Digital Photography - Tips

Many cameras come with built-in close-up or "macro" features that let users photograph small objects or details located only a few inches from the camera. Owners of cameras without a macro feature can get closer by simply holding a photographic close-up (diopter) lens or even a magnifying glass directly in front of the camera lens. These close-up shots usually work best in natural light or when the subject is illuminated by a spotlight or lamp. When flash is used, the subject is often washed out due to overexposure caused by too much flash lighting. That's because the built-in flash is normally most effective in the "typical" flash range of six-to-twelve feet and is not able to reduce output to the degree needed for close ups. Even advanced digital cameras that adjust electronic flash when in macro mode can make errors and overexpose. Fortunately, there are some very simple tricks that improve the situation. If you have an advanced camera, first, see if it has exposure compensation. Sometimes decreasing the exposure using the "plus-or-minus" exposure controls will do the trick. A few professional cameras will also allow you to cut the light output of the flash in half or quarters. And if your camera offers full manual control, you can choose a smaller f/stop to cut back on the exposure. But if you are one of the millions of users without these advanced controls, there are other easy ways to take care of the problem. Most involve simply placing some kind of semi-transparent material in front of the flash to physically reduce the light that reaches the subject. The quickest fix is to use a small sheet of white paper to cover the flash window. Try a single layer first and if the flash is not reduced enough, simply fold the paper so that two layers are in front of a flash. Be sure not to cover part of the lens! You'll need to experiment with several shots to find the exact number of layers required to produce the proper exposure. You may also want to try moving the paper from directly in front of a flash window to a short distance from it, which can influence the flash coverage and reduce "hot spots." If you plan to do a great deal of close-up work with a simple camera, a more elegant solution can be found around the kitchen or living room. Many products come with white opaque plastic material in their packaging. These include the press-on lids from coffee cans, some plastic bottle caps, and our favorite, the white plastic containers used to hold videotapes. Using a sharp knife, cut enough plastic to completely cover the flash window and a bit more. Depending on the configuration of your camera, you may be able to cut a large piece of plastic and fold it at a right angle so that it fits flush to one side of the camera, where it is held in place either by your finger, a piece of tape or a more permanent hook and loop fastener. Again, it is important to experiment both with the thickness and opacity of the plastic. This will not only control light output, but the amount of diffusion. When taking close ups of small shiny

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objects such as jewelry, you may find a big difference in the final results depending on the material used to reduce the flash. If you are going to shoot a large number of objects using this technique, try to leave a small airspace between whatever material you use at the front face of the flash window. Each flash produces a small amount of heat. While there is certainly no danger of fire, the slight suppression of this heat over a long period of time could cause a discoloration of the plastic window directly in front of the flash tube. And, of course, the best thing about digital photography is that you can experiment and see the results right away at no cost! Experiment making mini versions of the many diffusers used by the pros! Try mounting a piece of plastic or paper with some tiny holes punched in the material to allow a percentage of the full flash to strike the subject. Experiment with diffused flash for close-up portraits or "head shots" as well! Have fun and get creative with your digital camera!

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There are various ways to correct for color in Photoshop. This method is one of the easier ways and can achieve some very nice results. Here is an example of an image we corrected using Photoshop. Curves

Setting the Black Point

Open your image in Photoshop and select Image > Adjust > Curves. Click the black Eyedropper in the task bar that comes into view. This eyedropper is just below the auto button on the far left. Click on the blackest part of the picture, which in this picture is the man's shirt. If you open the info

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palette, it can help you determine the darkest and the lightest values. If you look at the CMYK area of the info palette, you will notice that when you scroll over the picture with the eyedropper the numbers change. Look at the percentage after K (K represents the color black). The higher the percentage the more black there is in the pixel. This can help you determine the darkest pixel in your photo.

Setting the White Point

Now take the white eyedropper, which is the dropper furthest to the right, and click on the area that represents what you think is the whitest area in the picture. Remember to look on your info palette at the CMYK area. The lightest pixel will have the lowest percentage after the letter K. Color Balance

In this picture we find that, with the exception of the man's face most of the colors are pretty correct. However, if you find that your picture has a slight color cast, select Image > Adjust > Curves or Levels, select your gray eyedropper which is the middle of the three, and click on what you believe to be the most colorless or neutral gray area of your photo. If this doesn't remove the color cast, then use the color balance dialog box found under Image > Adjust > Color Balance, and adjust the color until you believe you have found the most accurate color for your photo. For problem areas follow the instructions below.

After correcting the curves, we still find that there are problem areas within the picture. The man's face is too red. Take your polygonal lasso found in the upper-right square of your tools palette and select the area around the man's face and neck. It does not have to be a precise selection as long

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as it is within the flesh areas, and the background or clothes are not selected. After you have selected the area, go to Select > Feather. A dialog box will appear asking how many pixels you would like to feather. Depending on the size of the selection you would feather about 20% of the pixels selected. That is to say, if you had ten pixels selected you would feather two, one hundred you would feather twenty and so on. After you have feathered the selection, go up to Image > Adjust > Color Balance. Select the red channel and there you would set the sliders to remove or replace color that is too predominant or lacking, until you come up with something pleasing.

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Now that the color has been adjusted, it's time to Sharpen the image. If you are printing out this image, then be sure to size it before you sharpen it. You may lose some of the sharpening effects if you size it after you sharpen.

Select Filter>Sharpen > Unsharp Mask. A dialog box will appear with a small preview window. Your cursor will now be in the shape of a little box. If you are sharpening a portrait, place the box over the eye so you can review the sharpening process as you slide the bar. You will notice that the dialog box, offers three areas to consider: amount, radius, and threshold. Amount is the percentage of sharpening that will be done to the edges of the image. Radius is how many pixels in from the color edge will have their pixels sharpened, or alternatively how thick you will choose to make the edge (the higher the radius, the thicker the edge). Threshold is how different the color shifts in the pixels have to be before the filter sharpens them. So if you are sharpening flesh tones, you probably want to increase the threshold to avoid sharpening any grain or noise in your picture. More abrupt color changes can take a decrease in threshold. Also it is better to sharpen at lower percentages twice for a smoother look, then to run it once at a percentage that is twice the number. And remember, always make "Sharpen" the last thing you do in the image-editing process.

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White balance If you are a bit unsure of the use of the white balance setting on your camera, then this simple explanation may be of help. Without getting too technical, it is important to understand that a digital still camera needs to establish a basis from which the percentage of each colour is derived. White, the sum of all colours, needs to be decided each time the camera takes a photo, one of the reasons digital cameras tend to be a bit slower off the mark than their film- based cousins who leave that nagging detail to the film. Since white is affected by the lighting environment, the camera must be able to compensate for the effects of this light, on white. The importance of this to the user is that having to adjust the colour balance of an image can be complicated after the fact, however versatile the image editing program.

Most digital cameras, in particular the newer models, offer an adjustable white balance. Usually, the various settings fall into the following categories: AUTO WHITE BALANCE This setting is always the default on digital cameras. Complex algorithms, programmed into the camera's firmware, decide where the white point is. Mostly this is a fairly accurate system, but it is far more successful at deciding the correct white point when used outdoors and in bright conditions. Under a cloudy sky, many auto white balance systems will fare less well, and can cause blue- tinged images. TUNGSTEN

2 photos are taken under the same incandescent light and without flash. The section on the left is photographed using the Incandescent (Tungsten) white balance setting, while the section on the right uses the camera's Auto white balance.

Also called "incandescent ", or "indoor" on some cameras. This setting is intended for use when the lighting environment is mostly light bulbs, such as commonly found in a home. When the white balance system of the camera "knows" that the photo will be taken in this type of environment, without flash, then it is better able to decide where the white point should be. This is the setting that should be used when taking photos indoors, without the flash.

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FLUORESCENT This setting is for adjusting the white balance when taking photos under fluorescent tube lighting. Some cameras offer more than one fluorescent adjustment since there are different types of fluorescent tubes: cool white and warm white. These different fluorescent lamp types are used in many work places and the type used follows no rules. The photographer must decide which type it is, to best use the white balance settings available on the camera.

2 photos are taken under the same cool white fluorescent light and without flash. The section on the left is photographed using the Auto white balance setting, while the section on the right uses the fluorescent setting.

Of all the settings to use, this one is the most difficult to determine. For example, many offices and schools use a mix of these tubes to soften the harsh cold light produced by all cool white tubes, by adding the peach coloured tinge of the light that emanates from the warm white tubes. In such circumstances, experimentation is best. SUN, CLOUD, SHADE, OR OUTDOOR

Under a partly cloudy sky, the results of Auto white balance and the Cloud setting.

These settings are not offered on all cameras. Generally, white balance systems are optimized for outdoor situations. Therefore, they can handle setting the white balance easily. Still, some manufacturers add extra settings to their cameras. The actual uses of these settings can depend on the particular camera. It is best to consult the manual to determine the intended use, since, on one camera it might be intended for very "intense sun", and "setting sun" on another.

ONE -PUSH , USER PRE-SET, MANUAL, OR WHITE BALANCE HOLD Many different names are used to describe the same concept. All of them describe a white balance setting decided on the spot, under the lighting conditions that are prevalent where the photo is to be taken.

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Usually, the user is required to point the camera at a "white" surface and select it as the white point. The difficulty comes in deciding what is "white". An example of that difficulty can be seen with plain white paper. Different stocks of white paper will present different "whites". Some might be more yellow, some brighter white. Under lights affecting our perception of white, how is one supposed to determine what is "truly" white? One way to deal with the problem, is to carry a small rectangular piece of white paper along with the camera. We have found that a small square of very white paper works well. Then, when the white balance setting is critical because the photo opportunity may not present itself again, establishing the white balance on the "reference" white paper can work well, provided it is used to balance the white in an indoor situation

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If you wonder what focal lengths, zooms and digital zooms are, and how they work, then this little explanation might be of some help.

First, let's look at what is a focal length. We will use 35mm single lens reflex cameras with interchangeable lenses to illustrate. Focal length is defined as "the distance between the rear nodal point of the lens and the focal plane, when the focus is set at infinity"¹. The rear nodal point of the lens "is where the rays of light appear to have come from, after passing through the lens"². The focal length of a lens is expressed in millimetres. The focal length of the lens also determines the field of view: how wide, or narrow the view through the lens is.

The photo at left shows a 35mm camera fitted with a 50mm lens. In the 35mm film format, lenses with focal lengths in or around the 50mm mark, are generally referred to as normal lenses. This is because these lenses show objects and scenery, at approximately the same scale as is perceived by the unaided human eye.

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The photo on the right shows the field of view of a 50mm lens. The image shown here is taken through the viewfinder of the camera. The scale is very similar to what an observer would see with the naked eye while standing at the same vantage point as the camera.

Now, we see the same camera, but this time, fitted with a 200mm lens. The lens magnifies the image reaching the focal plane and in turn, narrows the field of view, just like binoculars would.

Again, the photo on the left shows what can be seen throught the viewfinder of the camera. Since the image is considerably magnified, we only see a small portion of what was visible in the 50mm image, but that portion now shows much more detail than was visible previously.

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The Optical Zoom A zoom lens is a lens desig ned so that its focal length can be varied over a predetermined range. The image is optically magnified and, depending on the zoom's setting, will show a larger, or smaller field of view. The variability of the zoom lens allows it to replace a number of single focal length lenses. With a digital camera, the optical zoom does not change the image size, or the resolution. The number of pixels used to describe the image remains constant. Therein lies the difference with the digital zoom. In this example, the photo is taken with the camera's zoom set to the 38mm position, offering a broad field of view. The image's resolution is 1600 x 1200 pixels. Now, we zoom in to 115mm, maintaining the camera in the same exact position. The image still has the same resolution as the previous one: 1600 x 1200 pixels. Similarly, the number of kilobytes used to store the image file without compression, will be the same as the photo above. The optical zoom has brought the subject "closer", showing more detail than was visible previously, as if the camera had been moved physically closer to the subject.

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The Digital Zoom Digital cameras equiped with a single focal length lens, usually offer the possibility of mimicking a zoomed image. The system is called a digital zoom. With single focal length cameras, the process works by capturing only the central portion of the entire image received by the sensor. In a real sense, the digital zoom is really only a cropping tool, since it cuts off the parts of the image that would be out of the field of view if a longer focal length lens had been used. The image above shows the "zoom" possibilities. For example, if the real image has a size of 1600 x 1200 pixels, a 2.5X digital zoom would capture a smaller image measuring only 640 x 480 pixels, taken from the centre of the frame. In the illustration above, the white rectangles indicate other possible digital zoom options. Inherent in a digital zoom, is the fact that the numbers of pixels used to capture the image is the same, as the number of pixels representing the same area on the original, non- zoomed image. Therefore, the digital zoom image is either smaller than the image it was cropped from but has the same definition (the same the number of pixels are used to represent the same area), or, if the image is re- sized by interpolation to be of the same size as the non-zoomed image, it exhibits a much lower definition. Since the physical number of pixels that captured the image is always constant, resizing the image by interpolation has a serious impact on the quality of the image itself. The best way to demonstrate this is to look at the examples below:

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The image shown on the right is an un- cropped reduction of an original photo which measured 1600 x 1200 pixels. The image is captured with a single focal length lens of 40mm. To show the effect of a digital zoom, we selected a 640 x 480 pixel portion from the central part of the original frame (white rectangle). Then, we re-sized this new smaller image to the same measurements as those of the original photo: 1600 x 1200 pixel. Resizing the smaller cropped image has the effect of lowering the definition. We cropped each photo (represented by the smaller yellow rectangle in the illustration above), so they could be placed side by side below.

This is a 280 x 210 pixel portion of the original image, showing the definition of the non-zoomed image. The definition exhibited here is normal for a distant object, imaged by relatively few of the sensor's pixels.

This is a 280 x 210 pixel portion of the zoomed image. The interpolation of the original image data has caused the photo to become quite blurred, as the interpolation algorithm "invented" pixels to increase the image size.

What is important to remember, is that the very same thing can be accomplished with just about any photo editing program. A photo can be cropped to what ever is required, with greater flexibility than the digital zoom provides, since any given area can be selected.The digital zoom on the other hand, can only use the centre portion of the entire frame. If there is an advantage to the digital zoom, it is that since the camera meters only the "zoomed" section of the image (a smaller section at the centre of the frame), it can quite often generate a better exposed image for that particular area, than if the exposure had been determined based on the larger image.

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There are as many ways to take photos as there are photographers. However, one concept affects all photos: composition. Because, for an image to be successful and meaningful, it needs to be composed correctly. Should the subject be poorly positioned in the frame, it may go unnoticed, or the meaning of the photograph may come across incorrectly.

Without getting into the many fine points of composition, there are a few basic rules that should be applied; even though, as every one knows, "rules are made to be broken"... By the same token, the rules do need to be known before they can be broken. For many centuries now, first architects, then painters of the Renaissance, and much later—during the middle of the 19th century—photographers, have used a grid based on the Golden Rule, to guide them in the composition of their images. The golden rule establishes an ideal ratio between height and width. These proportions are derived from the field of view of the human eye, and are used, often with slight variations, throughout a large number of commonly used objects . Examples can be found in architecture, in the shape of doors and windows, to more mundane items such as picture frames and sheets of paper. More or less, the ratio corresponds to 2/3 x 1/3; and this is a ratio that can be recognized in the size of most film frames and, today, in the image sizes of digital cameras. Within that frame, another rule is used: the rule of thirds. It is used to determine precise areas where the important parts of the image should be placed. The same principle is used to determine the position of the horizon and the proportion of ground to sky. When first looking at an image, the eye of the viewer rarely settles at the centre of the image, but instead follows an approximate "Z" pattern (top left to right, then to the lower left and right again). This pattern is

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most unconscious but has been well- documented. It is probably associated with the western reading pattern. From the photographer's point of view, the goal then becomes to guide the gaze of the viewer to the subject, while being aware of the way most people look at an image. Similarly, compositions containing diagonals can also be based on the golden rule and the rule of thirds, so that the resulting image is balanced.

All these rules can be circumvented intentionally, as they have been by many wellestablished artists, but they offer an important starting point for any composition. Particular care must also be used in portraits so that the gaze of the subject is not too close to the edge of the frame.

Note the direction of the gaze of the model in this famous painting at right, and the space which it is given. Also notable is the diagonal composition of the painting.

Johannes Vermeer 1632-1675 The lace maker.

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Yet, this composition method does have some limitations. When a wide angle lens is used, particular care must be given to framing and composition since this type of lens can easily cause curvature in the straight lines placed near the edges of the image frame. This is why it is generally advisable to place the horizon near the horizontal centre of the frame, so as to avoid a curvature, which in turn would detract from the wide field of view presented in the photo. The same care must be taken with vertical lines in architecture- type photos, since they too can become odd- looking curves that deform the shape of the building and ruin the composition. Digital camera zoom lenses are particularly prone to these distortions since they are usually equipped with optics that are very hard to correct totally, and will often have barrel distortion in wide angle and pincushionning at the telephoto end. So, while immediacy is at the heart of photography, a close look at the great photos of the past, those that are remembered, will usually reveal a flawless composition. Therefore, it is worthwhile to take a little time, if possible, before pressing the shutter release. A walk around the subject to find the best angle, selecting which element should be where in the frame, and visualizing the final image in the mind's eye, will greatly improve most photos. This way, a better chance will be had to capture that special something that triggered the desire to take the photo

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What it is. A good starting point to any consideration of exposure is the admission that a correct exposure is mostly "correct" in the eye of the photographer. Meaning that any under, or overexposure can be perfectly acceptable if it is part of the communication of the photographer. This said, exposures can also be looked at from a "technical" point of view. Digital cameras calculate a technically correct exposure based on the information their light meter provides. While this method works well in the majority of cases, it can, on occasion, lead to exposures that can be labelled as "technically" inaccurate. To remedy these occasional problems, most digital cameras— including relatively inexpensive ones—are equipped with exposure compensation. Exposure compensation provides a me ans by which an exposure error can be rectified. In general, cameras offer a exposure compensation range of ± (plus or minus) 2EV (Exposure Value). Many cameras allow compensation to be made in increments of 1/3 EV, while some others permit it in 1/2 EV increments.

A simple concept In exposure compensation positive values increase the brightness of the image, while negative values darker it. Probably the easiest way to explain how exposure compensation is to provide some examples of how exposure compensation affects the exposure. The subject is an old totem pole in a park. For these photos, we selected a Casio QV8000SX, as it is one of those cameras that can record a great deal of image data (see the columns below). Additionally, the QV- 8000SX is used because it has an 8X zoom, making it possible to zoom in on the top of the totem; and because of the fact that it has a good multi- pattern meter, which generally guarantees a correct exposure. A correct exposure with the exposition compensation set to "0" is important so the variations caused by the compensation can be observed.

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Compensation set to "+1EV" File Size Resolution Quality AE Light Mete ring Shutter speed Aperture stop Exposure comp Focusing mode Flash mode Sharpness Saturation Contrast White balance Digital zoom Model

: 457 kbyte : 1280 x 960 pixels : Fine : Programmed AE : Multi : 1/49sec : F3.2 : +1.00EV : Auto Focus : Off : Normal : Normal : Normal : Auto : Off : QV-8000SX

Compensation set to "0" File Size Resolution Quality AE Light Metering Shutter speed Aperture stop Exposure comp Focusing mode Flash mode Sharpness Saturation Contrast White balance Digital zoom Model

: 459 kbyte : 1280 x 960 pixels : Fine : Programmed AE : Multi : 1/96sec : F3.2 : 0.00EV : Auto Focus : Off : Normal : Normal : Normal : Auto : Off : QV-8000SX

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Compensation set to " –1.00EV" File Size Resolution Quality AE Light Metering Shutter speed Aperture stop Exposure comp Focusing mode Flash mode Sharpness Saturation Contrast White balance Digital zoom Model

: 472 kbyte : 1280 x 960 pixels : Fine : Programmed AE : Multi : 1/146sec : F3.2 : –1.00EV : Auto Focus : Off : Normal : Normal : Normal : Auto : Off : QV-8000SX

As can be seen the effect is quite dramatic. More subtle results can be achieved by increasing or decreasing the compensation in smaller increments. As a matter of fact, some cameras can do this automatically, shooting 1 frame with the settings provided by the metering, then shooting 2 other frames, one with negative compensation and one with positive compensation. The method is referred to as "bracketing", or "exposure bracketing". To show the more subtle differences in exposure that can be achieved with a lesser increments, let's consider the next 3 photos of the same subject. Compensation set to "+0.75EV" File Size Resolution Quality AE Light Metering Shutter speed Aperture stop Exposure comp Focusing mode Flash mode Sharpness Saturation Contrast White balance Digital zoom Model

: 385 kbyte : 1280 x 960 pixels : Fine : Programmed AE : Multi : 1/121sec : F3.2 : 0.75EV : Macro : Off : Normal : Normal : Normal : Tungsten : Off : QV-8000SX

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Compensation set to "0" File Size Resolution Quality AE Light Metering Shutter speed Aperture stop Exposure comp Focusing mode Flash mode Sharpness Saturation Contrast White balance Digital zoom Model

: 452 kbyte : 1280 x 960 pixels : Fine : Programmed AE : Multi : 1/211sec : F3.2 : 0.00EV : Macro : Off : Normal : Normal : Normal : Tungsten : Off : QV-8000SX

Compensation set to " –0.75EV" File Size Resolution Quality AE Light Metering Shutter speed Aperture stop Exposure comp Focusing mode Flash mode Sharpness Sa turation Contrast White balance Digital zoom Model

: 490 kbyte : 1280 x 960 pixels : Fine : Programmed AE : Multi : 1/347sec : F3.2 : –0.75EV : Macro : Off : Normal : Normal : Normal : Tungsten : Off : QV-8000SX

Just like everything else in photography, the best way to learn how to use exposure compensation is by experimentation. Sometimes, a slight alteration to the exposure dictated by the camera's meter can have an impact on the tone, and the success of the image. Darkening a stormy sea with - 1/3EV can create a foreboding mood, while increasing the compensation to +1/3EV can make a picture of a child playing on a swing look happier and sunnier

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Every time information is provided about the lens of a digital camera, the focal length mentioned is also given in 35mm equivalent. While the reason for this may be obvious to some, it also occasions questions for quite a number of people. 35mm film frames measure 36 x 24mm, and are the film frame size of the majority of film cameras in use today.

28mm focal length (wide angle)

This widespread use of 35mm film has caused many people to develop a general idea of the field of view that will be visible with various 35mm focal lengths. In other words, because of its popularity, the 35mm film format has become a reference point, much like a unit of measure such as the foot or the metre. For example, a 28mm focal length will capture a fairly wide angle; a 35mm focal length noticeably less; a 50mm lens will provide a near normal field of view, a 380mm lens will fill the field of view (see comparison lower down) with a distant subject.

35mm focal length (wide angle)

Put another way, the smaller the number of the focal length the wider the field of view and, conversely, the larger the focal length number the narrower the field of view will be; and this holds true whether for film or digital.

All focal lengths are measured in millimetres, whatever the format of the camera: 35mm, APS, or digital. The focal length number indicates the distance between the lens and the focal plane— the position of the film or sensor. The precise definition of focal length is "the distance between the focus (where the image is sharp on the focal plane) and the optical centre of the lens". (See graphic at right).

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With digital cameras, these focal length numbers are usually very small because the image sensors most commonly used today are quite small—under an inch when measured diagonally. To form an image on such a small target, the lens needs to be quite close to the focal plane, hence the short focal length numbers common to many digital cameras. 50mm focal length (normal view)

380mm focal length (telephoto view)

However, the real reason a 35mm equivalent is given, is not because people can't relate to the short focal lengths of digital cameras, but because the "real" focal length on a digital camera—for example a 6 to 18mm zoom—will not always corresponds to the same field of view on different digital cameras. At the root of this difference is the fact that different electronic image sensors —the digital equivalent of a film size—come in a variety of different sizes.

Let's take 3 different CCDs as example: § § §

a 2.1 megapixel CCD measuring 0.5 inch diagonally = (1/2") a 3.3 megapixel CCD measuring 0.55 inch diagonally = (1/1.8") a 4 megapixel CCD measuring 0.66 inch diagonally = (2/3")

As can be seen, each CCD has not only a different diagonal measurement, but a different resolution, which is to say the number of pixels that will form the image. It is important to note that the number of pixels used to form the image is not related to the the focal length. In fact, a number of digital cameras have been produced which, while having different sensor resolutions, are in every other respect, similar: same lens, same body, etc. And, if the sensors used are the same physical size, the 35mm equivalent of the lens will be exactly the same. On the other hand, if the lens employed for each CCD is exactly the same focal length, i.e. 8mm, but the CCDs have different sizes, then their 35mm equivalent focal length will be different, as each will

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show a greater or lesser field of view. (See graphic at left) So, using a "standardized" way to describe the field of view of digital cameras helps to simplify everything, irrespective of the size of the CCD in use. And that need for a common way of expressing the field of view, is why the "35mm equivalent" is generally mentioned when a digital camera lens is described

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The depth of field defines the zone in which all elements show clearly from foreground to background. The depth of field in an image is controlled by three factors: the distance to the subject, the focal length, and the aperture used to capture the image. This article is an attempt at explaining a subject which appears simple superficially, but is in fact quite complex, and one for which explanation often comes through the guise of formulae and equations. We thought we would approach the topic in more general terms, and avoid peripheral ideas such as depth of focus, the hyperfocal point of a lens and optical concepts such as circles of confusion. Instead, we seek to explain the observable difference between the depth of field of a digital camera that uses a small- size CCD, and others that use larger imagers or film. Before anything else, it is necessary to understand that the term depth of field defines a somewhat "elastic" concept: acceptable sharpness. The perception of sharpness can differ from one individual to another, and when the expression depth of field is used, it really denotes that area in an image that exhibits a sufficient sharpness to be considered more or less in focus. The depth of field doesn't have be one of precise sharpness, but instead that portion of the image in which things — or people — remain recognizable for what they are. For users of compact digital cameras, depth of field is a subject of special interest because depth of field is more difficult to control with a compact digital camera than with earlier film cameras. The small imaging sensors of compact cameras require the use of short focal lengths, and this in turn gives these cameras an unusually long depth of field when compared to 35mm cameras. Thus, intentionally getting a shallow depth of field is more difficult. The influence of subject distance on depth of field: As a rule, depth of field decreases as the subject gets closer to the camera. Meaning that as the point of focus gets closer to the lens, the possible extent of the depth of field diminishes. On the other hand, if the subject is far enough away from the camera — and for compact digital cameras, this need not be very far — the depth of field extends out to infinity.

Focal length and focal plane: To understand the relationship between the focal length of a lens and the perceived depth of field, some terms need to be defined. The graphic below, (based on a graphic © Olympus America), illustrates the meaning of focal length and focal plane:

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Focal length describes the length of the lens, as measured in millimetres, from the focus point in the lens, to the focal plane. The focal plane is the area — in this case the area of the sensor — that needs to be covered by the circle of light focused by the lens. The physical dimensions of the lens are determined by the need to cover the entire focal plane. As the diagonal of the focal plane represents its longest dimension, the diameter of the circle of light created on the focal plane by the lens must exceed the diagonal measurement of the focal plane. Therefore, in the case of a 1/2-inch sensor, to ensure complete coverage of the sensor, the circle of light focused by the lens must be larger than the diagonal of the sensor when it arrives at the focal plane. With a 35mm camera, that same coverage must be even bigger since the area to be imaged is larger — hence the need for a bigger and longer lens. As a corollary, the longer the lens' focal length, the shorter the possible depth of field will be. In other words, as the focal length of the lens increases, the depth of field for any given aperture, becomes progressively shorter as long as the position of the lens, relative to the subject, remains unchanged. The reverse also holds true. As the focal length gets shorter, the possible depth of field becomes progressively longer. Furthermore, the depth of field is usually uneven divided between the front and the back of the focus point. For shallow depths of field, the division is almost equal, with the far depth being a bit greater. When the near depth extends one quarter of the way toward the camera, the far depth will extend twice that depth behind the focus point. By the time the near depth of field has reached half the distance to the camera, the far depth has gone out to infinity and everything beyond the focus point will be in focus.

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The relationship between aperture and depth of field Not only does the physical length of the lens impact the depth of field, the depth of field is also impacted by the aperture used to capture the image. The aperture of the lens is the opening that controls how much light gets to the sensor. In a camera with a variable aperture, a mechanism called a diaphragm, or iris, is used to restrict the amount of light that travels through the lens. The diaphragm provides control over the exposure, as well as the depth of field. The diaphragm can be made as simple covers with holes that provide different apertures, or composed of blades that are adjusted incrementally to provide varying apertures. The illustration below shows the relationship of aperture to depth of field: (Note that the f-numbers shown below are just examples of the relationship, and do not precisely correspond to the lens apertures shown.)

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So, as the f-number representing the aperture increases, for example progressing from f2 to f11, the depth of field increases — which provides an easy way to remember the relationship: small f-numbers = less depth of field, big f-numbers = more depth of field.

The influence of focal length on depth of field As mentioned previously, short focal lengths have an intrinsically long depth of field. Since compact digital cameras use short focal lengths, obtaining a long depth of field — where elements from foreground to background are clearly recognizable — isn't a problem, but obtaining photos with a shallow depth of field is more difficult. In fact, in wide angle (the shortest focal length), and at distances of more than 3 or 4 metres (9 to 12 feet) the depth of field of a compact digital is very long, and the aperture's primary role is more to control the amount of light reaching the sensor and therefore the exposure, than the depth of field. Unlike with a 35mm, for the compact digital the subject needs to be closer to the camera for the influence of the aperture to become observable. This is demonstrated in the images below, both of the same subject, photographed from approximately 1 metre (3 feet) away at f1.8. The lenses are set so as to have a similar focal length as is evidenced by the width of field.

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This first photo is captured with a compact digital that uses a 1/2-inch CCD. The lens' aperture is set to f1.8, the maximum possible with the camera. As the background is a relatively short distance behind the subject, the large aperture only blurs it slightly. Details such as the pine needles on the ground at the base of and behind the flower remain visible, and readily recognizable. This second image is capt ured with a digital SLR camera equipped with a much larger CCD which allows it to use standard 35mm lenses. As can be seen, the longer lens means that the depth of field at f1.8 is much shorter. The pine needles in the background are not recognizable as such, and the outline of the rocks is very soft. If a long depth of field is "natural" for the compact digital, it also means that purposefully obtaining a shallow depth of field is bound to be more difficult. Controlling the depth of field with a compact digital camera Control over the depth of field means being able to select whether the image will have a long, or a short depth of field. With most compact digital cameras, this can be quite challenging, and in some cases almost impossible. Yet, a short depth of field is very useful for some types of photos, particularly portraits. With a portrait, the photographer generally wants to make the subject appear detached from the background, as the latter can be distracting. One way to mitigate — to some extent — the long depth of field of a compact digital and obtain the appearance of a shallower depth of field, is to place the subject at least a few meters in front of the background, and use the optical zoom to frame the subject. This technique places the background on the outer edge of the depth of field.

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The image at right, and the one below make use of these two factors wile highlighting the different depth of field created by the aperture. The rhododendron in the background is approximately 3 metres (9 feet) behind the zebra, and the zebra itself is about one metre (3 feet) from the camera. By zooming a bit, and selecting a wide aperture of f2.2, the background becomes suitably blurred. The same subject captured with an aperture of f11 shows the background clearly, and the difference between the two images illustrates the advantage of a shallow depth of field for portraiture. With a clearly defined background the zebra's head looses its dominance, as the busy background detracts attention. Often, the use of the zoom is more important as a means to frame the subject and avoid any potential wide angle distortion. Although increasing the focal length used for the image can also be seen as a means to decrease the depth of field, much depend on the particular camera used. While some will have an aperture range that is sufficient to provide control over the depth of field, others will exhibit little difference between an image captured at f2.8 and one shot at f8

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Cameras tend to dust and fingerprint magnets, and cleaning them without causing some accidental damage can be a bit worrisome. Yet, a good cleaning can be done with some simple supplies and, if done carefully, will help keep a camera looking new for years. Many cameras come with little stickers on them. Witness the number of cameras that can be seen, years old, still sporting their little oval "OK Passed" sticker, its gold colour faded and its edges peeling. Many people avoid removing these things because they worry that the attempt will damage the finish of the camera. In fact, leaving those stickers on is often a mistake. As time passes, many surfaces exposed to light change colour slightly — even metallic ones — and the adhesive of the sticker may well become permanently etched into the finish. Moreover, they have no value as they simply indicate that the camera was quality inspected after assembly. Removing these and others like it doesn't invalidate a warrantee, nor c ompromise the resale value of the camera. To clean a camera properly, one has to adapt the products and methods used to the specific camera. Different surface finishes require different handling. For example, a plain plastic with a silver finish isn't very strong and any cleaning of the surface should be done with great care to avoid rubbing off the finish; on the other hand, a metal finish is usually quite rugged and can be cleaned easier. This is why prior to any first-time cleaning, it is important to determine with some degree of certainty the composition of the surface. Most camera bodies have some sort of compartment which, when opened, can be used to determine the finish of some the camera's surface. A good place to look in is the battery compartment. Often the cover will be made of plastic, but the body may not be. A look inside the cavity for the battery can reveal the type of finish used. In the case of the photo at left, the camera has a silver finish on the outside, but a look inside reveals a light grey plastic. This is a surface where the exterior finish is like a paint, and therefore a fragile surface.

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The same thing can be done to determine if the camera has a metal body and the type of finish it has. In the photo at right, when the battery compartment is opened, the metal casing of the camera is visible (1), next to the plastic inner body (2), and so it the fact that in this case, the metal surfacing has a paint finish. Once it has been determined how the body is finished, cleaning it becomes a lot safer.

Some cleaning materials are required: § § § § § §

A good but mild liquid glass cleaner, the type that has a pump bottle (not Ammonia!). Cotton swabs. A small bottle of Isopropyl alcohol A compressed gas (or compressed air) duster. A lint-free cloth such as an old, but good quality cotton, handkerchief or napkin (no starch). Some common sense and caution.

Cleaning the body surfaces: Usually, all it takes is a soft, clean cotton cloth. Exhale gently on the part to be cleaned and rub lightly. For a greasy stain, mix approximately 50% glass cleaner and 50% water, dampen a bit of the cloth and rub lightly. To remove glue from a sticker, use a few drops of Isopropyl alcohol on a clean cotton cloth. Be careful not to rub hard; it could remove the finish. Never use Isopropyl alcohol on bodies with a textured surface, or those made of plastic, the alcohol can dissolve the finish, removing the paint or smoothing the texture. Dust can be blown out of crevices and joints using a compressed gas or air can. Always hold the can vertically and never bring the nozzle too close to the camera, or use the spray on any surface with a mirror. Compressed gas is very cold and can cause condensation while the strength of the jet can force humidity into the body. Maintain a distance of 4 to 5 inches at all times, and use very short bursts.

Cleaning the lens: There are a lot of gadgets to clean lenses on the market. The fact is a simple lintfree cotton cloth works as well, if not better. Be particularly wary of two cleaning products. One is a gadget with a small round

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pad at one end for cleaning the lens. The cleaning pad is glued, and the glue can start to melt if the lens cleaner has been in a warm place. The glue will then end up on the lens and be difficult to remove without damaging the coating of the lens. The other is lens tissues. Whatever the paper, it is best to avoid use of any kind of paper product directly on the lens of a camera as the fibres can be quite abrasive. Cleaning the lens of a digital camera can be difficult. Many models have very small lenses, and others with zoom, are sensitive to lateral movement. Moreover, some cameras have an automatic barrier that covers the lens when the camera is powered off. To clean the lens of a camera with a lens barrier, turn the camera on and remove the battery or batteries. This prevents the camera turning itself off while the lens is being cleaned, and prevents unnecessary wear on the battery. Remember that lenses are fragile, do not push hard, and avoid putting any lateral pressure on the lens. Whether the lens has a large front element, or a small one, the first step is to blow some air on its surface to remove anything that might scratch it when it is cleaned. Maintain the compressed air can upright, and shoot small burst of air at an angle from the lens. Do not use long bursts and do not bring the tip of the nozzle closer than 3 inches. Use a cotton cloth to wipe the lens, while exhaling directly on the glass. For the areas that the cloth does not reach, use a clean cotton swab to gently dislodge the dust. A cotton swab must be used extremely gently, and never press on the tip, always use it at an angle, and never use a chemical. For lenses with a larger front element, a cotton cloth works best. Here again, after spraying a burst of compressed air at the lens, simply exhale lightly on the glass and wipe with a good quality cotton cloth. This should remove most stains. Water rings, from rain or other moisture, can be quite stubborn. Any water droplets should be dried right away and not allowed to dry on the glass. Afterwards, some compressed air should be able to blow any remaining dust and lint away.

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Cleaning the viewfinder: Because it is so close to the eye when the camera is in use, dust in the viewfinder can be quite noticeable, and cause blurred areas in the image. For some cameras, the viewfinder can also be the most difficult to clean because the space is so small. The most difficult viewfinders to clean are those that are deeply recessed, when the lens of the exit pupil is far inside the body. The glass, or optical grade plastic, of most viewfinders have no outside coating, and therefore it is safe to use a mix of 50% glass cleaner and 50% water to clean them. Touch the extreme tip of a cotton swab to the mixture. The tip must be damp, and not soaked. If it is too wet, squeeze out the excess before gently touching it to the surface of the viewfinder. Use a gentle side to side motion without applying any pressure. Then, immediately use the dry end of the swab to gently wipe the glass or plastic. Do not allow the cleaned surface to air dry. Any dirt or dust remaining in the corners can also be removed. Use a new cotton swab dampened slightly with the same mixture on the tip and let it sit in the corner for about 10 to 15 seconds. Then dry the area with a fresh swab and use compressed air to blow away any remaining dust or lint. Rubber eyecups and rubber grips: The rubber used for some parts such as the grip, or the viewfinder eyecup, attracts lint, dust etc. To clean these parts, use Isopropyl alcohol. Dip a cotton swab in the alcohol and squeeze its tip lightly between the fingers to wring out excess alcohol. Using the cotton swab, wipe the eyecup or grip evenly. Do not use an excessive amount of Isopropyl alcohol or the drying alcohol will leave streaks. Avoid going to close to parts — such as a painted and textured body surface — that might be stained or damaged by the alcohol. As soon as the rubber part is wet with the alcohol, dry it with compressed air.

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Cleaning the LCD screen: There are different types of surfaces for LCD screens. Some are non- reflective and lightly textured, some have a shiny protective glass or plastic. Whatever the case, the LCD screen is fragile. Any strong pressure on its surface can damage it. The LCD screen should be cleaned the way a lens is: with a soft lint-free cloth. Exhale on the surface lightly and wipe away fingerprints or nose prints. For stains that don't come off with just a cloth, use a cotton cloth moistened with a mix of 50% glass cleaner and 50% water. The cloth should be damp to the touch, not soaked. Gently moisten the stain, then wipe with a clean dry cloth.

Memory card compartment: Never insert anything other than a card into the memory card compartment. There are small and very fragile contacts inside that can be damaged easily. If cleaning is required — for example the camera has been used in a very dusty environment — the best way to clean the card slot is with compressed air. When using compressed air or gas, the same rule always applies: do not insert the nozzle into the card slot; and do not spray from too close a distance or otherwise moisture will get into the camera. Maintain at least a couple of inches between the tip of the spray and the card slot; and clean dust out using short, quick bursts.

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Battery compartment: Battery contact can become soiled over time and affect the performance of the batteries. The common way of cleaning these is with the small eraser at the end of a pencil. The eraser will remove most dirt and even some light corrosion. Once the contacts are cleaned, then blow air into the compartment to remove the remaining bit of eraser and dirt.

A word of caution: The cleaning methods presented here are based on experience and should work with most cameras. However, if you decide to clean your camera yourself, be careful, work slowly and gently as ultimately, you are responsible for your actions. Remember that such things as cleaning solutions and alcohol are solvents and if used inappropriately or carelessly can damage the camera. If you are unsure what to do, have the camera cleaned by a technician. It is better to spend a bit of money to have your camera cleaned than to damage it.

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