Exposing your pictures
First, I will define the three basic photographic terms you
will need to know. Then we can learn in greater detail
about each one.
Exposure
Exposure is the amount of light, controlled by aperture and shutter speed, that reaches the image sensor.
F-stops
F-stops are the measure of the size of the opening, or aperture, in the lens. Remember, the larger the f-stop number, the smaller the aperture. The smaller the f-stop number, the larger the aperture and the more light the lens will let through to the image sensor.
Shutter Speeds
Shutter speed is the measure of the duration or length of time that the shutter stays open. The longer the shutter stays open, the more light will be allowed to reach the
image sensor. Faster shutter speeds “freeze” the action and often require more light and a larger aperture (smaller f-stop number). Slower shutter speeds enable pictures to be taken in lower light with a smaller aperture (larger f-stop number). Before we can achieve the correct exposure it is important to know what a correctly exposed image looks like. A correctly exposed digital picture is a file that shows a full range of tones, from deep shadows to bright highlights, with detail across the entire image. You should see some detail in the dark shadow areas while at the same time retaining detail in the brighter highlight areas. Providing you get this, you can decide afterwards whether you actually need the full tonal range to appear when you print the image. If you don’t ensure that you have the full tonal range from the start, there is little you can do about it later. This last point is more crucial when shooting in JPEG format. When shooting in RAW mode, getting the right exposure is a more forgiving process than it is when you shoot color negative film because you can correct the color in your computer later.
Controlling Light
To register a fully-toned image on your digital camera sensor, you must allow the correct amount of light to reach the digital sensor. The three factors that control the path of light are sensor sensitivity (ISO), shutter speed, and aperture.
Sensor SensitivityWhen film was dominant, exposure was an incrediblyimportant subject. The digital era has brought us lightyearsforward because we can now see the result of oursettings instantly. Just as with film cameras, the D-SLRtakes into account the brightness of the subject, the contrast,the color of the picture, and the area focused. Whenset for automatic exposure, the camera calculates all thisand much more instantly. I guess you’ll have realized by now that I’m a fan of automatic exposure, providing that you review your pictures on the LCD screen on the back of your digital camera as you shoot. If you are a newcomer to photography, there are many other different aspects that have to be considered before you take each picture. How do I frame the picture? Is it in focus? What is the background like? Until all these elements start to become second nature, it’s wise to leave your camera on auto-exposure. This will give you one less thing to worry about while you concentrate on all the others. Then slowly, as you become more technically proficient and have learned to hold the camera the right way, you’ll start to appreciate the small adjustments that are possible on your camera to perfect exposure. On most D-SLRs and high-end compact digital cameras, you have the option of overriding your automatic exposure and setting the exposure manually. This is
where we begin to play with the camera’s settings. We will learn not only to expose correctly but to overexpose and underexpose eliberately. Film photography requires you to change films if you want to change the ISO setting. Digital photography, on the other hand, llows you to shoot a group of pictures, or even a single picture, at one ISO setting, then change the ISO setting on the same memory card and keep shooting. You can change the ISO as often as you like.
Shutter speedsHere are some basic tips about shutter speeds to begin:• To stop a racing car, or someone riding a bicycle, startwith 1/1000 second.• For everyday pictures such as portraits and views, usespeeds of 1/60 second to 1/250 second.• If the light is really bad, try not to go below 1/60 second.If you must, hold your camera very still and don’texpect to freeze any action
.Aperture (f-stop)
Here are some basic tips about f-stops:• As a general rule, f/5.6 gives a little bit of depth of field,provided the lens focal length isn’t too long, and is stillwide enough to enable high shutter speeds.• If it gets really dark, don’t be afraid to open your apertureto its maximum aperture, for example, f/2.• If you need loads of depth of field, or you want a slowshutter speed, stop down to f/11 (when using a shortlens) or f/16.If your picture looks a little bit lighter or darker than itshould, take another, having adjusted the exposure. Youcan make your image lighter by increasing your exposure,or darker by decreasing it.
Sensor SensitivityWhen film was dominant, exposure was an incrediblyimportant subject. The digital era has brought us lightyearsforward because we can now see the result of oursettings instantly. Just as with film cameras, the D-SLRtakes into account the brightness of the subject, the contrast,the color of the picture, and the area focused. Whenset for automatic exposure, the camera calculates all thisand much more instantly. I guess you’ll have realized by now that I’m a fan of automatic exposure, providing that you review your pictures on the LCD screen on the back of your digital camera as you shoot. If you are a newcomer to photography, there are many other different aspects that have to be considered before you take each picture. How do I frame the picture? Is it in focus? What is the background like? Until all these elements start to become second nature, it’s wise to leave your camera on auto-exposure. This will give you one less thing to worry about while you concentrate on all the others. Then slowly, as you become more technically proficient and have learned to hold the camera the right way, you’ll start to appreciate the small adjustments that are possible on your camera to perfect exposure. On most D-SLRs and high-end compact digital cameras, you have the option of overriding your automatic exposure and setting the exposure manually. This is
where we begin to play with the camera’s settings. We will learn not only to expose correctly but to overexpose and underexpose eliberately. Film photography requires you to change films if you want to change the ISO setting. Digital photography, on the other hand, llows you to shoot a group of pictures, or even a single picture, at one ISO setting, then change the ISO setting on the same memory card and keep shooting. You can change the ISO as often as you like.
Shutter speedsHere are some basic tips about shutter speeds to begin:• To stop a racing car, or someone riding a bicycle, startwith 1/1000 second.• For everyday pictures such as portraits and views, usespeeds of 1/60 second to 1/250 second.• If the light is really bad, try not to go below 1/60 second.If you must, hold your camera very still and don’texpect to freeze any action
.Aperture (f-stop)
Here are some basic tips about f-stops:• As a general rule, f/5.6 gives a little bit of depth of field,provided the lens focal length isn’t too long, and is stillwide enough to enable high shutter speeds.• If it gets really dark, don’t be afraid to open your apertureto its maximum aperture, for example, f/2.• If you need loads of depth of field, or you want a slowshutter speed, stop down to f/11 (when using a shortlens) or f/16.If your picture looks a little bit lighter or darker than itshould, take another, having adjusted the exposure. Youcan make your image lighter by increasing your exposure,or darker by decreasing it.
Exposure Compensation Setting
If you find that your images consistently look better by underexposing by one stop, or by overexposing by half a stop, then use the exposure compensation setting to build this factor into the camera’s light metering. This facility enables you to under- or overexpose by up to three f-stops or full shutter speeds. This is normally indicated on your camera by a scale from +3 to -3 with either half or third stop increments. Once you set it, the camera will usually maintain the adjustment until you change it. Most professional photographers I know use the exposure compensation feature to fine-tune the meter of their camera. Take lots of different versions of each picture. When you have time and the subject permits, vary your exposures so you don’t miss an important shot. Check the images on your computer screen and delete all the bad ones before you show anyone your work
.Automatic Exposure (AE) Modes
On most digital cameras you’ll find a variety of exposuremodes, typically referred to as:• aperture priority AE(Av)• shutter priority AE(Tv)• program AE (P)• manual (M)
Aperture Priority
The aperture priority mode enables you to set the f-stop(aperture) and the camera will then adjust the shutterspeed to give the correct exposure. This mode is particularlyuseful in low-light conditions, where you want to setthe brightest, widest f-stop in order to get the highestshutter speed and the minimum amount of movement. Ifmore depth of field is needed, you can use a small f-stopto get as much of your picture in focus as possible
Shutter Priority
Using the shutter priority mode, you can set the shutterspeed, and the camera selects the f-stop (aperture) to givethe correct exposure. This can be especially useful whenyou’re shooting action pictures and you want to freezethe motion by setting a high shutter speed. By the sametoken, if you were photographing a waterfall and youwanted the water to blur, you could set a slow shutterspeed and the aperture would adjust accordingly. It goeswithout saying that both modes assume you have enoughlight to expose your pictures within the range of shutterspeeds and apertures you’re using.
Program
This setting leaves all the decision-making to the camera.The camera sets a combination of shutter speed andaperture so you don’t have to think about exposure at all.In some cameras this may be set up as subject programssuch as “portrait,” “sports,” or “landscape.” Be carefulthough. If there’s not enough (or too much) light toachieve the effect you’re after, your camera won’t be ableto work miracles. Even on this setting, check the LCDto make sure you are getting the images you want. Andremember that you can still use autoexposure compensationto override the camera’s decision.
ManualThis mode enables you to manually set the shutter speedand the aperture independently of each other, referringeither to the camera’s built-in meter or to a handheldmeter. Professionals tend to use manual exposure andhandheld light meters. This allows them to take multiplemeter readings in various points of the subject frame. Inthis method the photographer has total control over thepictorial effects that various shutter speed and apertureIn the diagram below, each combination of lens aperture and shutter speedproduces the same exposure, or lets the same amount of light into the camera.combinations can achieve. When film was dominant, thismethod tended to be the exclusive realm of the professionalor the advanced amateur. Today, the immediatefeedback of digital photography allows you to shoot atest frame, have a look, make a slight adjustment, haveanother little look, and get your exposure right.Most advanced D-SLR cameras have an autobracket setting.This clever little feature sets the camera to take threepictures automatically, in rapid succession: one at the “correctexposure,” one overexposed, and one underexposed.I find this very useful when working quickly because Iknow it will give me a choice of exposures after the fact.By setting the camera to shoot one picture at the “correct”exposure—as the camera sees it—and two frames perhapsone f-stop either side, I’ll always end up with one framethat I consider to be the perfect exposure. You can changethe increments of the brackets so that they are 1/3, 1/2, or2/3 stop to either side of the “correct” exposure, dependingon the camera model. On most cameras this facility workson all the automatic settings and in manual mode.
