www.realworldimages.co.uk

Photography and Art

Feature: Profile of the Compact Camera

Introduction

The compact digital camera represents the most convenient and popular form of camera with consumers. Its small size makes it very convenient to carry at any time of the day. Their feature set are continually increasing to build on their versatility to keep up with modern demands. Technology originally seen in DSLRs are slowly being passed down to the compact camera in amended form.

Key Characteristics of the Digital Compact:

  • Light Weight
  • Small imaging sensor
  • Large LCD monitor
  • Optically slow zoom lens
  • JPEG image recording format
  • Pre-programmed scene modes
  • Image stabilisation
  • Low powered flash
  • Video recording capability
  • Built in memory capacity

Imaging Sensor

The sensors used in just about all compact cameras is considerably smaller than that used in the DSLRs. Measuring around 4x3mm to around 7x5mm their small size help to ensure that the lens elements are kept as compact as possible. With each generation of camera the number of pixels used to form a sensor is currently still on the increase. The very latest compacts now feature 14 megapixels (MP) which is the equal of some D-SLRs. Increasing the pixel population should in theory increase the amount of captured detailed but they are so densely packed that they struggle to capture sufficient light.

Image Noise

The reduction in pixel size has meant that each pixel as a result collects less light than before. The image produced by the sensor at its base (lowest) ISO setting (say ISO 100) may look clear and clean but as the ISO is increased (image gain is boosted) noise becomes a factor. To counteract this issue some form of noise reduction is employed. With  small levels of noise, noise reduction can work extremely well and allow the camera to produce quality images at increased ISO. However, if the image noise level is too high, the noise reduction system must work harder and this usually results in images with reduced detail and strange artifacts.

Despite the limitations of the sensors used in compact cameras, manufacturers are now providing even higher ISO settings. At one time ISO 800 was about the limit but now some cameras have ISO settings up to ISO 6400 (more about this later).

The auto ISO range provided on many cameras usually represent the more useable range before image noise becomes too intrusive.

Exposure Control

The control of a camera's exposure control in terms of aperture and shutter controls is use usually limited as this function tends to be fully automated to follow a predefined program. The camera will react solely to its internal program and the immediate lighting conditions. Luckily, the exposure can be tailored to some extent by the provision of an exposure compensation feature. This feature makes it possible to lighten or darken an image but it won't give effective control of aperture or shutter speeds.

An alternative method to help achieve the correct image exposure is to use the correct type of metering. This feature is no longer seen as a high end feature and can be found even on budget compacts. The standard metering method is to meter the area in focus supported with added metering information from around the scene. This is often referred to a evaluative metering and on the whole it works very well for most lighting conditions. An alternative method is the use the old style centre weighted metering whereby most of the metering information is biased towards the centre of the scene. This method give accurate results as long as the way the meter is measuring light is understood. The final type of meter is used mainly for tricky lighting conditions. Spot metering just looks a small percentage of a scene (typically 3%). Care must be used when employing this metering method as it can easily lead to under or over exposure of the scene you are trying to capture.

Programme Modes

As most of the compact cameras are designed for anyone to use, most will feature predefined programme modes. The basic modes of portrait, action, landscape and macro have been extended considerably on many models to include fireworks, party, child, food and many other conceivable shooting situations. It's just a matter of looking at what you wish to shoot and selecting the required programme mode.

Autofocus

All compact digital cameras are using a method of autofocus called contrast detection. Rather than having a separate autofocus module as required by DSLRs, autofocusing is based on information gained from the sensor. The cameras lens is adjusted until the cameras processor determines that correct focus has been achieved. The process is usually slower than that in a DSLR but as the technology improves so does the achievable AF speed. One major benefit of contrast based focusing is that focus is not just restricted to one particular area but if implemented autofocus can be achieved from any location on the sensor. This type of flexible AF implementation can be found in some high end cameras but for most compacts the focus areas are predefined.

A focus aid light source, usually a red or orange in colour, is provided to assist autofocusing in low ambient light levels.

A more recent innovation is Face Detection based AF. The face detection technology employs special algorithms that identifies human facial features from a scene. The face can be detected be it facing towards the camera, at an angle or in profile. Several faces can be detected at a time with one face prioritised for focus and exposure determination. Even if the subject is off-centre and the background is bright, face detection will ensure that the subjects face will be focused on an the exposure adjusted accordingly.

Image Stabilisation

The light weight of compact cameras make them comfortable to carry around but has the disadvantage of making the cameras more susceptible to camera shake. As a result it is essential when shooting in low light that you grip the camera properly and find something to brace yourself against. The fact that most digital compact cameras are used away from the body due to the user using the LCD monitor to view focusing means it is more difficult to keep the camera steady.

Some manufacturers are including image stabilisation in camera ranges as a standard feature while others treat it as a high end feature. This technology comes in two flavours; optical and sensor shift. The former system makes use of a moveable arrangement of lenses that try to compensate the camera movement. The latter system shifts the imaging sensor along its axis in order to get a stable image. Both systems work well and should provide at least 2 stops of stabilisation.

An alternative method used in some cameras it to adjust the shutter speed and ISO. This method will stabilise an image but usually at the expense of overall image quality.

Flash

The flash is always a useful tool to have to add illumination when light levels are getting low. Compared to the units found on large cameras like the DSLRs, the flash units are quite underpowered and are dependant on adjusting the ISO sensitivity to provide significant flash coverage. They are at their best when the subject is close and are no doubt designed with taking people photos in mind rather than interiors of buildings. They can provide decent fill-in flash light when taking photos in bright sunlight to achieve a better lighting balance.

Flash illumination range can be as short as just 3 to 4 meters with anything above that requiring a boosting of the ISO sensitivity. With this in mind, if image quality needs to be maintained then the ISO sensitivity should be set to as low a level as possible and Auto ISO avoided.

Red eye is always always an issue with compact cameras and it is not easily avoided with the flash being so close to the lens. Anti red eye features can help with the pre-flashes produce (which close down the eyes iris) but they can lead a subject to have their eyes closed (or semi closed) by the time the actual exposure is made. An additional method now employed on some cameras is to remove the red eye in image processing start after the exposure is made.

With the flash being synchronised to work at a relatively fast shutter speed, when taking flash shots in low ambient lighting, the background will be reproduced too dark behind the main subject. A common feature which is often referred to as slow sych flash will permit background scenes to look brighter but care has to be taken to avoid camera shake. The shutter speed is reduced to allow a balance between the flash and the ambient light and so it is important to avoid any camera or subject movement during the cause of the exposure.

LCD Monitor

The optical viewfinder is becoming increasingly scarce on the digital compact camera. This is not totally surprising as the viewfinder was not very accurate and would only provide an average of around 80% view of the recorded scene. At best they were a useful for saving battery power when the battery strength was running low by switching off the LCD monitor. With increasing battery capacities and more efficient electronics battery power is no more such an issue as it was some years ago.

The LCD monitor has been increasing in size and resolution with almost each generation to the point that images are rendered in very high quality. The LCD monitor allows a range of status information to be clearly displayed along with the scene being viewed. Viewing in direct sunlight can be problematic and some cameras try to counteract this by providing controls to vary the brightness of the monitor. Sometimes this feature is provided automatically but it must be understood that this will have an impact on the battery life.

The LCD monitor can make it obvious when their are exposure or colour balance issues if the camera provides sufficient manual controls to the user.

In terms of image playback, with the large screens and high resolution, checking images for sharpness is made much easier especially with significant magnification provided. Reviewing images is more easy on the eyes and with the improved LCD technology the usable angle of view has improved so several people can view the screen at various angles.

 

Mini News

22 November 2012: Sigma 18-250mm now available in Sony's A-Mount

Sigma Imaging UK Ltd has announced that the 18-250mm f3.5-6.3 DC Macro HSM lens is now available at a suggested retail price of £499.99. Sigma's APO Macro 180mm F2.8 EX DG OS HSM lens will shortly be available in Sony's A-Mount for a suggested retail price of £1499.99.

-------

17 October 2012: Firmware update for Sony NEX 7 v1.01

Sony NEX firmware update provides the following;

  • Addition of capability to enable or disable the MOVIE button
  • Addition of exposure settings of bracket shooting (three frames /1.0EV,2.0EV, 3.0EV)
  • Improvement of response for showing auto review image.
  • Improvement of image quality when using a wide angle lens
  • Improvement of indication when setting “Flexible Spot”.

Visit the link: http://www.sony.co.uk/support/en/product/NEX-7/updates

Firmware updates are also available for the a77, a65, and a57.

-------

15 October 2012: Purchase Sigma's 10-20mm f/4-5.6 EX DC HSM ultra wide angle lens and claim FREE 77mm UV DG filter

From Monday 15th October 2012, Sigma Imaging UK Ltd are introducing a short term special offer that enables anyone who purchases Sigma’s multi-award winning 10-20mm f/4-5.6 EX DC HSM ultra-wide angle lens to claim a FREE Sigma 77mm UV DG filter worth over £60!

A Sigma Ultra Violet filter is the perfect accessory to protect your lens from damage to the front element. Sigma’s DG filters benefit from a special multi-layer lens coating, developed to counteract the highly reflective characteristic of image sensors.

Terms and Conditions apply. Visit www.sigma-imaging-uk.com or ask your local photographic retailer for more details of this offer and how to claim your FREE Sigma 77mm UV DG filter.