There are three basic settings that determine exposure:
- aperture -- the size of the opening inside the lens. The larger the hole, the quicker the sensor will get exposed to light.
- exposure time -- this is quite obvious, too. If the sensor is exposed twice longer, the amount of light reaching the sensor will be doubled.
- ISO -- this is the sensivity of the sensor/film to light. Here the same rule can be applied -- doubling the sensitivity (e.g. ISO 100=>200) will require twice less exposure time to get the same exposure.
It's basically as simple as this -- by changing the above settings you can influence the final exposure. From the point of view of exposure, these settings are equal and it doesn't matter if you increase e.g. ISO or exposure time. Both will result in more light reaching the sensor. As for a practical example, if on a sunny day we take a few pictures outside, and then we go inside a building, we must adapt to much less available light. We do this by changing one or more of the above settings: either increase the aperture (opening), or increase the exposure time, or increase the ISO sensitivity.
For any given lighting conditions, if for some reason (more about it in a second) you want to increase one of the parameters, you must decrease one or both other parameters accordingly. Otherwise too much light will get into the camera. Since all cameras have a built-in light meter that knows how to set the tree settings to get proper exposure, taking a picture for most people is as simple as pressing the shutter release button. The computer inside does the rest.
Now, here's where the things get exciting: the three parameters also have "side effects" -- they not only control the exposure, but also other factors very important in getting a good photo. And here's where our computer inside the camera no longer can help. Just as it's up to the photographer to choose the right point of view and composition, it should be also up to his/her vision to determine the other factors that create the final picture. Otherwise we leave this up to the computer that has absolutely no clue about our artistic vision. Here are some specifics:
Aperture
Aperture is closely connected to depth of field (DOF). Depth of field is the distance in front of and behind the object in focus, within which all objects will be sharp. Now, if we make the aperture smaller, other than letting less light into the sensor, the depth of field gets also wider. This means that for small apertures almost everything in the photo will be sharp, whether it's far away or close to the camera. Increasing the aperture will in turn make everything behind or in front of our focus point unsharp and blurry. This is great for portraits where we don't want the background to be distracting.
Using a small aperture is necessary if we want points A and B to be in focus. Large apertures will limit the DOF to the little man only.
LARGE apertures are quite strangly expressed by SMALL numbers (called F-numbers). For example taking a picture at F1.4 will have such a narrow DOF that even the ears of a person can be blurry if we focus on a person's nose (which is a bit closer to the camera). On the other hand, the aperture of F22 will let us take a picture of a person standing just in front of the camera and of the Grand Canyon far behind and everything will stay sharp.
The scale here may look quite odd, for example going from F1.4 to F2 and from F11 to F16 both mean letting in twice less light. Estimating which F-number to use to get desired depth of field comes with experience and depends on too many factors to try calculating it. Fortunately in the digital era we can take a shot, then check the result on the screen and possibly try again with another setting. An old recipe for a good photo says "F8 and be there". This is not to be taken seriously but F8 is usually a good starting point for photos of people, buildings or objects we might want to take on a walk. The background far away will be a bit blurry but still many things around the main object will stay sharp.
Exposure time
The "side effects" of this setting are much greater for photos where there is any kind of movement. A short exposure time will freeze all motion and a long one will allow taking pictures with dramatic effects or ones that tell a story with the captured movement. There is also an often undesired effect of long exposure times which is camera shake if we don't use a tripod. This is probably the single factor that ruins the largest number of photos taken if we don't pay attention to this.
There is a general rule that can be followed to know which exposure times will be too long for hand-held shots. But first we'll need to look at the idea of focal length. Even though the focal length is expressed in milimeters (it's the numbers you see on any zoom lens, e.g. 18 35 50 85...), it is better understood as the angle at which the camera looks at the world. Small or short focal lengths (e.g. 18mm or 28mm) are called wide-angle and make everything smaller than in reality because they "squeeze" objects seen at a wide range of angles into the frame. Long focal lengths are called telephoto (e.g. 135mm or 200mm) and they work like binoculars -- a very small angle at which the lens looks out at the world magnifies the objects seen, such as a small bird far away that can take up the whole frame.
Getting back to the problem of camera shake, the longest exposure time you can afford if you have relatively steady hands is 1 divided by the focal length -- in seconds. For example, if we set our zoom lens to the focal length of 50mm, we must stay under 1/50 sec to avoid blur caused by camera shake. In the telephoto range of e.g. 300mm we must take care not to exceed 1/300 sec, etc.
ISO
In the film days once we loaded a film into the camera we were stuck with a single ISO setting. Now we can change this from shot to shot. This is a great setting to have control over. If we want to carefully set exposure time and/or aperture to get a desired effect in the photo, we simply have to adjust the ISO! Unfortunately here too, there's no such thing as a free lunch. By increasing the ISO level (needed for low-light / small aperture / short exposure time situations) we also increase the noise -- it can be seen especially in the dark areas as lots of small color speckles instead of a solid color.
Naturally all three settings have their limits. In most digitals SLRs, ISO can be set between 100 and 3200, exposure time cannot be shorter than 1/8000s and possible aperture settings depend on the lens used (good quality zooms may be limited by something like F2.8 and F32). Extreme lighting conditions such as very bright days or night will often limit us to an extreme value for one or even all of the three settings. As an example, many photographers like to take photos in the city at night without a tripod and this might be only possible at ISO 3200 and F2.8 if we want to avoid camera shake.
Exposure time
The "side effects" of this setting are much greater for photos where there is any kind of movement. A short exposure time will freeze all motion and a long one will allow taking pictures with dramatic effects or ones that tell a story with the captured movement. There is also an often undesired effect of long exposure times which is camera shake if we don't use a tripod. This is probably the single factor that ruins the largest number of photos taken if we don't pay attention to this.
There is a general rule that can be followed to know which exposure times will be too long for hand-held shots. But first we'll need to look at the idea of focal length. Even though the focal length is expressed in milimeters (it's the numbers you see on any zoom lens, e.g. 18 35 50 85...), it is better understood as the angle at which the camera looks at the world. Small or short focal lengths (e.g. 18mm or 28mm) are called wide-angle and make everything smaller than in reality because they "squeeze" objects seen at a wide range of angles into the frame. Long focal lengths are called telephoto (e.g. 135mm or 200mm) and they work like binoculars -- a very small angle at which the lens looks out at the world magnifies the objects seen, such as a small bird far away that can take up the whole frame.
Getting back to the problem of camera shake, the longest exposure time you can afford if you have relatively steady hands is 1 divided by the focal length -- in seconds. For example, if we set our zoom lens to the focal length of 50mm, we must stay under 1/50 sec to avoid blur caused by camera shake. In the telephoto range of e.g. 300mm we must take care not to exceed 1/300 sec, etc.
ISO
In the film days once we loaded a film into the camera we were stuck with a single ISO setting. Now we can change this from shot to shot. This is a great setting to have control over. If we want to carefully set exposure time and/or aperture to get a desired effect in the photo, we simply have to adjust the ISO! Unfortunately here too, there's no such thing as a free lunch. By increasing the ISO level (needed for low-light / small aperture / short exposure time situations) we also increase the noise -- it can be seen especially in the dark areas as lots of small color speckles instead of a solid color.
Naturally all three settings have their limits. In most digitals SLRs, ISO can be set between 100 and 3200, exposure time cannot be shorter than 1/8000s and possible aperture settings depend on the lens used (good quality zooms may be limited by something like F2.8 and F32). Extreme lighting conditions such as very bright days or night will often limit us to an extreme value for one or even all of the three settings. As an example, many photographers like to take photos in the city at night without a tripod and this might be only possible at ISO 3200 and F2.8 if we want to avoid camera shake.
Shooting mode
As mentioned earlier, all cameras have a built-in light meter that can either tell us whether our photo will be correctly / under- / over-exposed when we use given values of the three settings. Even better, the camera can let us choose two of the settings and set the third one automatically for us to ensure correct exposure. This second functionality of the light meter is in most cases not at all limiting but instead allows us to quickly take a photo while still leaving it up to us to use a specific aperture or exposure time. This choice is controlled by the shooting mode, usually quickly adjustable from shot to shot.
Virtually all cameras offer the following shooting modes, on top of one or more automatic modes (and we do want to avoid those at all cost!):
S or T or Tv (time-priority) -- in this mode it's up to you to set the desired exposure time and ISO. The aperture will be calculated by the camera and displayed in the viewfinder / screen prior to taking the shot to let you apply changes if necessary. This mode is often used for sports photography or special effects (e.g. star trails).
A (aperture-priority) - in this mode you set the ISO and aperture and the camera will choose exposure time. Many photographers use this mode as their favorite, since you can easily control what you want to have in focus and you must only increase the ISO if the exposure time calculated by the camera is too long and introduces the risk of camera shake.
M (manual) - in this mode you control all three parameters and the camera tells you if it thinks the shot will be underexposed, overexposed or exposed correctly. This mode gives complete control over every aspect of the photo (including exposure) but is slow to use, therefore inapropriate if we need to act fast.
P (program) -- this mode is almost a fully automatic mode. You only choose the ISO and the other two settings are presented to you in pairs. Your adjustments cause a change of the aperture / exposure time pair at the same time without any preference of one setting over the other.
Prime Or Not To Prime Thats the Question
In spite of the convenience offered by zoom lenses, here are a few important reasons to switch to primes:
1. Primes are MUCH lighter and smaller. If you haven’t used primes before you should do so and you’ll see how nice they feel. This can be an important factor when hiking or walking long distances with your equipment. This brings us also to reason #2:
2. Strangers will feel much less intimidated about you taking photos of them if you use a small lens. This way you won’t look like a professional photographer (this IS good).
3. Primes are much cheaper than high-quality zooms. For example Nikon 24-70mm f2.8 will cost you around $2k bnd while primes in this range cost between $300 and $400 (50mm f1.8 will only cost $187bnd).
4. There’s no need to have all possible focal lengths. Professional photographers very often go for whole assignments with one or two primes. Also if you look at photos you take with zooms you’ll most likely notice that a majority of your photos is taken at two, may be three typical focal lengths (one will be very often at the low or high end of the range). With primes you simply zoom with your feet! If not possible (which it is in a vast majority of cases), you can always crop the photo on your computer. This is not a problem with cameras above 10MP even for large prints!
5. Quality: because of the way they’re built, primes have an amazing quality, rarely reached by zooms. Even then, a prime will always be brighter and so will give you more possibilities when shooting at night or if trying to get a low depth of field.
6. Primes are usually very well built and last forever. They have less moving parts and so will on average last longer than zooms. Focus is always lightning fast, too.
7. Primes teach you to take better photos! The need to zoom with your legs teaches you to be more creative when approaching a scene. You also learn to see with a specific focal length. This teaches you to look in ways you might not look if walking around with a zoom. This probably means you become less lazy as a photographer, I suppose.
8. If you use one or two focal lengths, your photos will not only tend to be better but will be more consistent and much nicer to look at as a whole album.
9. They are simply more fun!! but than again semua depands on the user and what they prefer and of cause your pockets...lol
Understanding Histogram
1. Primes are MUCH lighter and smaller. If you haven’t used primes before you should do so and you’ll see how nice they feel. This can be an important factor when hiking or walking long distances with your equipment. This brings us also to reason #2:
2. Strangers will feel much less intimidated about you taking photos of them if you use a small lens. This way you won’t look like a professional photographer (this IS good).
3. Primes are much cheaper than high-quality zooms. For example Nikon 24-70mm f2.8 will cost you around $2k bnd while primes in this range cost between $300 and $400 (50mm f1.8 will only cost $187bnd).
4. There’s no need to have all possible focal lengths. Professional photographers very often go for whole assignments with one or two primes. Also if you look at photos you take with zooms you’ll most likely notice that a majority of your photos is taken at two, may be three typical focal lengths (one will be very often at the low or high end of the range). With primes you simply zoom with your feet! If not possible (which it is in a vast majority of cases), you can always crop the photo on your computer. This is not a problem with cameras above 10MP even for large prints!
5. Quality: because of the way they’re built, primes have an amazing quality, rarely reached by zooms. Even then, a prime will always be brighter and so will give you more possibilities when shooting at night or if trying to get a low depth of field.
6. Primes are usually very well built and last forever. They have less moving parts and so will on average last longer than zooms. Focus is always lightning fast, too.
7. Primes teach you to take better photos! The need to zoom with your legs teaches you to be more creative when approaching a scene. You also learn to see with a specific focal length. This teaches you to look in ways you might not look if walking around with a zoom. This probably means you become less lazy as a photographer, I suppose.
8. If you use one or two focal lengths, your photos will not only tend to be better but will be more consistent and much nicer to look at as a whole album.
9. They are simply more fun!! but than again semua depands on the user and what they prefer and of cause your pockets...lol
Understanding Histogram
Understanding image histograms is probably the single most important concept to become familiar with when working with pictures from a digital camera. A histogram can tell you whether or not your image has been properly exposed, whether the lighting is harsh or flat, and what adjustments will work best. It will not only improve your skills on the computer, but as a photographer as well.
ach pixel in an image has a color which has been produced by some combination of the primary colors red, green, and blue (RGB). Each of these colors can have a brightness value ranging from 0 to 255 for a digital image with a bit depth of 8-bits. A RGB histogram results when the computer scans through each of these RGB brightness values and counts how many are at each level from 0 through 255. Other types of histograms exist, although all will have the same basic layout as the histogram example shown below.
The above image is an example which contains a very broad tonal range, with markers to illustrate where regions in the scene map to brightness levels on the histogram. This coastal scene contains very few midtones, but does have plentiful shadow and highlight regions in the lower left and upper right of the image, respectively. This translates into a histogram which has a high pixel count on both the far left and right-hand sides.
Before the photo has been taken, it is useful to assess whether or not your subject matter qualifies as high or low key. Since cameras measure reflected as opposed to incident light, they are unable to assess the absolute brightness of their subject. As a result, many cameras contain sophisticated algorithms which try to circumvent this limitation, and estimate how bright an image should be. These estimates frequently result in an image whose average brightness is placed in the midtones. This is usually acceptable, however high and low key scenes frequently require the photographer to manually adjust the exposure, relative to what the camera would do automatically. A good rule of thumb is that you will need to manually adjust the exposure whenever you want the average brightness in your image to appear brighter or darker than the midtones.
The following set of images would have resulted if I had used my camera's auto exposure setting. Note how the average pixel count is brought closer to the midtones.
Most digital cameras are better at reproducing low key scenes since they prevent any region from becoming so bright that it turns into solid white, regardless of how dark the rest of the image might become as a result. High key scenes, on the other hand, often produce images which are significantly underexposed. Fortunately, underexposure is usually more forgiving than overexposure (although this compromises your signal to noise ratio). Detail can never be recovered when a region becomes so overexposed that it becomes solid white. When this occurs the highlights are said to be "clipped" or "blown."
The histogram is a good tool for knowing whether clipping has occurred since you can readily see when the highlights are pushed to the edge of the chart. Some clipping is usually ok in regions such as specular reflections on water or metal, when the sun is included in the frame or when other bright sources of light are present. Ultimately, the amount of clipping present is up to the photographer and what they wish to convey.
Contrast can have a significant visual impact on an image by emphasizing texture, as shown in the image above. The high contrast water has deeper shadows and more pronounced highlights, creating texture which "pops" out at the viewer.
Contrast can also vary for different regions within the same image due to both subject matter and lighting. We can partition the previous image of a boat into three separate regions—each with its own distinct histogram.
The upper region contains the most contrast of all three because the image is created from light which does not first reflect off the surface of water. This produces deeper shadows underneath the boat and its ledges, and stronger highlights in the upward-facing and directly exposed areas. The middle and bottom regions are produced entirely from diffuse, reflected light and thus have lower contrast; similar to if one were taking photographs in the fog. The bottom region has more contrast than the middle—despite the smooth and monotonic blue sky—because it contains a combination of shade and more intense sunlight. Conditions in the bottom region create more pronounced highlights, but it still lacks the deep shadows of the top region. The sum of the histograms in all three regions creates the overall histogram shown before.
This section is designed to help you develop a better understanding of how luminosity and color both vary within an image, and how this translates into the relevant histogram. Although RGB histograms are the most commonly used histogram, other types are more useful for specific purposes.
The image below is shown alongside several of the other histogram types which you are likely to encounter. Move your mouse over the labels at the bottom to toggle which type of color histogram is displayed. When you change to one of the color histograms a different image will be shown. This new image is a grayscale representation of how that color's intensity is distributed throughout the image. Pay particular attention to how each color changes the brightness distribution within the image, and how the colors within each region influence this brightness.
How is a luminance histogram produced? First, each pixel is converted so that it represents a luminosity based on a weighted average of the three colors at that pixel. This weighting assumes that green represents 59% of the perceived luminosity, while the red and blue channels account for just 30% and 11%, respectively. Move your mouse over "convert to luminosity" below the example image to see what this calculation looks like when performed for for each pixel. Once all pixels have been converted into luminosity, a luminance histogram is produced by counting how many pixels are at each brightness — identical to how a histogram is produced for a single color.
The above image contains many patches of pure color. At the interior of each color patch the intensity reaches a maximum of 255, so all patches have significant color clipping and only in that color. Even though this image contains no pure white pixels, the RGB histogram shows strong clipping—so much that if this were a photograph the image would appear significantly overexposed. This is because the RGB histogram does not take into account the fact that all three colors never clip in the same place.
The luminance histogram tells an entirely different story by showing no pixels anywhere near full brightness. It also shows three distinct peaks—one for each color that has become significantly clipped. Since this image contains primarily blue, then red, then least of all green, the relative heights clearly show which color belongs where. Also note that the relative horizontal position of each peak is in accordance with the percentages used in the weighted average for calculating luminance: 59%, 30%, and 11%.
So which one is better? If we cared about color clipping, then the RGB histogram clearly warns us while the luminance histogram provides no red flags. On the other hand, the luminance histogram accurately tells us that no pixel is anywhere near full black or white. Each has its own use and should be used as a collective tool. Since most digital cameras show only a RGB histogram, just be aware of its shortcomings. As a rule of thumb, the more intense and pure the colors are in your image, the more a luminance and RGB histogram will differ. Pay careful attention when your subject contains strong shades of blue since you will rarely be able to see blue channel clipping with luminance histograms.
The petals of the red flowers caught direct sunlight, so their red color became clipped, even though the rest of the image remained within the histogram. Regions where individual color channels are clipped lose all texture caused by that particular color. However, these clipped regions may still retain some luminance texture if the other two colors have not also been clipped. Individual color clipping is often not as objectionable as when all three colors clip, although this all depends upon what you wish to convey.
RGB histograms can show if an individual color channel clips, however they do not tell you if this is due to an individual color or all three. Color histograms amplify this effect and clearly show the type of clipping. Move your mouse over the labels above to compare the luminance and RGB histograms, to view the image in terms of only a single color channel, and to view the image luminance. Notice how the intensity distribution for each color channel varies drastically in regions of nearly pure color. The strength and purity of colors within this image cause the RGB and luminance histograms to differ significantly.
TONES
The region where most of the brightness values are present is called the "tonal range." Tonal range can vary drastically from image to image, so developing an intuition for how numbers map to actual brightness values is often critical—both before and after the photo has been taken. There is no one "ideal histogram" which all images should try to mimic; histograms should merely be representative of the tonal range in the scene and what the photographer wishes to convey.| Lighting is often not as extreme as the last example. Conditions of ordinary and even lighting, when combined with a properly exposed subject, will usually produce a histogram which peaks in the centre, gradually tapering off into the shadows and highlights. With the exception of the direct sunlight reflecting off the top of the building and off some windows, the boat scene to the right is quite evenly lit. Most cameras will have no trouble automatically reproducing an image which has a histogram similar to the one shown below. |  |
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HIGH AND LOW KEY IMAGES
Although most cameras will produce midtone-centric histograms when in an automatic exposure mode, the distribution of peaks within a histogram also depends on the tonal range of the subject matter. Images where most of the tones occur in the shadows are called "low key," whereas with "high key" images most of the tones are in the highlights. |  |
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The following set of images would have resulted if I had used my camera's auto exposure setting. Note how the average pixel count is brought closer to the midtones.
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CONTRAST
A histogram can also describe the amount of contrast. Contrast is a measure of the difference in brightness between light and dark areas in a scene. Broad histograms reflect a scene with significant contrast, whereas narrow histograms reflect less contrast and may appear flat or dull. This can be caused by any combination of subject matter and lighting conditions. Photos taken in the fog will have low contrast, while those taken under strong daylight will have higher contrast. |  |
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Contrast can also vary for different regions within the same image due to both subject matter and lighting. We can partition the previous image of a boat into three separate regions—each with its own distinct histogram.
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This section is designed to help you develop a better understanding of how luminosity and color both vary within an image, and how this translates into the relevant histogram. Although RGB histograms are the most commonly used histogram, other types are more useful for specific purposes.
The image below is shown alongside several of the other histogram types which you are likely to encounter. Move your mouse over the labels at the bottom to toggle which type of color histogram is displayed. When you change to one of the color histograms a different image will be shown. This new image is a grayscale representation of how that color's intensity is distributed throughout the image. Pay particular attention to how each color changes the brightness distribution within the image, and how the colors within each region influence this brightness.
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| Choose: | RED | GREEN | BLUE | ALL | |
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LUMINANCE HISTOGRAMS
Luminance* histograms are more accurate than RGB histograms at describing the perceived brightness distribution or "luminosity" within an image. Luminosity takes into account the fact that the human eye is more sensitive to green light than red or blue light. View the above example again for each color and you will see that the green intensity levels within the image are most representative of the brightness distribution for the full color image. This also reflected by the fact that the luminance histogram also matches the green histogram more than any other color. Luminosity correctly predicts that the following stepped gradient gradually increases in lightness, whereas a simple addition of each RGB value would give the same intensity at each rectangle.| darkest |  | lightest |
*Technical Note: Strictly speaking, these should really be called "luminosity histograms." Unfortunately, the terms "luminance" and "luminosity" are often used interchangeably, including by Photoshop, even though each describes a different aspect of light intensity. Luminance refers to the absolute amount of light emitted by an object per unit area, whereas luminosity refers to the perceived brightness of that object by a human observer.
An important difference to take away from the above calculation is that while luminance histograms keep track of the location of each color pixel, RGB histograms discard this information. An RGB histogram produces three independent histograms and then adds them together, irrespective of whether or not each color came from the same pixel. To illustrate this point we will use an image which the two types of histograms interpret quite differently. |  |
The luminance histogram tells an entirely different story by showing no pixels anywhere near full brightness. It also shows three distinct peaks—one for each color that has become significantly clipped. Since this image contains primarily blue, then red, then least of all green, the relative heights clearly show which color belongs where. Also note that the relative horizontal position of each peak is in accordance with the percentages used in the weighted average for calculating luminance: 59%, 30%, and 11%.
So which one is better? If we cared about color clipping, then the RGB histogram clearly warns us while the luminance histogram provides no red flags. On the other hand, the luminance histogram accurately tells us that no pixel is anywhere near full black or white. Each has its own use and should be used as a collective tool. Since most digital cameras show only a RGB histogram, just be aware of its shortcomings. As a rule of thumb, the more intense and pure the colors are in your image, the more a luminance and RGB histogram will differ. Pay careful attention when your subject contains strong shades of blue since you will rarely be able to see blue channel clipping with luminance histograms.
COLOR HISTOGRAMS
Whereas RGB and luminance histograms use all three color channels, a color histogram describes the brightness distribution for any of these colors individually. This can be more helpful when trying to assess whether or not individual colors have been clipped.| View Channel: | RED | GREEN | BLUE | ALL | LUMINOSITY |
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| View Histogram: | RGB | LUMINOSITY | |
RGB histograms can show if an individual color channel clips, however they do not tell you if this is due to an individual color or all three. Color histograms amplify this effect and clearly show the type of clipping. Move your mouse over the labels above to compare the luminance and RGB histograms, to view the image in terms of only a single color channel, and to view the image luminance. Notice how the intensity distribution for each color channel varies drastically in regions of nearly pure color. The strength and purity of colors within this image cause the RGB and luminance histograms to differ significantly.
