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The Digital SLR Camera for Teaching, Learning and Digitisation

Last updated: 12 February 2008
Published in: Digitising analogue media | Creating new digital media
Tags: analogue collections | cameras | photography | slr

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Summary

Digital SLR cameras have improved dramatically over recent years, they have also become much cheaper. Consumers can now buy an entry level digital SLR for around the same price as a top of the range compact. This paper explains the difference between a digital compact and digital SLR and shows how to get the most out of this type of camera.

Introduction
What is an SLR camera?
The SLR system
Why use an SLR camera?
Getting the most from an SLR camera
Further Resources

1. Introduction

The world of digital photography has evolved dramatically over the last decade. Ten years ago the digital SLR (Single Lens Reflex) camera was a very exotic and expensive piece of equipment. The images these cameras produced were quite poor when measured against the quality of the pictures captured by today’s cameras. These cameras were also fairly specialist devices: mainly used by news and sports photographers where speed of delivery was more important than quality.

Today, top of the range digital SLRs can still command breathtaking prices but the quality and usability of these cameras have improved enormously. In addition to producing professional SLR cameras, manufacturers have recognised (and often fuelled) the demand for affordable digital SLRs.

As such, manufacturers now produce a large and rapidly evolving range of consumer and ‘prosumer’ cameras. For anyone considering buying a digital camera in today’s market there is little difference in price between a high quality ‘point and shoot’ digital compact and a consumer digital SLR.

The modern consumer digital SLR has been designed to offer the flexibility and quality required by the serious photographer as well as the ease of use preferred by the novice. Because the SLR can be put to such a wide variety of applications it has become an attractive tool for those involved in teaching and learning or digitisation projects within HE and FE.

Diagram 1. A typical digital SLR camera

A typicla digital SLR camera

2. What is an SLR camera?

The SLR camera uses a rapidly moving mirror, prism and focusing screen to allow the user to view, focus and compose a scene accurately. The scene in the viewfinder will be the same as that captured by the film/sensor.

Although most digital compacts allow the user to view the same scene as the camera will capture, they usually use a digital viewfinder rather than a direct optical system. This is prone to reflection and glare and results in poorer image quality than viewing directly through the eyepiece. The digital viewfinder also fails to offer the same level of accuracy over exposure and focus as you would achieve with an SLR camera.

Diagram 2. Cross section of a digital SLR

Cross section of a digital SLR

While a ‘point and shoot’ camera is a highly sophisticated device its operation is quite simple when compared to a digital SLR. Unlike a compact camera an exposure made with an SLR camera involves a complex set of operations and employs a large number of moving parts.

Normally light from the subject is reflected by the mirror and pentaprism to the eyepiece to assist in composition. When the shutter button is released the mirror flips up, the aperture closes down to the chosen setting, the shutter opens and the digital sensor is exposed to light.

During the exposure the light path is directed towards the sensor and away from the pentaprism and so the viewfinder blacks out briefly. At the end of the exposure, the shutter closes, the mirror drops down the aperture reopens and the camera is prepared for the next exposure.

In addition to the light path illustrated in Diagram 2, most digital SLRs direct some light away from the viewfinder and towards special sensors that are used for measuring exposure and focus. This system is quicker and far more accurate than those currently used in ‘point and shoot’ cameras and is one of the reasons why some compact cameras are still prone to ‘shutter lag’.

3. The SLR system

The digital SLR camera is the hub of the photographic system. It is easy to forget that the camera is a single component in a large modular system – the SLR system could include a variety of accessories such as: lenses; flashes; cable releases; tripods; copystands; GPS receivers; Wi-Fi transmitters; grips; and radio and infrared flash triggers.

This highly flexible system allows the user to create a custom set-up to satisfy their needs and budget. The main camera manufacturers have developed their own lens mounts. For example, the Nikon F mount has been used on over 400 lenses since it was first developed in 1959. This means that most of these lenses can be attached to a modern digital SLR.

However, it is important to recognise that some of the features offered by modern cameras, such as autofocus or exposure control, may not be available when using older lenses.

Diagram 3. SLR system accessories: 18-35mm standard zoom lens (left); 14mm wide angle lens (centre); Camera mounted flash (right)

18-35mm standard zoom lens (left); 14mm wide angle lens (centre); Camera mounted flash (right)

4. Why use an SLR camera?

Due to its complex optical system the SLR is considerably larger than the average non-SLR camera. The camera also presents the novice user with an intimidating array of buttons, dials menus and controls. With this in mind, what is the appeal of a digital SLR?

As mentioned, the SLR is a single component in a large modular camera system. The camera can accept a variety of lenses and flashes as well as many other accessories. The SLR can also be mounted on a copystand or tripod. This flexibility allows the camera to be configured to meet the requirements of the digitisation project.
Camera controls are more accessible, often in the form of dials and buttons rather than buried deep within a menu system (typical for compact cameras).
Many photographers prefer the clarity and accuracy of a direct optical viewfinder over the digital viewfinder system used by most compact digital cameras.
Digital SLRs normally have faster start up and operation and are less prone to shutter lag than the smaller cameras.
The size of the typical sensor used in a digital SLR is significantly larger than the sensors used in the average compact digital camera. An SLR with its larger sensor will normally offer greater sensitivity, less sensor noise and more control over depth of field than a point and shoot camera with a smaller sensor.
It is easier and therefore cheaper to make a large high quality lens for a digital SLR than it is to make a small high quality lens for a compact digital camera. SLR lenses normally offer larger apertures (faster) than the equivalent compact camera, and they also provide a wider choice of apertures.
If you are already familiar with an analogue SLR, a digital SLR operates in a very similar way and may even accept the same accessories.

5. Getting the most from an SLR camera

The digital SLR system supports a large range of accessories, which is ideal for the experienced photographer. However, for the novice it is possible to mistakenly select a component that is not ideally suited for the task you have in mind.

This can lead to disappointing results and have a serious impact on the quality of the images taken. So it is important that you carefully research your needs and the features offered by each item of equipment.

Here are some tips to avoid problems and improve your photographs:

5.1 Try before you buy!

Most cameras are sold with ‘cheap and cheerful’ lenses which are designed to capture the average subject. More specialist lenses can cost from £150 to £6000, though they can be hired for a fraction of the price. Some retailers will offset the cost of rental towards the full purchase price.

5.2 Familiarise yourself with the viewfinder

The viewfinder is one of the key features of an SLR camera. The viewfinder helps you to compose the scene, it provides valuable exposure data and it shows you where in the scene the camera is focussing and taking light measurements from. It may also tell you: which metering mode you are using, if the focus point is sharp, if the flash is available and how many more images can be taken.

During composition, light from the scene is reflected by a mirror and directed through a pentaprism to the eyepiece. Some light is also directed away from this path and used by the camera to calculate the exposure and to assist the auto focus system.

Because point and shoot cameras use the sensor both during composition and exposure, the light path cannot be diverted and alternative, less accurate and significantly slower methods of light metering and focussing must be used.

Most digital SLRs offer a choice of points that the camera will use to set the focus or to take light readings from. These can be seen in the centre of the viewfinder in diagram 4.

Diagram 4. SLR viewfinder

SLR viewfinder

While the viewfinder does offer the user greater clarity and accuracy over composition it is not always the ideal method for viewing a subject. If the photographer is capturing a flat object with the camera mounted on a copystand it may be difficult or even dangerous to look through the viewfinder.

Many digital SLRs can be tethered to a PC and operated remotely. The PC displays the captured image and camera settings, fine adjustments can be made to the exposure and focus or the camera can be repositioned before the final image is taken.

5.3 Start with the automatic settings

The range of settings, dials, buttons, menus, and accessories can be quite intimidating for the beginner. The novice photographer can make use of the camera without having to master every aspect of its operation by using the fully automatic exposure mode.

In this mode the SLR behaves more like a less sophisticated point and shoot camera. The camera deals with the technical aspects of exposure and focus, whilst the user can concentrate on the composition of the picture.

This ability to capture high quality images quickly without requiring an intimate understanding of the camera makes the SLR a useful tool for recording field work or classroom activities.

5.4 Explore the more advanced features

Controlling exposure
As your confidence grows, you can then experiment and make use of the scene modes or the semi automatic modes (A, S, P) or take total control over your exposure with the manual mode (M).

Diagram 5. Exposure mode dial

Exposure mode dial

White balance
A photograph of an object taken under one type of light may have a very different colour appearance to the same object photographed under a different type of light. All light sources have their own unique colour characteristics or colour temperature: flash and daylight has a blue bias; domestic or tungsten lighting has a red bias; and fluorescent generally has a green bias.

Digital cameras can normally identify and correct for this bias, a process that is known as white balancing. Most cameras offer a choice of white balance controls, allowing you to apply settings designed for specific light sources, or you can let the camera take full control with the Auto White Balance setting (AWB).

Under average conditions the AWB setting will produce satisfactory results, however the preset values usually result in improved colour accuracy when used appropriately. If the preset white balance settings are used, it is important to always check that the setting is appropriate to the available lighting conditions as an incorrect setting can result in an unwanted colour cast.

If the incorrect white balance setting is used and the image has been captured in the Raw format it is possible to apply an alternative white balance setting during the conversion process.
Using the RAW file format
While the majority of compact digital cameras only offer the JPEG file format, digital SLR cameras also offer their own unprocessed RAW format. A handful of cameras also offer TIFF files. Once you understand the conversion software and have the available time, consider capturing in the RAW format.

While JPEG files are converted from the captured data by the camera, RAW files are unprocessed and stored in their original state. The processing of the capture data is postponed until the images are opened on a PC. This offers the user greater levels of quality and control over the conversion process. The drawback for this is that it does require more work and can slow down the workflow process.

If you choose to let the camera create JPEGs or TIFFs, switch off in camera sharpening’ and ‘colour enhancements’.
Moving beyond the built-in flash
If your camera has a built in flash, avoid using it unless in very bright direct light or back–lit conditions where the flash may help to reduce harsh shadows or remove silhouettes. The built in flash is an unflattering light, which, due to its position so close to the lens axis, produces a stark ‘forensic’ illumination.

If you require flash lighting, you might consider a hand held flash unit, which can be mounted on the camera’s dedicated flash mount known as the ‘hot-shoe’ or even a full studio flash system.
Tripods and copystands
Consider getting a sturdy tripod or copy-stand to provide a stable base for your camera. A camera mounted on a sturdy tripod will be less dependent on the built in flash under low light conditions and be less prone to camera shake