Underwater Photography E-Book

Nick Robertson-Brown

• Herausgeber: Crowood
• Kategorie: Geisteswissenschaft
• Sprache: Englisch

Seitenzahl: 319

Veröffentlichungsjahr: 2014

Beschreibung

Underwater photography is a challenging discipline. To capture an underwater world of glorious colours, extraordinary creatures and mysterious depths, you must have confidence in your diving abilities and be very comfortable with your camera. This practical book explains and offers advice to the reader on both the art and the science involved in capturing stunning underwater shots. Contents include: Advice on the equipment you will need to get the most from your underwater photography; Descriptions of underwater habitats and animal behaviour; Guidance on how to be a responsible photographer; Direction and assistance on topics including composition, natural and artificial lighting, exposure and underwater conditions. Superbly illustrated with 206 stunning colour photographs.

Leseprobe

Underwater Photography

Art and Techniques

Nick Robertson-Brown

First published in 2014 byThe Crowood Press LtdRamsbury, MarlboroughWiltshire SN8 2HR

www.crowood.com

This e-book first published in 2014

© Nick Robertson-Brown 2014

All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publishers.

British Library Cataloguing-in-Publication DataA catalogue record for this book is available from the British Library.

ISBN 978 1 84797 658 1

Frontispiece

Pink anemone fish tend to be shy and rarely approach the lens. This one was taken hiding in it’s host in the Lembeh Straits, Indonesia. 1/100; f22; ISO 250. Nikon D200, lens 60mm.

Acknowledgements

I would like to thank all the people who have supported me throughout the writing of this book, in particular Nick Barrett for his tireless proof reading and painstaking attention to detail, and also Tom Tyler and Yo-Han Cha for their last-minute proof reading. I am grateful to Takuya Torri for some of the equipment images, and also to Steve Warren at INON UK for technical advice and for his kind words in the foreword. Finally and most importantly I owe a huge debt to my wife Caroline, for all the IT support she provided, as well as modelling for many of the photographs – several of the best images in the book belong to her too.

CONTENTS

Foreword

Introduction

  1    The Camera

  2    The Equipment

  3    Getting Started

  4    The Underwater Environment

  5    Natural Lighting

  6    Artificial Lighting

  7    Composition

  8    Exposure Revisited

  9    Animal Behaviour

10    Wreck Photography

11    Low Visibility

12    Habitats

13    Image Manipulation

14    The Responsible Photographer

Glossary

Index

Foreword

Each dive we make promises to be a unique experience. For many divers underwater photographs have become the best way to recall and share those experiences. For how can a few words hastily scrawled in a damp logbook evoke the wonder of the lakes, rivers, seas and oceans each of us explores? And who else would read those words anyway? Most of us have been seduced to begin our incredible journey under the water through images. Through our own underwater photographs we remind ourselves and prove to others that we were actually there.

But taking good underwater photographs can be both difficult and frustrating. Although digital underwater camera equipment, especially the compact camera, seems to promise easy results through a smorgasbord of automatic functions that do all the work for the diver, the reality is very different. Unlike photography on land, where a casual shoot from the hip approach can work surprisingly well, it is rarely successful beneath the waves. The diver wanting to take good underwater images needs to understand how their camera functions and how to control it.

The underwater world puts a myriad of subjects before our lens. And, naturally, we want to photograph all of them! From the eel lurking in the twisted companionways of a sunken liner to the looming bows of the ship itself, we are spoilt for choice. But each subject requires different equipment and a different approach. In addition, underwater photography is almost always done against the clock. Few recreational dives exceed sixty minutes and even the most enthusiastic photographer is unlikely to spend even five out of every twenty-four hours actually taking pictures. The light is poor, visibility poorer still. Some subjects are incredibly hard to find and exceptionally wary, like orcas, and some underwater environments, such as caves, require specialized diving skills to access and survive. The odds of successfully taking that defining underwater image are stacked against us, the diver, in ways few land photographers will ever confront.

In this book Nick Robertson-Brown stacks the odds of success in your favour. He explains the must-know information that divers with little if any knowledge or experience of land photography will find essential for taking underwater photographs they can be proud of. Nick’s approach is straightforward and is easily understood. The maxim ‘a picture is worth a thousand words’ is one that the best writers about photography skills embrace. So Nick gets to the point fast and breaks it down into information you can immediately apply. There is no self-serving waffle or obfuscation.

Nick’s career as a working underwater photojournalist, his accreditations from the professional photographer trade associations and the stunning portfolios of the many students he has taught as an underwater photography instructor are solid proof of his abilities. Follow the methods and advice so hard won and yet so freely given by Nick Robertson-Brown and look forward to making great underwater photographs of your own.

Steve WarrenOwner of underwater photography specialists INON-UK; organizer of the annual underwater photography festival Visions in the Sea

Porcelain crab.

These porcelain crab occupy an anemone, sharing their host with the “Nemo” fish and helping to keep it clean and parasite-free.1/00; f18; ISO 400. Nikon D700, lens 60mm.

Introduction

When William Thomson, a solicitor, first put a camera under water off the English coast of Dorset in 1856 I am sure he had no idea what he was about to start. He put the camera on the end of a pole, and in about 6m of murky water he captured a rather indistinct picture of a bridge in the Wey estuary in southern England. Twenty years later, in San Francisco, Eadweard Muybridge attempted a similar experiment. The early image taken by Thomson has sadly been lost, and it was not until 1893 that Louis Boutan went under water in a hard hat with surface-supplied air that images were actually taken while diving. These photographs were taken in the Mediterranean and this exciting work was pioneering in its day. The work of Boutan is seen by many as the start of the story of underwater photography. His book La Photographie Sous-Marine was published in 1900.

Progress in underwater photography was relatively slow for several years after this, although in 1914 John Ernst Williamson shot the first ever underwater motion picture, and in 1923 W.H. Longley and Charles Martin took the first underwater colour photographs using a magnesium powered flash. There were small improvements throughout the First World War but it was not until the 1930s that really important developments started to take place which led to the improvement in underwater photography equipment and techniques. In the 1930s, exploration of the oceans led to the need for more and better photography equipment. In addition, the invention of scuba systems made it far easier for the divers to move around without being attached to a surface-supplied air hose. The invention and development of strobes as part of an underwater lighting system led to a rise in the number of people getting involved in underwater photography.

One of the principal characters in underwater photography is Jacques-Yves Cousteau. His books and films were seen by so many people on the new medium of television that the public began to believe that they could do it too. Working with the Belgian Jean de Wouters they developed an underwater 35mm camera called the Calypso-Phot. The design was innovative and made by Atoms of France. It was bought by a Japanese photography company and then released in 1963 as the Nikonos. It had a maximum shutter speed of 1/500 of a second and became the bestselling underwater camera series ever made. In the late twentieth century, ever-improving equipment and the increasing popularity of recreational scuba diving made underwater photography accessible to both amateurs and professionals alike. There are two other notable personalities from the pioneering era of the late 1940s to the 1960s who should not be forgotten; they were Hans and Lottie Hass. Their films and dedication to the protection of the underwater environment inspired many people to take up diving and underwater photography. In 1949, Hans helped to develop the famous Rolleimarin underwater housing for a double lens reflex Rollei square format camera. It became the most successful underwater camera of its time.

Fig. 0.1

Boha snapper schooling in the Red Sea off Ras Mohammed.1/160; f16; ISO 640; Nikon D800

However, probably the most influential improvement in underwater photography occurred with the arrival of digital cameras. Even with the introduction of model-specific underwater housings for the 35mm SLRs, the diving photographer was still limited to the maximum number of shots he could get out of one roll of film. Once underwater, the photographer was committed to using whatever kind of film he or she had chosen: there was no changing of film speed, which can now be emulated in a digital camera while still underwater. The film speed or ISO is explained later on in the book, but essentially it increases or decreases the sensitivity of the film or the sensor, allowing images to be captured in darker light with a higher ISO. The screen on the back of the camera allows you instantly to review your images, and thus make any changes accordingly. In the days of film photography, many photographers would take three or four shots of the same image using different exposure settings in what was known as bracketing. Once the photographer returned to the surface, the film still needed to be developed and printed. Film has now, essentially, been replaced by a memory card. Even on the camera’s highest resolution setting, most memory cards will hold several hundred images. The digital revolution has made a huge difference to photography and the pace at which improvements are being made is staggering.

If you are a scuba diver, free diver or snorkeler and you have decided to take your camera with you, then you have taken the first step to open up a new dimension to your passion. Capturing images under water can be seriously rewarding when you can review the amazing marine life that you saw on your last dive. It can also be both frustrating and confusing, very often on the same dive. I hope this book will be able to guide you through many of the pitfalls and teach you how to overcome them in lots of small, easy steps.

To be a good underwater photographer you need to be an excellent diver. Good buoyancy is essential, and awareness of your surroundings is equally important. If your camera system is not neutrally buoyant, then your own buoyancy is going to be affected. Ideally you should balance your camera system so that it is neutrally buoyant, but many underwater photographers prefer to have their systems slightly negative. There are many issues to consider and these will be covered in depth.

If you are new to underwater photography you may need to consider changing or adapting some of the equipment that you use. For example the exhaust vents of your second stage may direct bubbles in front of the camera lens, and you may need to consider getting the regulator that is more suited to underwater photography. Your eyesight may have been perfectly acceptable for normal diving, but you will need to review your images underwater on the screen, and as the screen is small it can be very difficult to pick out detail. If your close-up eyesight is not perfect then you may want to look at purchasing a twin lens mask with gauge readers in order for you to be able to review your images.

Fig. 0.2

Orangutan crab hiding in a bubble anemone in Bunaken, Manado. These crabs really do appear to be covered in orange hair. 1/160; f5; ISO 200. Nikon D200

In photography there are numerous techniques and styles, and underwater photography is no different. You could spend a week diving in one location but the style of photography on the various dive sites of that location could be completely different. Some sites may be suitable for macro and super macro while others suit wide-angle or close-up wide-angle, and others could be reef and wreck photography. These sites are all different and require varying techniques, but there are no rules in the underwater photography world and many of the techniques are adaptable and interchangeable.

Fig. 0.3

The Giannis D wreck off Ras Mohammed in the Red Sea, taken from the classic stern position and converted to sepia to add to the atmosphere of the image. 1/100; f14; ISO 250. Nikon D800

Many underwater photographers like to specialize in one category, such as macro or wide angle. While you might want to concentrate on developing your own style and focussing on what you enjoy, it is also great fun to try to expand your repertoire. You should be encouraged to try out new techniques and generate your own style. Underwater photography is about producing images that you, personally, find appealing (unless you are looking to sell your photographs). However, to get full satisfaction from your efforts you must learn to understand the limitations of your camera and equipment and be able to review your image under water, decide what is wrong and change it there and then. If this book helps you achieve this, then it will have succeeded and so will you.

Farnes seal.

Common seals are abundant around the coast of Great Britain and Ireland. This was taken in the Farne Islands off northeast England and is so used to divers that they love to interact.1/160; f16; ISO500. Nikon D700, lens 60mm

Chapter 1

The Camera

Cameras have been around for a long time. The first cameras were believed to have produced images in 1816, and the principle of these first cameras can be seen in a simple pinhole camera with an opaque screen for the image. As the light passes through the pin hole (aperture) it is inverted and is displayed on the screen.

In the early cameras, the ‘screen’ was a photographic plate: a sheet of paper, or other material, impregnated with silver nitrate. The impregnated chemical reacts to the density of light, and this forms an impression of the image when ‘exposed’ to the light for any length of time. The image is thus ‘burned’ onto the plate as a negative and, when developed, the image can be seen as a print.

In the early part of the twentieth century Kodak took the lead in bringing photography to the people. The box Brownie camera was introduced by Kodak in the United States and Western Europe in the early 1920s and retailed for $1–3. It was capable of capturing some excellent pictures using 120 film with eight shots on a roll. It had up to three aperture settings and the expensive ones even had a limited choice of shutter speeds.

Fig. 1.1

A Denise pygmy seahorse taken in Raja Ampat in Indonesia. This seahorse was taken with a high shutter speed and high f-stop and just given a tiny bit of light from twin strobes to create the black background. This seahorse is very tiny indeed, around 2–3mm long.1/250; f16; ISO 250. Nikon D700, 60mm

Digital cameras are not that far removed from these first cameras – in principle at least. The only real change is that the film has been replaced by an electronic device that is sensitive to light; we call this the sensor. The digital sensor is, however, only part of the work flow to convert light/subject into an image. The image is carried through several stages before it appears in a usable form at the memory card. The result can normally be viewed on the screen on the reverse of the camera.

The image passes through the lens, which is in fact a series of lenses, where it is then focussed onto the sensor. The sensor is a sheet of semiconductor containing an array of millions of light-sensitive ‘mini-sensors’. The number of these light-sensitive mini-sensors accounts, in a large part, for the resolution of the picture, and because there are so many of these pixels they are measured in their millions. Many cameras are, not always correctly, judged purely on their megapixel count.

Fig. 1.2

The image of the pinhole camera in this diagram shows the rear of the box. This one is actually a camera obscura and the image would appear inverted on the screen you can see.

Fig. 1.3

This box Brownie camera dates from some time in the 1930s. This one was a limited run of red colour – most were black.

Fig. 1.4

The image shown here is just to give an example of what can be seen on the screen on the back of the camera. I took this hawksbill turtle on a night diving whilst carrying out research on turtle populations on a tiny island in the Caribbean.1/125; f13; ISO 400; Nikon D700, 16mm.

These sensors are photo-sensitive diodes that convert the light into electricity and each one is sensitive to a particular colour: red, green or blue (RGB). The coloured light from the image you are trying to capture is usually a mixture of colours. Where you believe you can see blue light, it may be made up of components of blue, green and red. These individual components of colour are detected at the corresponding sensors. Each of these sensors has a small gap between them and it is the individual sensor plus the gap that actually creates what is termed a ‘pixel’. Most modern digital cameras now have at least 12 million pixels squeezed into a space that is smaller than a postage-stamp on compact cameras. Even on a 36 mega pixel digital SLR, the sensor is approximately the size of a 35mm slide!

Fig. 1.5

The lens has been removed from this mirrorless style camera and it shows an image of a sensor where the lens should be. You cannot see the actual pixels as the sensor is behind a protective screen that is covering it.

Fig. 1.6

The simple diagram is to show how the image, once captured, passes to the buffer through to the processor, where it is then passed to the memory card.

The signal sent from each individual sensor is proportional to the amount of light and colour. From here it then enters a buffer where it is stored for a fraction of a second before being converted from an analogue signal into a digital one. The really clever stuff takes place in the processor where the binary code from the digital signal is converted into an image. This again passes through a buffer before being written onto the memory card. Similar data is displayed on the camera screen, sometimes with all the metadata. Metadata is information, embedded in the image, about how and when (and sometimes where) it was taken. Many cameras now have a GPS system built into them – not just digital SLRs but most modern compact cameras will now also have it.

CONTROLLING THE LIGHT

What can you do to create the image as you see it or want to present it? Without using artificial light, there are three factors that you, the photographer, can change. As you can see from the exposure triangle (Fig. 1.7), the three factors that affect the light/exposure on the image are aperture, shutter speed and ISO. All three have their own distinct effect upon the outcome of your image, but there are penalties involved with each method of increasing the light. The amount of light that arrives at the sensor is called the exposure value (EV). Change any one of these factors and this value will also change. Change another and you can bring the required EV back to where you wanted it. It is a question of balancing the exposure to get the right value for your situation. It is also how you balance this value that gives you, the photographer, the control of how you want to present your image. (Exposure values are explained and discussed at greater length in Chapter 8.)

Fig. 1.7

This diagram shows the exposure triangle, which itemizes the three principal components controlling how bright the image is.

Aperture

The aperture is the hole behind the lens through which light enters the camera and can be directly compared to the pupil of the human eye. In bright light, the pupil will close down to a small round opening, restricting the amount of light that falls on the retina. As it gets darker, the pupil dilates to allow more light to enter. The aperture on the camera’s lens can be opened and closed, like the pupil in the eye. The difference in the amount of light that it allows through to the sensor between being fully open and its minimum setting is extensive.

Aperture Setting

The aperture setting is referred to as the f-stop or f-number. The size of the hole is determined by a circle of blades that cause the central aperture to open and close by the overlapping of the blades on each other. This restricts or controls the amount of light hitting the sensor. The size of the aperture is given a number; these numbers are not just random figures but are, in fact, a ratio of the focal length of the lens to the physical size of the aperture. One of the issues that sometimes confuses many budding photographers is that a wider aperture giving more light has a small f-number, while a narrow aperture allowing a low level of light is a high number. Try and give yourself a simple mnemonic, for example – the higher the sun the higher the number aperture.

Fig. 1.8

The aperture is completely open at its highest f-stop number, and the amount of light that can enter the aperture is halved at each f-stop number.

All camera lenses are calibrated on the same f-stop scale. The range of the aperture numbers varies from one lens to another but the scale is constant. The f-stop index is shown in the diagram, but a lens which had the whole range of the f-stop options would probably be very expensive. Because the ratio of the aperture size to the focal length of the lens gives us the numbers in the f-stop scale, each increase in f-stop number equates to half the amount of light arriving at the sensor, for example, f5.6–8, f11–16.

Depth of Field

Opening and closing the aperture (decreasing and increasing the f-stop) would appear to be a simple way of changing the light level on the sensor. However, as the aperture is opened (reduced f-number), the depth of field reduces, and this has a very noticeable effect upon the image. So what does this mean? The depth of field (DOF) is defined as the amount of the image which appears to be acceptably in-focus.

You may think it strange that you would deliberately have large areas of your image out of focus, but some of the most impressive underwater images, especially macro, are taken with a very small DOF. The idea is to make sure that the centre-piece of your image is razor sharp and that everything in front and behind moves out of focus. We call this out of focus area ‘bokeh’. This technique is used a lot in underwater photography as you can virtually eliminate a messy background by using a low f-stop number to create a small depth of field – ideal for when your subject will not come out into the open. Nudibranchs are one example of a subject that will look great when taken head-on with a low f-stop.

Lens Choice

Another consideration for varying the depth of field is the choice of lens. For those using a fixed lens compact, this is not possible, although zooming in and out or using housing-mounted wet-lenses and dioptres (discussed in Chapter 2) can achieve a similar result. However, for the SLR and mirrorless camera users, lens choice and depth of field are a dual consideration.

Fig. 1.9

This beautifully coloured purple nudibranch is of the family Chromodorididae and is called Risbecia tryoni. It was taken in the Philippines with the lens only inches from the subject. A +4 dioptre allowed me to get really close to the subject. It was taken close to the surface using natural light.1/320; f4.5; ISO 200. Nikon D700, 105mm

Fig. 1.10

Longnose hawkfish taken on coral in the Gulf of Aqaba just off Dahab in Egypt. It was taken at around 18m or so; the dark blue background is a true representation the colour at that time.1/125; f5; ISO 400. Nikon D700, 105mm

A lens with a small focal length, such as a wide-angle lens, has a much greater depth of field at any given f-stop setting than a corresponding lens with a large focal length. For example, for the SLR users, a 28mm is a wide-angle lens and the depth of field is greater at a given f-stop than it is on a macro lens that magnifies the subject, such as a 105mm. As you move closer to the subject, the depth of field decreases. The effect is comparable with a compact camera between the widest angle (with no zooming) and the macro, or close-up, when you have zoomed in. The depth of field on the compact will be greater without being zoomed in. This is an important consideration when taking really close-up macro images, and for those super-macro shots.

Fig. 1.11

Flamboyant cuttlefish taken in Dumaguete in the Philippines. This is taking the use of close-up bokeh to the limits by getting on the same level as the cuttlefish, using a +4 dioptre on the front of the port and setting a very low f-stop. 1/200; f5.6; ISO 500. Nikon D700, 105mm

Many SLR housings have an external thread on the port or other means of accepting external dioptres. All these dioptres work like reading glasses – they allow you to get closer to the subject and magnify the image. The penalty is that the depth of field is further decreased and the camera can only focus on subjects that are very, very close. Using an external dioptre means that you can remove them to take shots other than really close-up macro. If you were to put the +4 dioptre, for example, on the camera lens and then place it in the housing, the choice of subjects is limited to those you can get really close to. As long as you do not get too upset when you miss the shot of an eagle ray as it passes you a few metres away, the results can be very rewarding.

Shutter Speed

The shutter is a mechanical device that acts as a window blind, blocking the light from the sensor when not activated, but opening for a period of time to allow light onto the sensor when the release button is pressed. This means that we can control the amount of light that falls on the sensor. The faster you set the shutter speed, the less time the shutter will be open, and therefore the less light there is coming onto the sensor.

Of course the aperture restricts the amount of light entering the camera too, but as we have discussed, the more light we allow through the aperture, the smaller the depth of field. This means there is a balance or a trade-off in how we allow light onto the sensor. When you are photographing moving objects – like fish – the shutter speed becomes the dominant factor in deciding the level of light. If you do not use a fast-enough shutter speed when photographing a moving subject, it will look blurred and out of focus. This is called motion blur and it can be used to great effect if you get it right, as it will give the impression of speed and motion like a great racing car image. These effects will be achieved if you use a shutter speed in the region of 1/30th of a second to 1/60th of a second.

However, many compact and mirrorless cameras do not have a mechanical shutter – it is all done electronically. (Mirrorless cameras are discussed and explained in Chapter 2.) When the release button is pressed, the pixels in the sensor, which are already ‘charged’ with light, start reading it and then pass the digital image through to the sensor. It is now the case with many of the latest mirrorless cameras that the image is being captured before you operate the release button and the processor is storing this, and in some cases it can actually be accessed and used. This is not possible with a digital SLR as the mirror and shutter are shielding the sensor from any light, and it is the action of pressing the release button that stimulates the processor into receiving the signals from the sensors.

Fig. 1.12

Using a slow shutter speed to create the blurry effect of rotation, this image was taken on a model shoot in a pool, with the model spinning horizontally as he moved towards me. 1/20; f11; ISO 400. Nikon D800, 24mm

Fig. 1.13

Using a shutter speed of 1/100th of a second; the crab’s mouth during eating would look blurry if the motion had not been frozen by the use of strobes. 1/100; f10; ISO 250. Nikon D200, 60mm

In underwater photography the shutter speed is also important for defining the background colour of the water, particularly if you are using flash. This is because if you are using a strobe, the shutter speed is not primarily defining the amount of light entering the camera, as it is the flash that freezes the action. The aperture should be set to expose for the subject when the flash fires. The shutter speed can be adjusted, within a small range of about 1/60th to 1/250th second, so that the background will lighten as you increase the time you leave the shutter open. If you are using natural light, decreasing the shutter speed will increase the exposure on your subject too. The interplay of aperture and shutter speed will give you a light value that will vary in a similar way to how it does in air. It is when you introduce artificial lights – powerful strobes or video lights – that the options become greater.

Shutter Speed Settings

Like the f-number scale, the options for setting the shutter speed are defined. The increments used are those that will balance the light value, that is, if you open the aperture by one stop, then increasing the shutter speed by one increment will balance the light value to what it was before.

In the menu of many of the latest cameras there is a shutter setting called front curtain or rear curtain. Most SLR and mirrorless cameras will have this facility. This mode is for use when you are shooting with flash. In front curtain, the flash fires as soon as the shutter release is pressed; in rear curtain, the flash fires at the end of the shutter action. For most underwater work, rear curtain is usually advised. This means that the flash fires at the end of your exposure, so if you have slow shutter speed and the subject is coming towards you then you can allow plenty of exposure on the background and put flash on the subject as it gets closer to you.

ISO

The photographer needs a measure of how sensitive the film is to light, and so film speeds came about. The term ISO refers to the International Standards Organization, which originally prescribed measures for photographic film, and these are still used today. Film speed came in ISO 100, 200, 400, 800 and so on, getting considerably more expensive as the numbers became higher and the film more sensitive to light. With no prior knowledge, you would assume that the higher numbers would always be the best to work with, but there is a penalty. As the film becomes more sensitive to light, the resultant image becomes increasingly grainy in appearance.

Fig. 1.14a and 1.14b

The image of the wreck as it was taken using a low ISO, so the image is relatively noiseless. Fig. 1.14b has had noise artificially induced in Photoshop and reflects how the image would have looked had it been taken at a much higher ISO. The noise in the second image is clearly visible as lots of coloured dots that should not be there.1/80; f8; ISO 200. Nikon D200, Tokina 10–17mm at 10mm

EXAMINING NOISE

You can actually test the limits of your camera for yourself by taking two photographs, one that is at your camera’s lowest ISO setting and one that is at the highest. Focus on something black, in low-light conditions, and then zoom in on your results. The low ISO image should look clean and black, whereas the high ISO image will look really noisy with hundreds of tiny, unwanted spots.

In digital imagery, the same standard has been adopted. If you were to compare a film camera using ISO 100 film to a digital camera using ISO 100, then both cameras should produce the same exposure value. High ISO is obviously a tool that can be exploited under water as high ISOs are designed to work in low-light conditions. However, as with film, the higher the ISO, then the lower the resolution and quality of the resultant image. The picture becomes noisy, giving an effect much like the grain of film – noise can be described simply as an unwanted by-product of image capture that adds extraneous information, often seen as tiny red dots.

If you have your settings in auto, the camera will select the appropriate ISO settings according to the light conditions. Under water it is normally dark and so most images taken under water in auto will be noisy due to the camera selecting a high ISO. Many novices complain that their images are not sharp and look fuzzy. This normally occurs because they have had their camera set to auto. This is one of the main reasons for the fuzzy noisy images and why you should not use the auto mode under water. High ISO can work in some compositions when noise may enhance the image. This is unusual but it does occasionally work, normally for a wreck or cavern imagery.

Metering for Light

Most digital cameras will offer a choice of methods for metering the light coming into the sensor.

Average

In this setting the camera will measure the overall exposure of what is on your screen or viewfinder. This is a good default setting which will tend to give the best results on an evenly lit scene.

Centre Weighted

While this system will work similarly to the average metering mode, it will place more emphasis on the central area of the frame, and is useful when it is either dark or light around the edges of the frame.

Spot Metering

This measures the light in the centre of your frame and is particularly useful when shooting at silhouettes, as it exposes for the dark subject and not the light behind. This will allow you to use the light and not lose it.

Exposure Compensation (+/-)

Most digital cameras, of any format, will have an exposure compensation (+/-) button. In the automatic mode, the camera will look at the overall intensity of light in the frame and meter the f-stop, shutter speed and ISO accordingly. You can affect the way the camera meters light by choosing a more suitable meter mode (see below), which works well in most situations, but the camera will still select the exposure for a midpoint between the lightest and darkest parts of the area that you have selected in the metering mode. If you are photographing a dark subject on a light background such as sand, or a light subject such as a silvery fish against a dark reef, then this can confuse the camera’s light metering system. This will cause the subject to be predominantly exposed, either for the sand or the reef, and thus will be under or over exposed respectively.

By selecting a higher or lower setting on the +/- you can compensate for this. For bright scenes, you need to select a positive number (+1/3, +2 and so on) and for the dark scenes, move it to a negative number. This confuses some people – increasing the exposure for a bright scene? Remember, the camera has metered for a bright scene so the camera will lower the amount of light hitting the sensor and your dark subject will be underexposed. Conversely, if the background is dark and your subject, say a shiny fish, is light then the average light your camera will see is low and it will allow more light through the sensor, overexposing the subject. This facility can also be used in manual mode; if you are using the camera’s inbuilt light meter, which many cameras have, then it will be telling you the same thing. A dark background with a light subject will average the light in the scene and overexpose the subject. In this case, you will need to either reduce your exposure settings or choose a negative number on the +/- facility.

Fig. 1.15

These five images were all taken at the same time, but the exposure compensation button (+/-) was selected to: -2; -1; zero; +1; +2.

In the days before the digital revolution, photographers using film would ‘bracket’ their shots, setting the exposure one and two stops above and below the light meter reading, giving five shots of the same subject in all. You can do this yourself in several ways. You could shoot the same shot five times, at EV -2, EV -1, EV 0, EV +1, EV +2. An alternative way would be to adjust the ISO, shutter speed or f-stop one and two stops up and one and two stops down, but this is quite long winded. The simplest way to do this would be to use the auto exposure bracketing if your camera has this particular mode, and it will do this for you, producing several images either side of your selected exposure.

FOCUSING OPTIONS