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Audience: Underwater photographers and students on diving courses.
Scuba Diving Magazine
Praise for the previous edition:
"In its third edition, The Underwater Photographer has evolved to become almost a standard work of reference. Martin Edge has developed his writing skills over the years, and we recommend this volume for anyone pursuing the now-less-than black art of underwater photography, especially with digital image-gathering in mind."—DIVE MAGAZINE PUBLICATION OF THE YEAR
"..let us just say that this is THE best underwater photo technique book on the market... PERIOD!"—DIVER magazine
Since the last edition was released in 2005 I have spent most of my time teaching underwater photography both in the UK and overseas. It may sound clichéd but I do learn more than I impart and one topic that is often misunderstood by the majority of beginners is the basic photographic essentials.
In previous editions of this book I offered only a limited discussion concerning these basics. Therefore I have devoted Chapter 1 to a thorough 'brush up' on the basics of photography and other digital principles. I would encourage you to bookmark this chapter as a sort of 'advanced glossary' should you fail to grasp some of these concepts in later chapters. These topics are discussed frequently throughout the book but will relate to tips and techniques specific to underwater photography.
Many underwater photo enthusiasts are eager to progress from the Auto/ Program mode on their cameras but don't have the confidence to carry it through when they get underwater. Those who are unfamiliar with the basics may find it restrictive because:
It takes control of the camera away from the user.
You can never begin to understand and appreciate why good shots turned out well and why less favourite shots were disappointing.
Throughout this book I intend to discuss and explain in detail, the merits and dare I use the word 'technicalities' of using Manual exposure as well as Aperture priority and Shutter priority underwater. To do this we need to revisit the basics of apertures, shutter speeds and ISO settings. I'm aware that some experienced photographers are still confused by f numbers, stops and speeds, so if you feel that you can benefit from a refresher then please read on.
Camera Exposure Modes All SLR cameras and the majority of advanced compacts feature the following modes:
Auto/Program, which works out all aspects of the exposure for you.
Aperture priority, in which you set the aperture (f number) and the camera automatically works out the appropriate shutter speed.
Shutter priority, in which you set the shutter speed and the camera automatically works out the appropriate aperture.
Manual exposure, in which you set both the shutter speed and the aperture.
Many cameras have additional 'auto' modes which depict icons in the form of a landscape, portrait, sports/action, close up, night, etc.
Light and Time
The two fundamentals of taking a photograph are light and time.
Light comes in via the lens and strikes the sensor, and
Time determines how long the light strikes the sensor for.
If you get these two aspects correct then you achieve an accurate exposure. If you have too little light or not enough time then you get a dark picture which is considered 'underexposed'. Too much light or too much time results in a picture which is too bright or overexposed.
The Time element is controlled by the Shutter Speed selected and the amount of time the shutter mechanism remains open for. The Light element is controlled by the size (diameter) of the Aperture.
The size of the aperture, iris, hole (it's referred to in different ways) which light passes through to reach the sensor can be controlled by you to allow more or less light into the camera. The aperture is measured in f numbers (often referred to as a 'stop' or 'stops'). The largest holes have small (low) numbers like f2.8 and f4 and the small holes have bigger (higher) numbers like f22, f16.
The full list of f numbers is as follows:
f1.4, f2, f2.8, f4, f5.6, f8, f11, f16, f22, f32, f45, f64. Where this sequence starts or finishes depends on the lens in use.
So, what do all these f numbers mean and where do they come from?
Aperture is regulated in a 2:1 ratio so that each f number represents a doubling or halving of the size of the hole and therefore the amount of light which is allowed to pass though and onto the sensor. For example, f8 provides a hole which is twice the size of f11 and the f11 hole is twice the size of f16, which means that twice as much light passes through the aperture at f11 than it does at f16. Conversely, f8 receives half as much light as f5.6.
Remember, big numbers like f22 have a small hole; low numbers like f4 have a large hole.
The origin of f numbers is simply a calculation whereby the focal length of the lens is divided by the diameter of the aperture.
Note about compact cameras
Digital compacts have an aperture control of some kind, but because compacts are physically smaller in size they tend to have smaller sensors and shorter focal lenses than the typical SLR. Because of this, the calculation is smaller. For example, on most compacts an aperture of f4 will provide similar characteristics as f8 on an SLR.
Understanding Shutter Speeds
The time element and the second way to control the amount of light entering the camera is to regulate the length of time the aperture remains open. This is done by controlling the shutter speed of the camera. When you press the shutter button, two curtains inside the camera body, just infront of the sensor, slide apart to open the shutter. After the proper exposure time the curtains slide shut to close the shutter.
The amount of time the shutter stays open is measured in fractions of seconds and on certain occassions in full seconds.
The longer the shutter is open for, the longer the exposure and more light enters the camera.
The less time the shutter is open for, the less amount of light enters the camera.
Each shutter speed is twice as fast as the previous speed.
Alternating from 1/30th sec to 1/60th sec halves the amount of time the shutter is open.
Decreasing the shutter from 1/125th to 1/60th second doubles the amount of time the shutter is open.
Shutter speeds range from 1/8000th sec, 1/4000th sec, 1/2000th sec, 1/1000th sec, 1/500th sec, 1/250th sec, 1/125th, 1/60th sec, 1/30th sec, 1/15th sec, 1/8th sec, 1/4 sec, 1/2 sec, 1, 2, 4 seconds, 8 seconds, 15 seconds and finally, 30 seconds.
Shutter speeds above 1/500th sec allow very little time to expose the photograph and are rarely used in underwater photography. Typically, 1/500th sec and above are left for topside action like sports photography, however there are always exceptions to this general rule.
Shutter speeds in the range between 1/30th sec and 1/250th sec are considered the norm, but undewater there are many exceptions to this rule in that gravity is substantially reduced, which means we can hand hold a camera at shutter speeds much slower than we would choose to on land. Experienced photographers, including myself, regularly shoot both macro and wide angle photographs at 1/15th sec — but more about this later in the book.
When a flashgun is used on a camera (whether built-in or external) there is a shutter speed which must not be exceeded in order that the flash and the camera can synchronise with each other. Most SLRs have a sync speed of 1/250th sec and 1/320th sec. For compact cameras refer to the instruction manual as they can often differ.
How Aperture and Shutter Speed Work Together
In photography, the term Exposure Value (EV) is commonly referred to as a move, either up or down, of one 'stop'. The difference between each aperture setting is one stop or one EV, i.e. f8 and f11 is a difference of one 'stop' or one EV. The difference in shutter speed between 1/125th sec and 1/250th sec is one stop/one EV. You will see that both f numbers and shutter speeds are sequenced in a series of 2:1 ratios, and this is where the two work in harmony with each other. A setting of f8, at 1/60th sec, lets the same amount of light into the camera as a setting of f5.6 at 1/125th sec, and f4 at 1/250th sec, and so on. You will see that the latter is one f-stop lower and one shutter speed higher than the former.
These combinations of aperture and shutter will all provide an identical exposure.
Understanding Depth of Field
Changing the aperture number of a camera does two things:
It controls the amount of light entering the camera.
It determines the amount of Depth of Field (D of F) in the picture.
Although a lens can focus at only one distance, the decrease in sharpness is gradual both in front of and behind the focused distance, so that within the D of F, the un-sharpness is unnoticeable. This distance is approximatley one-third in front of the point of sharpest focus and two-thirds behind the point of sharpest focus.
For some pictures, such as underwater wide angles, a large D of F is appropriate, while for others opportunities, such as fish portraits, a small D of F may be more effective.
Small apertures like f22 provide the greatest D of F, while a large aperture such as f2.8 provides the narrowest D of F.
Compare the difference in D of F between Fig. 1.13 and Fig. 1.14.
The shorter the distance between the lens and the subject the smaller the depth of field. Whilst the greater the distance between lens and subject, the greater the depth of field.
If you want a large D of F with both foreground and background in focus, use a small aperture such as f11, f16, f22.
If you want a narrow D of F with only a shallow focus, use a large aperture such as f2.8, f4 or f5.6.
After a little practice you will develop a feel for the effect for both sharp and out-of-focus portions of your photograph.
At times it can be impossible to achieve the desired aperture or shutter speed to take a photograph. This usually occurs in low light situations where you need to use a large aperture, but, because it's getting dark, you have no other choice than to use a slow shutter speed. This shutter speed required may well be too long to hand hold the camera without causing camera shake and fuzzy pictures.
In these situations this is where the sensitivity of your camera sensor comes into play by controlling ISO. Even though digital cameras do not use film, the industry has retained the expression ISO (International Standards Organisation). ISO refers to the light sensitivity of a camera's image sensor. Lower numbers like ISO 100 are less light sensitive and produce better quality images because 'digital noise' is kept to a minimum. Higher numbers such as 1600 ISO, whilst more sensitive to light, can suffer from increased digital noise.
Digital cameras allow you to adjust the image sensor's sensitivity by dialing in different ISO settings. This can be done between shots and for this reason a digital camera can rapidly adapt to changing light conditions.
The practical use of ISO is this:
If you use a low ISO setting you need more light in your photograph, which is controlled by your aperture, shutter speed or both.
A low ISO setting results in better quality.
If you use a higher ISO setting you will not need as much light in your photograph but you do risk a degredation in quality caused by 'digital noise'.
Cameras have an ISO range from 100 to 1600 and several pro camera models go up to 6400 and higher! In a perfect world it's best to shoot at the lowest ISO, such as 100 or 200, but this is not always possible.
Digital Noise — Types and Cause
A simple explanation is to liken 'digital noise' to the 'hiss' of a musical sound system when you turn it up too loudly. Adjusting volume is an amplification of the signal. When you turn up the ISO number on your camera you amplify/ increase the electricity flowing through the circuitry of the camera sensor. As the ISO value is increased, so too is the flow of electricity and the more electricity which flows through the circuitry the more interference we get, which results in more digital noise.
Digital noise is made up of two parts. One is luminance noise and the other is chroma or colour noise. Luminance noise has an effect on the grain structure of the pixels whilst colour noise appears as minute speckles of colour which are always more noticable in the shadow areas of a photograph.
For further reading go to: http://www.cambridgeincolour.com/tutorials/ noise2.htm
Another factor which compounds the problem is the length of exposure. The longer the camera takes in making the exposure, the more likely the sensor is to pick up background noise. (Be aware that using in-camera noise reduction features will increase processing time. It can take as long as the initial exposure for the camera to process the file.)
Noise tends to appear in the darker parts of a photograph and shows up as tiny speckles of colour. Cameras with full frame sensors suffer less noise because their photo sites (pixels) are spread further apart from each other and are less likely to pick up background interference. Compact cameras are particularly susceptible to noise because their sensors are much smaller. The key is to use the lowest possible ISO setting which your camera will allow as this produces the least amount of 'digital noise'.
Many camera models have a facility within the menu to activate noise reduction programs at sensitivities of 800 ISO and higher. Another popular solution is to use a noise reduction filter in your image processing workflow.
Picture Codes 'Noise Ninja' www.picturecode.com is a firm favourite, receiving excellent reviews.
For noise reviews of your own model of camera go to www.dpreview.com
Understanding White Balance and Colour Temperature
We have all taken photographs where the colours of the scene are totally false. You download it onto the computer and it has a garish colour cast. The reasons behind this will be connected to the white balance function on your digital camera.
All light has a specific colour associated to it, which is measured in degrees Kelvin (K). Take for example sunlight. Throughout the day the colour temperature of sunlight differs because of its position in the sky and the surrounding atmospheric conditions. During early morning and late in the evening the sunlight takes on a warm golden hue. Photographers refer to these times of the day as 'magic hours'.
However, around 12 noon the light is very blue and has a high colour temperature of around 8000°K. Warm colours at sunrise have a low colour temperature of around 1600° to 3200°K.
Whilst our eyes may recognise changes in colour at sunrise and sunset, for most of the day our brain compensates and we fail to notice the colour of light. This is the purpose of White Balance. A digital camera has to take into account the colour temperature of a light source and we must remember that this is both indoors as well as out in the open air.
Not only can we use White Balance to achieve a natural result, we can use also use WB to warm up or cool down an underwater photograph without it looking unnatural.
The Colour White
The aim of White Balance is to ensure that a subject, which is white in reality, is reproduced as white in a photograph, not a shade of red or green. The colour white is made up of equal amounts of RGB — red, green and blue — which are the primary colours of light. In theory, once a camera knows what the colour white should look like for a particular scene it can then produce natural colours for everything else.
White Balance Settings
Auto: Also known as AWB is perhaps the most popular setting as it uses thousands of algorithms programmed into your camera to best work out the white balance for your particular photograph wherever you may be. Auto setting as been developed over the years.
Daylight: Has a symbol of the sun and is close to the colour temperature of traditional film; many of you will remember the 'Daylight' stamp on a box of film. Daylight has a colour temperature between 5000°—5600°K and is ideal for natural light and clear skies (on land not underwater).
Cloudy: Has a symbol of a cloud and a colour temperature of between 6000°—6500°K. It has the effect of warming up the colours.
Shade: Has a symbol of a house in shade; it is an increase of Cloudy WB setting. It has a similar warm-up effect but more accentuated than Cloudy.
Tungsten: Has a symbol of a light bulb denoting use indoors under domestic lighting conditions.
Fluorescent: Has a symbol of a fluorescent light and can result in a yellow or green cast. Try it indoors under fluorescent lighting but do remember to change it back to Auto when you have finished shooting.
Flash: Has a symbol of a bolt of lightning and the results are very similar to the Daylight setting.
Excerpted from The Underwater Photographer by Martin Edge Copyright © 2010 by Martin Edge. Excerpted by permission of Focal Press. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.
Posted April 18, 2010
Since I read the third edition of this book six times, I bought the fourth with some reservations, thinking only a little would be new. I was dead wrong! The book has been entirely re-written and is -- once again to Martin Edge's credit -- simply the best book I have ever read on my passion, underwater photography. So if you've liked the third edition, get the fourth. You'll love it.
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