June 15, 2006
Aperture
Digital photographs are the result of light hitting the image sensor. Too much light and the photograph will be washed out. Too little light and the photograph will be too dark. The shutter determines how much light enters the camera, and there are two settings which are related to the shutter -- aperture and shutter speed.
Each f-number allows twice as much light to enter the camera as the previous f-number. For example, f/8 produces an exposure which is twice as bright as f/16.
Aperture settings have two basic effects -- the amount of light which strikes the image sensor, and the 'depth of field'. Depth of field refers to the length of the image which is in focus. Large aperture settings have a shallow depth of field -- this means that the focus of an image is relatively short which causes foreground and background objects to appear out of focus. Small apertures have a deep depth of field -- almost all the objects (foreground and background) will remain in focus.
Aperture is directly related to shutter speed for determining the amount of light that enters a camera. Large apertures combined with fast shutter speeds let in the same amount of light as small apertures combined with slow shutter speeds. Determining which combination is best for a particular situation requires photographic judgment that comes with experience.
To make it easier, most cameras have an automatic setting which will do the calculations for you. Many photographers, however, wish to control aperture and shutter speed for artistic effect.
Since a large aperture can be used in conjunction with a fast shutter speed, this is often a good combination for action shots because the fast shutter speed will 'freeze' the motion with a minimum of blurring. Large apertures can also be used for low light conditions where there is very little movement in the scene. In this situation you would combine the large aperture with a slow shutter speed.
Simple point-and-shoot cameras usually have a fixed aperture, and it is only with more expensive models that you have adjustable aperture settings. When choosing a digital camera, one consideration should be the aperture range. There are several ways this can be expressed in the camera specifications: maximum aperture, aperture range, maximum wide-angle and maximum telephoto apertures.
It is more useful to know the aperture range of a particular camera rather than the maximum apertures. A larger range gives you more flexibility in the kinds of shots you can take. A good range for all-purpose photography is from f/1.8 to f/16.
Posted by DigitalCamera at 12:35 PM | Comments (0)
June 12, 2006
Shutter Speed
A camera shutter is a mechanical device which permits light to enter the camera body for a specified period of time. The longer the shutter is open the more light enters the camera.
Many digital cameras have an automatic setting to determine the appropriate shutter speed or it may be set manually for greater artistic control.
Shutter speed is always calculated in relation to 'aperture' – the size of the opening of the lens. These two settings are used in conjunction to control the amount of light that hits the image sensor.
Fast shutter speeds are used to 'freeze' action. Longer shutter speeds can be used in low light conditions and to allow moving objects to blur. This effect is often used when photographing running water.
Since a fast shutter speed lets in less light than a long shutter speed, it is usually combined with a larger aperture setting to allow sufficient light to reach the image sensor. Similarly, long shutter speeds are combined with small apertures.
Shutter speeds are measured in fractions of a second in an approximate 2:1 scale starting with 1 second. The scale runs 1 second, 1/2 second, 1/4 second etc. down to the fastest speed of 1/8000 second. In addition, many cameras have a 'B' shutter setting (the shutter stays open as long as the button is pushed) and a 'T' setting (the shutter stays open until the button is pushed again).
Aperture settings are also measured on the same 2:1 scale. This allows for the same light exposure by increasing shutter speed one notch while opening the aperture one notch. Light conditions for a given scene allow for a range of shutter speed/aperture combinations. There is no 'correct' combination – it depends on what kind of effect the photographer hopes to capture.
For example, if you wish to photograph a moving subject such as an athlete during a sports competition, you would normally use a fast shutter speed to freeze the action. This fast speed must be used with the correct aperture to expose the image correctly.
A slower shutter speed, however, could be used if you pan the camera to match the movement of the athlete. This can create a more dynamic effect as parts of the picture (especially the background) will be blurred. Slower shutter speeds must be compensated for with smaller aperture settings.
Flash adds another dimension to the aperture/shutter speed equation. Interesting effects can be achieved by using flash to freeze the main motion while allowing some of the action to be blurred with a slower shutter speed.
Posted by DigitalCamera at 12:44 PM | Comments (0)
June 11, 2006
Color Balancing
The human eye can easily adapt to different light conditions so that objects maintain their 'true' color. If we look at a blue ball, for example, we see the same shade of blue indoors and outdoors and under cloudy or sunny conditions.
Each type of artificial light also has a particular color cast. Incandescent lighting is yellowish and fluorescent lighting can be either blue or green.
All of these different lighting conditions affect the color balance in photographs.
Most digital cameras allow you to adjust the color balance for different types of light. This can be done manually or automatically, although the automatic settings can produce uneven results from one picture to another.
Manual settings can be done by selecting a preset such as 'sunlight' or 'cloudy', but these settings can be fine-tuned to match very specific lighting conditions.
Color balance is achieved by adjusting the camera so that 'white' is truly 'white'. Once the camera is set to correctly reproduce white, the other colours should appear to be their natural shade. This can be quickly checked by looking through the viewfinder of your digital camera. Holding up a piece of white paper in front of the camera will allow you to see whether it is the correct shade or not.
Some cameras can be set this way -- place a sheet of white paper in front of the viewfinder and select 'Auto Correct'.
Remember that the presets are general guidelines and may not be suitable for every type of lighting condition. If your camera has a setting for florescent lights, for example, it may still require further tweaking to get the correct colour balance.
Although it is best to try to get the proper color balance when you are taking photographs, the colour of an image can also be adjusted using software. This should not be thought of as an alternative to proper color balancing, but it can be used to good effect on some digital images.
Some computer software can automatically adjust color as well as brightness and contrast. Start out with these 'auto' settings -- sometimes the results can be surprisingly good.
If you wish to adjust the color manually, some knowledge of the physics of color is necessary. All color is made up of the three primary colors -- red, green, and blue. Three other colors called the 'subtractive primary colors' are obtained by removing one of the primary colors where the other two are mixed. The three subtractive primary colors are yellow, cyan, and magenta.
Posted by DigitalCamera at 12:46 PM | Comments (0)
June 08, 2006
Preview Screens and Viewfinders
Traditional cameras use viewfinders which allow you to set up your shot and, in the case of Single Lens Reflex (SLR) cameras, focus your subject. Viewfinders can also be found on digital cameras, but in addition, almost every digital camera is equipped with a LCD preview screen.
Another reason for using the viewfinder is that LCD screens can be difficult to see in bright sunlight. There are many other uses for preview screens, however, and they are essential for most digital photographers.
Preview Screens
Even if the preview screen is not used for composing shots, it still provides a number of useful functions.
If you are running out of space on your memory card and wish to take a few shots more, previewing saved images allows you to pick out pictures which can be deleted. Some cameras have a thumbnail function which allows you to view many shots at once. This makes it easy to zero in on one particular photograph.
For those who print pictures directly from the camera, the preview screen allows you to select which picture should be printed. Some cameras even have basic editing functions which allow you to crop images and adjust colour and brightness before printing them. These functions can be accessed with the LCD preview screen.
Viewfinder
If your digital camera has a traditional style viewfinder, it should be used for most of your picture taking. As we mentioned above, using the viewfinder instead of the LCD preview screen will save on battery power. It will also allow you to hold the camera steadier and move the camera smoothly for action shots. Photographers who wear glasses can get a camera with a diopter adjustment -- this adjusts the lens of the viewfinder so that you don't have to wear glasses when shooting pictures.
There are some situations, however, when using the preview screen instead of the viewfinder is recommended.
The viewfinder is slightly offset from the lens. In most situations this is not a problem, but for close-up shots there can be a noticeable difference between what the lens sees and what the viewfinder sees. The preview screen allows you to precisely compose close-up shots because it shows exactly what the lens sees.
Another time it is better to use the preview screen is when shooting objects close to the ground. This saves you from having to get into an awkward position in order to set up the shot.
Through the Lens Viewfinder
Some of the more expensive digital cameras have a viewfinder which is connected to the lens with a prism. This allows you to see exactly what the lens sees. A variation on this type of viewfinder is the electronic viewfinder (EVF). This is a miniature LCD display which collects light from the lens area. As you are setting up a shot you can also see all of the camera's menus. This lets you change camera settings as you are viewing a scene for immediate feedback. Used in conjunction with a diopter adjustment, this saves the photographer using reading glasses in order to adjust the camera.
Posted by DigitalCamera at 12:55 PM | Comments (0)
June 02, 2006
Imaging Problems – Part Two
Noise is the most troublesome imaging problem but it is not the only one. Other problems related to colour, contrast, detail and sharpness may also be experienced.
Most cameras can be set to automatically adjust the white balance. This setting is usually the most appropriate but for tricky light situations the automatic setting may be turned off to allow the photographer to manually adjust the camera. This can also be used for artistic effect -- a white balance set to an extreme can produce weird, unearthly colors.
Most of the time, however, accurate color reproduction is desired. Inaccurate colors can be compensated for with imaging software, but it is always good practice to capture the best colors at source.
Improper exposure times can also be corrected with software, but again, it is better to try to capture the best image possible. If you have the opportunity to re-shoot a scene which has been improperly exposed, by all means go ahead and try to improve the image. However, if the scene cannot be re-created, save the image and try to work on it with software.
Of all the imaging problems, those caused by poor quality lenses can be the most difficult to correct. Quite simply, a bad lens is going to give you bad images. That is why it is essential to choose a digital camera with the best quality lens you can afford.
However, even good quality lenses can produce distortion at their extreme focal lengths. This is usually easier to correct as the distortion will most likely be in terms of inaccurate horizontals and verticals. Imaging software can be used to compensate for minor variations in straight lines, and the slight irregularity in these situations are sometimes not at all unpleasing.
It is almost impossible, though, to clear up a blurry image caused by a cheap plastic lens. If image quality is important to you, be sure to get good-quality glass lenses and keep them well maintained. Dirt and dust on lenses can cause distortion and noise in the final image, so keep them as clean as possible without excessive handling. A soft brush and a blower should be all that is needed if the lenses are kept covered when not in use.
Most of the imaging problems discussed above can be fixed using software. Professional imaging software such as Photoshop can be used to correct color irregularities, white balance, lens distortion, incorrect exposure, and blurring. Although Photoshop has a steep learning curve, many of the same functions are available in other software packages which are easier to use and less expensive.
Digital photographs, after all, are computer data which can be manipulated down to the bit level, so it is always possible to change the minutest detail of any image. Software can automate many of these corrective functions, and manual manipulation is also possible to improve any digital image.
Posted by DigitalCamera at 01:00 PM | Comments (0)
June 01, 2006
Imaging Problems – Part One
Many people have unrealistic expectations of digital photography. They may believe that digital photographs are 'perfect' in terms of color and detail. In fact, many problems can occur -- some of them are an inherent part of the digital domain, while others can be caused by incorrect settings on the camera.
Traditional photographs also have imperfections which have come to be an accepted part of the photographic medium. Film grain is a pattern of noise which is created by the film emulsion and is often used for artistic effect. Digital photography is expected to be much 'cleaner' than film, however, so noise levels have become an important measure of the quality of digital images.
There are several different sources of noise in digital photography. It is essentially a byproduct of the process of converting light into digital numbers. The individual photosites which make up an image sensor function by converting photons into electrons, and because of the somewhat random fashion that photons arrive at the photosites, the conversion to electrons can produce unwanted artifacts.
Noise can also be produced during the amplification of the electrical signal produced by each photosite. Because the electrical charge is so small it must be amplified to a usable level. The noise produced during amplification can be thought of as 'static' similar to that found in radio broadcasts, although in this case the static produces visual artifacts.
Reducing Noise
There are several things you can do to keep noise to a minimum. It is most noticeable in shots with extended exposure times or high ISO settings. ISO settings are related to film 'speed' -- high-speed film can capture images at very short exposure times. This is ideal for action shots such as athletic events. High ISO settings in digital cameras, however, produce more noise than low ISO settings.
Similarly, long exposure times also introduce excess noise. Long exposure settings can be used to take pictures in low light conditions such as dimly lit interiors. Keeping ISO settings low and exposure times relatively short will minimize noise as you take photographs.
Removing Noise
Noise can also be dealt with after the photograph has been taken. There are several software packages which are specifically designed to remove noise artifacts. They work by applying 'camera profiles' to reduce noise typically caused by specific camera models. Noise reducing software is easy to use and relatively inexpensive.
The problem with camera profiles, however, is that they will never exactly match the noise produced by your specific camera. In order to get the best noise reduction possible, a very simple technique can be used.
After taking a photograph which you expect will be affected by noise, take a second photograph with the same camera settings. This second photograph must be completely black -- the camera shutter must be closed, the viewfinder covered, and ideally the camera will be placed in a bag to prevent any light from entering the camera body.
This second photograph can be used as a 'noise profile' that will almost exactly match the noise of the first photograph. The noise profile is used in photo editing software such as Photoshop to subtract the noise from the first photograph. The best results will be obtained with RAW files, but the technique can also be used for JPEG images.
Posted by DigitalCamera at 12:57 PM | Comments (0)
