after processing and in print. Thus the Zone System is a deliberate process that aims to break down image parameters into manageable pieces that aids to more clearly see and determine during the capture stage. Nowadays nearly every digital camera and back display a histogram, but unlike the Zone System these do not permit us to pinpoint and accurate determine the luminance within a dynamic range of a scene. A spot meter with the knowledge of the characteristic latitude of our sensor, which is founded on the Zone System, helps us to consider not only where to designate medium tone but the important of what tone in the scene we wish to be the highest value with texture, and allow us to also inspect for the lowest tone which we are able to capture detail in. For a scene that exceeds the dynamic range of our sensor we can thus make deliberate decision for how to best capture the scene. “Seeing the alternative renderings of a subject in advance provides great latitude for creative interpretation by allowing us to apply appropriate measures at all stages of exposure and processing to fulfil our visualized image. Once you begin the process of visualization, the final image becomes of paramount importance, and you are less concerned with the subject per se than with your representation of it. The image becomes the enlargement of experience of the subject.” – The Negative, page 2.

Ansel Adams worked much in black-and-white, which is mere one discretion of reality, and one in which perhaps more extremes of tones can be accepted as believable “accurate” interpretations. He also applied much dodge and burn to enhance his vision per his recollection of the experience of the scenes or his remembrance of the scene. Visualizing in tonal values has a clear relevance also in color photography because tones, contrast and Precise Digital Exposure.pdf / andersloof.com

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colors are among the fundamental image parameters we deal with. The luxury we have compared to what Ansel Adams is that we can apply more adjustments after capture than the ones he had at hand. In the context of visualization, Minor White in The New Zone System Manual divided visualization into to Pre-visualization, referring to the visualization when studying the subject, and Post-visualization, referring to the remembering of the visualized image at printing. Thus for digital we could in essence refer to Pre-visualization as visualizing an image for an exposure, and Post-visualization as when we during RAW processing recapture our experience from the scene into the processed image for the print. Along same line Ansel Adams referred to the negative as the score for a pianist, and the print as the performance, as to shed light that post-visualization can differ depending on when the artist presents it, or if the negative is put into the hands by another artist. I maintain that the case is same for digital and our RAW file.

A brief on the Fundamental Basis Application of the Zone System at capture requires spot metering of a scene, using preferably a 1-degree spot meter such as the discontinued Pentax digital spot meter. An in-camera spot meter can be used, but it should be used with caution since it averages a larger circle within the image. With the Pentax spot meter one can accurately determine all the EV (exposure values) within a scene and can thereby accurately visualize the contrast of the scene prior to making a capture. Using a spot meter one can accurate determine precise how or if it is possible to place the dynamic range in a scene within the exposure latitude of the media used. It should be reminded that any meter is also dumb, in that it assumes that the values measured are medium tone, or 18% grey (same as a Kodak 18% grey card, or close thereto). All meters are programmed in such a way, since this and the stops over and under medium tone are what exposure settings are based upon. In the Zone System, the Zones simply define the number of tonal values away from medium tone, or from what Ansel Adams defined Zone V exposure. To the far ends in the Zone Scales is the darkest black and whitest white where there is no visual texture. This scale and the number of Exposure Zones or stops from medium tone or Zone V exposure assist us to visualize the image at capture. However, we are of liberty to assign any tone in a scene to represent medium tone (18% gray), on the basis of how we wish the exposure scale to later appear in the print (applies to black and white film), or RAW file, and all other tones simply fall in place based on the Zone Scale. “Both Polaroid films and transparencies have a considerably shorter scale than conventional negative films, however. Few reversal materials will record detail above Zone VII, and even this may be beyond the scale of some. A series of tests should be conducted to determine the practical scale of the film used before deciding where to place important high values which must retain texture and detail.”- The Negative, page 97.

The Zone scale for black-and-white negative film by Ansel Adams is shown in Table 1. A comparison of it to Polaroid Land Photography is shown in Table 2. The point already made is that a digital sensor is yet another capture media for which we require to establish a spectral response. “The Zone System procedures described apply to the use of conventional black-and-white negative films, and with modification of scale, to color negative film. Reversal films (that is, those which produce a positive image directly rather than a negative) call for a somewhat different approach. Such films include transparency materials and Polaroid Land prints.” – The Negative, page 95.

“The procedure discussed with negative films was to expose for the shadows and develop for the high values, based on the use of exposure alone to control the low-density areas, and exposure combined with development to control higher densities. The same requirements apply with reversal films, except Precise Digital Exposure.pdf / andersloof.com

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that the low-density areas are now the high values of the subject, and the high densities represents the shadows. This will be apparent if you examine a positive transparency or a Polaroid Land print: the lowest deposit of silver (or dye if color film) is in the high-value areas, and minimum density represents clear film or pure white paper base. The high densities occur in areas corresponding to low-luminance subject values.” – The Negative, page 95-97.

We should note that Adams clearly points at control of densities (within the possibilities he had at hand, namely exposure and development), and which refers to a maximizing of densities captured during the exposure in order to achieve the best densities for the negative, development and the print. With the above and what has been said prior we can conclude:

Digital exposure should expose for the highlights or expose-towards-the-right, ETTR, in order to maximize captured density information , however should not blow any significant highlight information.

As a matter of interest, lets refer to how Ansel Adams applied the Zone Scale different for black-and-white negative film and Polaroid Land prints. In Figure 2 we can note that the highlight descriptions are shifted between the two medias. This is due to the adaptation of The Zone System to distinct different medias, however that Exposure Values remain (but have different meaning), and half scales are applied for Polaroid Land prints due to the shorter number of full stops in the scale. “At this point we have established the midpoint of the scale of exposures (Zone V), and negative values and print values (Value V). We also know from experience that reducing exposure will produce a darker print value, and increasing exposure will produce a lighter print value. To determine the remainder of the scale, then, we define a one-stop exposure change as a change of one zone on the exposure scale, and the resulting gray in the print is considered one value higher or lower on the print scale.” – The Negative, page 49

“Note that we use the term zone to refer only to the exposure scale, and value for the other concepts, specifically luminance values, negative density values, and print values. It is essential to remember the basic relationship: if we take a reading from a single-luminance surface and use the indicated exposure settings, we are giving Zone V exposure for that surface, and anticipate a negative density Value V and a print Value V (middle gray) representing that surface.” – The Negative, page 48

Accordingly, the key fundamentals of the Zone System scale are following. Medium tone, or Zone V (which is defined based upon 18% grey), is a pivot point and do not move on the scale. It is thereby the basis for all measures of exposure using cameras and the exposure for an image. However, any tone in a scene can be assigned medium tone exposure. Other Zones are in full stops but can also be half stops or partial stops and which designate their distance in Zones from Zone V, medium tone.


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Value Range

Zone

Low Values

Zone 0 Zone I

Zone II Zone III Middle Values

Zone IV

Zone V

Zone VI

High Values

Zone VII Zone VIII

Zone IX

Zone X

Description Total black in print. No useful density in the negative other than filmbase-plus-fog. Effective threshold. First step above complete black in print, with slight tonality but no texture. First suggestion of texture. Deep tonalities, representing the darkest part of the image in which some detail is required. Average dark materials and low values showing adequate texture. Average dark foliage, dark stone, or landscape shadow. Normal shadow value for Caucasian skin portraits in sunlight. Middle gray (18% reflectance). Clear north sky as rendered by panchromatic film, dark skin, gray stone, average weathered wood. Average Caucasian skin value in sunlight, diffuse skylight or artificial light. Light stone, shadows on snow in sunlit landscapes, clear north sky on panchromatic film with light blue filter. Very light skin, light gray objects; average snow with acute side lighting. Whites with texture and delicate values; textured snow; highlights on Caucasian skin. White without texture approaching pure white, thus comparable to Zone I in its slight tonality without true texture. Snow in flat sunlight. With small-format negatives printed with condenser enlarger, Zone IX may print as pure white not distinguishable from Zone X. Pure white of the printing paper base; specular glare or light sources in the picture area.

Table 1. The Zones for black-and-white negative film, The Negative, p. 60.

1

Exposure zone 0 I

2

II

Conventional Black-and-White Film Print value Description 0 Solid black I First step above solid black II First “texture”

4 8

III IV

III IV

16

V

V

32

VI

VI

64

VII

VII

Relative luminance units !

V VI VI! VII

High skin value, full texture

VIII

VIII

Highest textural value

256

IX

IX

Untextured white

III IV

II

Textural significance Average shadow value Middle gray—18% gray card value Average skin reflectance (36%)

128

Polaroid Black-and-White Prints (Approximate) Print value Description 0 Solid black I Solid black

VII! VIII VIII! IX

First step above solid black First “texture” Average shadow value Middle gray—18% gray card value Average skin reflectance (36%) High skin value Quite high value— reduced texture Usual texture limit Just below pure white Pure white Pure white

Table 2. Relationship of Exposure Zones and Print Values, Polaroid Land Photography, p. 129 (highlights added)


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Image 3. Window details, Yu Yuan Garden. ISO 50 1/20s f/5.7, hand held. Pentax Digital Spot Meter, Leaf AFi-II 12 on Rolleiflex Hy6 and Schneider AFD Xenotar 80mm f/2.8 PQS. E/S/H 0/50/50.


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3.

THE DIGITAL ZONE SYSTEM

The prior two chapters should already have set the path towards where we are heading, the application of the principles of Ansel Adam’s Zone System towards establishing the characteristic response of a particular digital sensor, and primarily the upper and lower extreme points (with and without highlight and/or shadow recovery). Thus in order to be able to spot meter one or more points in a scene, and upon this/these precise decide where to place the available latitude to the best of our vision for the capture of an image. Firstly we will establish the Zone Scale:

The three essential pieces needed for creating a Zone Scale: 1.

Middle Tone

2.

Scale of Zones

3.

Dynamic Range or Textural Range

Middle Tone Middle Tone or medium tone should correspond to the spot metering of an 18% grey card. It is the fundamental basis for exposure settings on any camera, and which Ansel Adams called Exposure Zone V. Accordingly this should be maintained as the pivot point for a sensor, or an anchor point. In our RAW processor this should equal the middle value, and in Capture One we can define it as equal to RGB 127 at default settings (midway between RGB 0 and 255), which we thereby can call RAW Value V , while we note that it corresponds to Exposure Zone V in a scene.

“Middle grey should be remembered by all photographers as a basic value, not unlike the key ‘A’ in music. On the scale of print values, a middle grey that matches the 18 percent grey card is defined as a Value V grey” – Ansel Adams, The Polaroid Land Photography, pages 128-129.

“Note that there is no fixed relationship between a subject luminance and a print value. Any subject luminance may be visualized as any print value; by placing the luminance on the appropriate exposure zone we may expect a print value that fulfils our visualization. The pivot point is middle gray; any subject luminance exposed on Zone V will yield a print Value V, which matches the 18 percent gray card used as a standard reference point” – Ansel Adams, The Polaroid Land Photography, page 129.


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Thereby, the essential is not to place this pivot point (Middle Tone or Exposure Zone V) on what appear as middle tone in a scene, in order for the middle tone in the RAW file or the print to represent middle tone in the actual scene. Instead the aim or goal should be to assign the ends of a Digital Zone Scale to where they are desired to represent a scene for the digital capture. Exposure Zone V (middle tone) will thus be located on the Zone Scale relative to the Exposure Zone upon which we select to define the location of the Zone Scale

Scale of the Zones Although the Zone Scale can be at half or third stops, lets make it simple and we hereby define it at one-stop increments from Middle Tone (or Exposure Zone V).

“To determine the remainder of the scale, then, we define a one-stop exposure change as the change of one zone on the exposure scale, and the resulting gray in the print is considered one value higher or lower on the print scale.” – Ansel Adams, The Negative, page 49.

Thus, our task will be to make a set of test exposures at one-stop increments and to visually inspect the RGB values of the RAW file at defaults in Capture One for tonal and textural information (or our RAW converter at choice):

“If these concepts are new to you, I strongly urge you to make such a series of exposures”…”Take an evenly lighted, uniform surface and make a meter reading from it. A surface with slight texture, such as a concrete wall or a closely woven fabric, is ideal. Use whatever exposure is indicated to make one negative [or raw file] , thus giving Zone V exposure for that surface, and then reduce the exposure one stop at a time to make Zone IV, II, II, I, and 0 exposures on separate negatives. Then proceed with exposure increase at one stop intervals to produce Zone VI, VII, VIII, IX, and X exposures.” – Ansel Adams, The Negative, page 51.

Depending on the dynamic range that our digital sensor is capable of, as was the case for my Leaf AFi-II 12 the low values may go below Exposure Zone 0 and to -I, -II and so on.

Dynamic and Textural Ranges Ansel Adams defined the Dynamic and Textural range s as per Table 3: Full black to pure white – Zones from full black to pure white in prints, a.k.a. textureless black to textureless white (or for digital blackest black with acceptable noise ratio to blown out white). Dynamic range – Zones from beyond pure black to below pure white. It should be noted that this range is not same as is common used to specify “dynamic range” for digital cameras and backs, and which appears to instead be the full black to pure white. Textural range - The range within which Zones convey definite qualities of texture and the recognition of substance.


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Table 3. Zone System Ranges, The Negative, page 52.

With digital we strive to have richness in color and tones and to minimize blown out white and black with too much noise. Therefore it appears appropriate to define a Digital Zone Scale upon the Textural Range, because at capture we should aim to meter for the extreme ends of the scene that based on the latitude of our sensor we wish to capture with adequate textural information and detail. Another reason is that the very highest values at highlight recovery beyond visual texture consist of perhaps only one of the RGB channels and which can display a color shift. Thus the end Zones of our Digital Zone Scale should be defined as the brightest and darkest Zones that will capture adequate textural information, and/or an acceptable amount of noise in the shadows of the darkest Zone, with and without the corresponding recovery slider to max.

The Digital Zone Scale is defined with end points being the brightest textural white and the darkest textural black with acceptable noise, with and without corresponding recover slider to max. Between these points are at one-stop increments from Exposure Zone V the intermediate tones.

At this point we should mention that at time for capture, pending on the scene we may wish (and perhaps also should) account for a margin at highlight end to be available for us to in processing form an adequate shoulder as a highlight transition using curves. Thereby, as a means to control the length of shoulder in post processing, we may wish to utilize as our highest spot metered value with three RGB channels, the point at which the digital shoulder begins at defaults in our RAW converter. This will be discussed when we later take a look at the Characteristic Curve.

The Zone Scale for Leaf AFi-II 12 (Aptus-II 12) On basis of the preceding it should be more or less defined how to develop a Zone Scale for a digital sensor. For my Leaf AFi-II 12 I did so by photographing a test target at incremental stops of exposure and with the back set to ISO 50 (my choice is base ISO), ICC Profile LF3 Product 5, Curve Aptus-II 12 Product , and grey balance preset as Flash (5400° K on AFi-II 12, but reads in Caputre One as shot as 5300° K). The choice for using the lowest ISO on my digital back is explained per my interest in using the Zone System for maximizing color and tonal densities and thus I utilized the ISO that similarly yields best color and tonal densities. The test should preferably be shot at or near daylight since this is what defines normal exposure (same as daylight film per say), and away from direct sunlight. My departure point was Exposure Zone V (middle tone) to match an 18% Kodak grey card, and per prior we have defined Exposure Zone V as equal to RAW Value V when reading the RAW file with defaults in Capture One. The test target included also a near medium tone grey textural subject, a ColorChecker Passport, and red, green and blue targets. It was photographed under a canopy during sunny blue skies, thus under what can be expected to not depart aggressive from daylight white balance. Please refer to Table 4 for a record of the test. Precise Digital Exposure.pdf / andersloof.com

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Table 4. Zone Scale testing for Leaf AFi-II 12 (colors refer to specific RGB channel)

The test images were later opened at defaults in Capture One, and the combined RGB values tabulated for each exposure of the 18% grey card. Thus these became the density values of the 18% grey card at each exposure and we label them as RGB 18%. Numbers in red, green or blue in the table indicate saturation and for which first HDR recovery in Capture One was applied and thereafter full exposure adjustment as means to verify what range of RGB 18% values could be recovered from the RAW file at the very extremes of the Zone Scale. RGB 18% values of around 5 to 250 were accepted as being within an acceptable range of density (chosen arbitrarily in order to rule out any inaccuracy or variance in values). It should be noted that all light meters are calibrated per the ANSI standards to produce images that are 18% grey or ! stop less than the 18% Kodak grey card. However in the case of my Pentax Digital Spot Meter and my Leaf AFi-II 12 the RGB 18% value at RAW Zone V was 127 and which is perfect mid-way between 0 an 255. For my particular sensor we can conclude following for a Digital Zone System textural range on basis of Table 4: -8 stops = Low limit +2" stops = High limit without adjustments to RAW +3! stops = High limit with highlight recovery adjustments to RAW In order to clarify, at choice we can chose our spot metered “none recovered highlight end” to be the value immediate at clipping of all channels (RGB 255), or at start of the shoulder at defaults in Capture One. The latter was my personal choice and is basis for 2 " in above. Precise Digital Exposure.pdf / andersloof.com

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Thereby the useable textural range appears to be about 10 stops. However, textureless black appear to occur at about -8 stops and textureless white at about 4 stops. Thereby the full black to pure white range appears to correctly correspond to what Leaf advertises as a 12 stop dynamic range for the AFi-II 12, please see Table 6.

Image 4. Traditional Chinese architecture. ISO 50 1/25s f/8, hand held. Pentax Digital Spot Meter, Leaf AFi-II 12 on Rolleiflex Hy6 and Schneider AFD Xenotar 80mm f/2.8 PQS. E/S/H 0/0/100.

On basis of Table 4 we conclude the Zone Scale for Leaf AFi-II 12 to be as per Table 5, in which the lower row is when opening at defaults in Capture One, and second and third rows are using recovery sliders (HDR recovery 100%) either way, and similar to Ansel Adams we can call them expansion and exposure adjustment, respectively. The arrows merely indicate that an expansion takes place due to the recovery and exposure adjustments to the RAW files.

Table 5. The Zone Scale for visual texture for Leaf AFi-II 12 (Aptus-II 12)


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The information in Table 6 is advised by Leaf for AFi-II 12. We can see that there is good correspondence with my own results, and that ‘dynamic range’ per Leaf instead equals what Ansel Adams referred to as ‘full black to pure white”, as expla ined above. Since the above testing was shot under a canopy under sunny blue skies there was a very slight bias towards a blue cast, however not suffice to affect the results. Further testing under direct sunlight however indicates that under daylight grey balance the red, green and blue channels appear to clip at about the same time.

Medium tone / correct exposure

Shot of an 18% reflectance gray card, exposed such that it falls at 0 relative f-stops.

Upper limit of dynamic range

Just below 3 stops and which is based on 255 as saturation RGB value.

Lower limit of dynamic range

8-9 f-stops below 0 rel. f-stops as defined by noise ratio.

Default WB (Gray balance)

Flash preset (5400° K) (it can be noted that daylight preset is also 5400° K).

RAW histogram

Yes

Histogram exposure meter

Shows the overall exposure f-stops above or below 0. Signify areas in the image that are starting to lose visually observed detail.

Vertical lines towards ends of histogram The data outside these lines can be retrieved using the HDR recovery tool.

Table 6. Exposure Information for Leaf AFi-II 12 (verified with Yair Shahar, product manager of Leaf).

Expansion and Contraction For black-and-white film Ansel Adams taught that by departing from normal development within limits, one could adjust the negative scale to achieve a range of densities that compensates for long or short luminance on the subject scale, or control of contrast. For black-and-white negative film expansion results in an increase of contrast, and contraction in a decrease in contrast. Things have changed only so much, but since with digital we are already given a very low contrast file in the RAW negative we typically only apply expansion of contrast, hence recover (not contract), and which stretches our Zone Scale as per Table 5. As should be obvious there are also other tools for modifying contrast in Capture One, however here we limit as example to the HDR recovery tools in Capture One and that appear as equivalent to expansion for film. Table 7 shows application of expansion (HDR recovery tools in Capture One) on basis of photographing a Tiffen/Kodak grey scale. In the red rectangles are expanded zones of this scale. As can be seen expansion for digital does not mere effect the High Values as was the case for black-and-white film, and we can note that when the Highlight or Shadow HDR slider is applied on its own up to 100% in Capture One also the Middle Values are affected. On other hand when applying both the Highlight and Shadow HDR sliders at 100% the Middle Values appear reasonably without change. The number of stops of possible expansion is noted in red in the table and the arrows indicate the relative expansion.


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Together with prior sub-chapter this shows that pending on the dynamic range of a scene we shall for digital Expose for the Highlights and ideally Process for either Highlights or for both Highlights and Shadows.

Table 7. Expansion for digital using Highlight and Shadow HDR Recovery Tool

Characteristic Curve For film a characteristic curve shows the relationship between exposure and density of the negative or slide, and we can similarly develop a characteristic curve for the Leaf AFi-II 12 or any other digital back or camera by plotting the Exposure Zones versus densities in RGB values. It is possible that some may say that what was measured for film was the density of the negative or Polaroid Print, but does that really matter? What we wish to obtain and require a measurement of is the best quality RGB values and we can thereby call them densities (also to be compared to Figure 2). As an example lets first look at the characteristic curve for Fuji RVP slide film (Velvia 50), see Graph 1. The graph display the characteristic density values of the pigments on the film, hence the highest density values are for the dark areas that have more pigment on the slide, and low density where maximum light is permitted to transfer through the slide. Referring to The Negative page 86, Ansel Adams stated that 0.3 log Exposure units equals to one stop. Thus I have applied the added tick marks under the horizontal axis and a Zone Scale. We also Precise Digital Exposure.pdf / andersloof.com

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know that RVP’s exposure latitude is roughly -3 to +3 stops, or Zones II to VIII. Therefore as a visual guide we add blue vertical lines to indicate the borders for that latitude and place the rightmost such line at 0.0 log Exposure units. If we now inspect the curve, within most of the exposure latitude the curve is steep and forms nearly a straight line. The slope within this region of the curve indicates the Gamma or contrast of the film. For a given exposure difference within this slope there is a maximum difference in density, or what can be said to be a maximum separation in tonal and textural values. Those account for the important spatial separation of densities or tonal values in the image.

Graph 1. Characteristic Curve of Fuji Velvia, ref: Fuji Data Sheet (additions made as explained in the paragraph above).

With further review of the RVP characteristic curve we observe that the ends of the curve have curvature and fall also outside the perceived exposure latitude for the film. Within these curvature there is gradually less slope and thus if the film is exposed in these regions there is lesser separation or change in tonal values or texture for a given change in stops (if texture at all is visual). This is why with film we prefer to expose within the near straight portion of the curve, in order to achieve a maximum separation of and change in tonal values and texture (think black-and-white negative film which is exposed for the shadows and developed for the highlights, thus that there should be caution with such film to locate a zone on the shadow curvature which will later be brought up on the zone scale by developing the negative for the highlights). However, it is also this curvature at the highlight end that is of aesthetic value for film, including for RVP, as a transition into the brightest highlight. It is also important there because our eyes are initially more sensitive or drawn to the highlight regions when viewing an image, than to the shadows. With the highlight areas having lesser separation, there is a lesser or slower density change per stop, and which compresses the highlight areas to form a gradual highlight transition into pure white. With digital on contrary we often speak of a sudden clipping towards highlights because there is not much length of transition. Thus with digital per say we need to struggle to avoid fast clipping of highlights and should therefore adjust in the curve tool to provide for some shoulder in order to achieve a similar pleasing transition as film . With RVP we should in Graph 1 note that this important highlight transition occurs between approximately Zones VII and IX, say around one and half stop within the exposure latitude of RVP.


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Graph 2. Characteristic Curve as per tests for Leaf AFi-II 12 (RGB 18% values on vertical axis, and stops and RAW Values on horizontal axis), HV indicate High Value and LV indicate Low Value expansions. Normal indicates at defaults in Capture One.

Graph 3. Density Change per stop versus Zone Scale (based on same data as the Characteristic Curve in Graph 2).

Let us now look at a characteristic curve for the Leaf AFi-II 12, which is developed directly based on the Exposure Zones instead of using a log exposure scale, and by using RGB 18% values as densities, please see Graph 2. In order to have suffices accuracy the curve is based on " fractions of stop. The low density is defined as 0 and highest density is defined as 255. In that graph, Normal is when brought in at defaults into Capture One, while HV* is when applying the HDR Highlight Recovery Tool, LV* is when applying the HDR Shadow Recovery Tool, and LV** is when additionally applying -2.5 exposure adjustment to LV* . (LV* + HV*) is Precise Digital Exposure.pdf / andersloof.com

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applying both Highlight and Shadow Recovery Tools. Contrary to the RVP scale this curve shows the highest density where highest saturation of RGB 18% density values occur, or in the brightest areas of an image, since for those regions there is a maximum saturation of sensor or our maximum density. Therefore the characteristic curve is sloping in opposing direction to RVP.

Image 5. Historic building in Yu Yuan Garden. ISO 50 1/55s f/8, hand held. Pentax Digital Spot Meter, Leaf AFi-II 12 on Rolleiflex Hy6 and Carl Zeiss Distagon 50mm f/4 FLE HFT PQ. E/S/H 0/50/50.

Additionally, let us also look at Graph 3, which is based on same data as Graph 2, however is a graph of the gradual density change per stop on its vertical axis. The grey portion of the curve is a shading to indicate an assumption (or guess) that below a gradual density change of around 25 per stop is below a minimum for what we would like to strive for in order to have an acceptable separation in the more important areas of an image, or the non-shadow areas of an image. Since the separation of Low Values (shadows) can be viewed as of lesser importance than the separation of Middle Values (and indeed we have much more shadow information than does RVP), we should nevertheless note that we may wish to be cautious to at exposure place Middle Values below Zone II or III, or -3 or -2 stops below Zone V. Per inspection of Graph 2 and of within the black rectangle in Graph 3, the lesser separation and density change from around those stops and lower may not be desired if we later aim to bring those Exposure Zones up in the Zone Scale during processing. However, let us remember also that we already have a lesser density information to work with for processing in Lower Values than in other zones (due to that lesser pixel information collected into the pixel wells toward the lower ends of the Zone Scale).


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At same time we should take note that compared to RVP the highlight transition (shoulder) of the AFi-II 12 curve occurs over # stops or even less, and which in comparison to RVP is short. This indicates that pending on the light in a scene it can be important to not only maintain that shoulder but that we at decision for exposure should consider to expose with suffice margin on the highlight end to allow in processing for us to lengthen the highlight shoulder beyond one stop by using curve adjustments. Thus to in processing be able to create an adequate highlight transition that is as gradual as for RVP, but that the need for doing so will depend on our particular visual interpretation of the highlight zones and Exposure Zones in a scene. We can thereby conclude that it may in fact not at all be correct for us to ETTR to the far right of the latitude of the sensor:

In order to create an important shoulder for highlight transitions, ETTR should not necessarily be used to the maximum “permissible” to the right, and instead there should be given suffice margin at exposure for an adequate shoulder to be created using curve adjustments during processing. A deliberate decision needs to be made at capture on basis of the specific scene, if to assign one stop or more as a margin, upon which to be able to create a highlight transition using curves in post.

When assigning a high contrast scene within the exposure latitude of the sensor, the appropriate exposure on the highlight end of the Zone Scale may thus well be same as for RVP slide film (based on 18% grey exposure), but with the shadow values allowing for more detail over a larger number stop. As a matter of fact, with this reasoning, for a very high contrast scene we may need to consider placing middle tone on one or two stops lower than Zone V, and which compared to neutral (middle tone) exposure is shifting the histogram one or two stops towards the left! With above as basis, an example for when we should fully apply ETTR can be a low contrast scene for which we may wish to expose to the very beginning of the “normal” shoulder because there exist no need for an expanded shoulder transition for rapid change into very bright light values in such a scene. Hence we can ETTR to +2 ", +2 #, or maybe even +3, yet referring to the characteristic curve we may need to be cautious placing High Values of a scene within the shoulder due to separation or the lower gradual density change. Referring to Graph 3 for a low contrast scene it may not be necessary to push it too far to the right since not much will be gained and pixel information for a low contrast scene can be assumed to be suffice away from the lower zones of the Zone Scale. It should be noted that none of the above discards the use of ETTR, but on contrary brings us a precise tool for application of ETTR (or the Zone System as did Ansel Adams), and pending on our decision the consideration for the highlight region. It is worthwhile in relation to the above, to point out that with the Zone System we consider each Zone containing an averaged tone within a region along the characteristic curve, thereby e.g. Zone V is actually stretching from Zone V – ! stops to Zone V + ! stops if using " stops whereby adjacent to Zone V we have Zone IV** and Zone V*. This is important in considering placing an Exposure Zone at a limit, since it extends ! stop further. Per inspection in Graph 2 however, " stop appear adequate fine gradation compared to the curve, but full stops would have been a coarse measure considering the end regions.

The Histogram A histogram is a graphical representation of the tonal distribution in an electronic image and plots the number of pixels for each tonal value on a scale of 0 to 255. However as can be concluded on basis of the Characteristic Curve, the stops on a Zone Scale do not translate to an even number of increments on the 0 to 255 scale of the histogram. It would nevertheless Precise Digital Exposure.pdf / andersloof.com

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be helpful if a histogram would be made annotated with at least some basic information relating to Zones or adequate exposure information on basis of stops. Yet, the information from a histogram would nevertheless be incomplete compared to spot metering based on the Zone System, since a Characteristic Curve and Zone Scale provides us with important information for accurate and precise control of exposure beyond the capability of a histogram. In fact, using spot metering with the Zone System and for a specific digital sensor on basis of a Zone Scale or Characteristic Curve, exposure can be made solely based upon the spot meter and without a histogram.

Image 6. “Pavillion in Lake Center”, the oldest tea house in Shanghai, across from Yu Yuan Garden. ISO 50 1/60s f/8, hand held. Pentax Digital Spot Meter, Leaf AFi-II 12 on Rolleiflex Hy6 and Carl Zeiss Distagon 50mm f/4 FLE HFT PQ. E/S/H 0/0/100.

Effect of ETTR As we know from Michael Reichmann’s article from 2003; http://www.luminouslandscape.com/tutorials/expose-right.shtml, ETTR is an exposure basis to shift exposure towards the right but to avoid much blown out white. We may thus wish to ask if there is any negative effect from applying this method to the contrast of the image. This can be tested per photographing a Tiffen/Kodak Grey Scale card at varying exposures. Having done so for my AFi-II 12 at varying exposures from 0 to 2** (2#) stops above Exposure Zone V and at " increments, I thereafter brought the exposures back to my reference Exposure Zone V by using Capture One exposure adjustment tool. My conclusion is that there is complete correspondence with densities when using ETTR compared to without ETTR, please see Graph 4. The only exception is when the brighter tones of the chart plus the ETTR compensation exceeds 3** (3 #) stops and which we can note corresponds well with when in Graph 2 the characteristic curve reach the very maximum high value with expansion and Precise Digital Exposure.pdf / andersloof.com

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maintained tonal values. Caution is thus advised not to ETTR into the shoulder of the Characteristic Curve in order to have some margin.

Graph 4. Effect of ETTR.

Effect of Curve Adjustments Finally, lets also take a look at how curve adjustments in Capture One effects the characteristic curve. Here we base it upon the Tiffen/Kodak Grey Scale, for which curve 0 is without curve adjustments. The red and blue curves have applied half a grid in Capture one upwards and downwards at half point of the scale, respectively. The grey dotted curve has applied a quarter of grid downwards and upwards in its quarter points to form a S-curve. To note is that at the highlight end there is a shift with near +/-15 RGB densities and which equals " ~ ! stop.

Graph 5. Effect of ETTR. Precise Digital Exposure.pdf / andersloof.com

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Image 7. Gentlemen in “Pavillion in Lake Center” the oldest tea house in Shanghai. ISO 50 1/20s f/5.7, hand held. Pentax Digital Spot Meter, Leaf AFi-II 12 on Rolleiflex Hy6 and Schneider AFD Xenotar 80mm f/2.8 PQS. E/S/H -0.9/100/100.


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4.

PRECISE SPOT METERING FOR A DIGITAL SENSOR

As per previous chapters, precise exposure using spot meter for digital is much same as for film, but the rather obvious is that it require to establish our particular sensor’s spectral response (response to light), and primarily at the extreme highlight and shadow ends, with and without recovery applied in post processing. With this information we can use any of these points to precise spot meter a digital exposure for our particular sensor. The usefulness is in situations when we wish to precise locate the latitude of the sensor, compared to the dynamic range of the scene.

Visualization From Chapter 2 we remind that the important is visualization and control of the process , both of which per Ansel Adams aim at control of densities at exposure, throughout development and the print process. We can thereby apply the approach by Ansel Adams, to at capture visualize, or pre- visualize, how our exposure decision best can capture and artistically interpret the contrast range of a scene, within the latitude of our sensor. In simple terms, we can effectively spot meter for one of the highlight ends of our sensor, and allow the shadows to fall where they will fall. However, we can utilize more of our knowledge of the latitude of the sensor in our previsualization and may include in our decision for a margin at the highlight end to preserve the shoulder of our sensor, or an extended such to account for a gradual shoulder as highlight transition to be made using curves in post processing. Likewise we can at a scene spot meter for precise where our shadow end of capture will fall, without and after shadow recovery applied in post. Later under our control at processing we can adjust the RAW file per our recollection of the scene, or post-visualization , in order to arrive at a picture per our remembrance and recollection of the scene as it appeared in our minds eye at previsualization, thereby per our remembering and perception of the scene and interpreting it per our aesthetic vision. Such representation does not need to be technically correct as a true representation of the original scene in nature (which one can argue is not even possible), but it should with our media as a tool constitute a believable representation of our view, vision, impression and feelings of the scene. As Ansel Adams said, the negative is the score and the print is the performance.

Spot Metering The point with spot metering is that it is precise. A designated one degree spot meter is more precise than the spot meter in a camera which measure a larger area and will need to be used knowingly of the larger spot metering area. If we revisit the Characteristic Curve for the sensor in my digital back (Graph 2), we can note the following values: Precise Digital Exposure.pdf / andersloof.com

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+3! stops

Highlight recovery when all RGB channels clip

+2" stops

Max Highlight from all RGB channels

0

Medium tone

-4

Min Shadow from all RGB channels

-8

Max shadow recovery & exposure

As we prior stated, in order to clarify, at choice we can chose our spot metered “none recovered highlight end” to be the value immediate at clipping of all channels (RGB 255), or at start of the shoulder at defaults in Capture One. The latter was my personal choice and is basis for 2 " in above. Additionally, we can note that from about -3 to -2 stops (Graph 3) is where we capture best quality RGB values for aggressive processing. For spot metering landscapes and similar scenes my own preference is to use same spot meter as Ansel Adams used, the discontinued Pentax Digital Spot Meter. This meter display EV (Exposure Values) in a readout display in the viewfinder, and that thereafter are transferred manually to the inner wheel which feature EV values and shutter speeds, while an outer wheel feature ISO and aperture, please see Figure 3. Reading of shutter and aperture combinations are thus at a quick glance since all such are available before the eye. For my AFi-II 12 I have modified a Pentax Digital spot meter with my own personal Digital Zone Scale, which is similar to how large format photographers frequent modify such meter affixing a Zone Scale, see Figure 3.

Figure 3. (a) Modified Pentax Digital Spot Meter (discontinued), modified with (b) Personal Digital Zone Scale (suited for AFi-II 12)

Upon my personal zone scale for Pentax Spot Meter, I could of course instead apply stops above and below medium tone, which is shown in Figure 4. There, M is medium tone, and the extremes of the latitude of my particular sensor are in blue and red stops.


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Figure 4. Zone Scale in stops compared to M, medium tone exposure (red and blue values designating extremes of the latitude of sensor without and with recovery in post processing).

Figure 5. Simplified graphics of the latitude of the particular sensor in my digital back.

Figure 5 is a simplified explanation of the latitude of the sensor for my particular digital back, with the values relative medium tone that I can use to spot meter a scene for the precise decision for locating the latitude of the sensor per the scene’s dynamic range. This presumes the base ISO 50 for highest quality image values, since I find little use to apply spot metering to higher ISO scenes with this precise spot metering method.

Simplified Precise ETTR with In-Camera Spot Meter As stated in above, we can measure only one spot value for an exposure, and we can do so with the max highlight value including all RGB channels by applying as negative exposure compensation the number of stops for that high value above medium tone. However, we need to consider the larger area of measure than for a 1-degree spot meter.


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Image 8. Building across from Yu Yuan Garden in Shanghai. High contrast scene shot into direct bright backlight to point I thought image would not be useful, not so! ISO 50 1/55s f/11, hand held. Pentax Digital Spot Meter, Leaf AFi-II 12 on Rolleiflex Hy6 and Schneider AFD Xenotar 80mm f/2.8 PQS. E/S/H 0/100/80. E/S/H 0/100/80.


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APPENDIX - COMMENTS ON SOME TOOLS

I use Leaf and Capture One because I consider them as excellent tools. On basis of the preceding chapters, the following are some comments on those tools, and on two hand held meters.

Leaf AFi-II / Aptus-II

Figure 6. (a) Default histogram and exposure info, (b) optional larger histogram, ref: Leaf Aptus-II User Guide (latest GUI).

Leaf AFi-II /Aptus-II display two histograms based on RAW values. As per Photo Figure 6 the optional larger histogram is an RGB histogram, where vertical lines to either side of the histogram indicate when one channel clip and the right and left side of the graph indicate when all channels clip. A numeric value (-1.49) indicates the overall location of the histogram on basis of RGB values, but not related to the exposure. The exposure information could thus be improved by showing numeric value of the important right toe of the histogram and the maximum highlight value. The Rolleiflex Hy6 cameras are top notch state-of-the-art in medium format and receive data from the AFi backs since there is a histogram displayed in the display on the camera handle. Thus it would appear that it would be technically feasible for the cameras to be modified to include an Auto-ETTR mode based on an initial ETTR evaluation exposure.

Capture One Based on prior chapters it would appear simple for Capture One to add Zone System display of an image in incremental grey values in stops per the zone system. The use of this would be to enable ease of inspection of an image for the contrasts captured before and after adjustments in Capture One. It would of course be possible to add also a zone system tool similar to the color editor for the modification of contrasts. In principle, it would be feasible for Capture One to add an expanded RAW tool, which through combination of multiple exposures say 2-3 stops apart would combine the RAW data into one “new” RAW file with expanded dynamic range, for further “conventional” processing in Precise Digital Exposure.pdf / andersloof.com

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Precise Digital Exposure 129

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