1) Shutter Speed
+ On cameras adopting the traditional reflex or rangefinder design, light is usually passed through a "door" in front of the capturing media; this "door" is made up of plates that slide open when an exposure is made and then quickly closes after a certain period of time, called the shutter speed. All other things equal, slower shutter speeds let more light into the camera, producing a brighter image, while faster speeds can cause am image to appear darker. On modern compact digital cameras, the mechanical shutter is often dropped from the design since some smaller sensors can be programmed to decide when to record incoming light and transfer information out of the CCD into memory.
+ Shutter speeds are often displayed in inverted notation; that is, if your camera tells you that the shutter speed (Tv, or time value) is 1000, it probably means 1/1000 seconds, not 1000 seconds. When exposures do reach into the seconds range, tick marks (") are usually displayed beside the number.
+ Higher shutter speeds allow you to freeze movement; sports photography often calls for very high shutter speeds in order to capture movement with little or no blur.
Image taken with high shutter speed (~1/250s).+ Conversely, lower shutter speeds cause the camera to be more sensitive to movement. If you are panning your camera to the movement of a race car and want to get the streaking effect of the background, then a slower shutter speed may be appropriate. If ambient light levels are too low, you may be forced to use a slower shutter speed in order to produce a well-exposed image. Beware however, as longer exposure times may pick up the slight trembles in your hand and thus cause a blurry picture. The general rule of thumb is 1/focal length should be the slowest shutter speed to use. This of course depends on the camera type and how little your hands tremble. Rangefinder cameras, heavier than compact digital cameras but without the mirror of an SLR, tend to be the most resistant against unintended vibrations. A camera that is too small or light, or one equipped with a mirror that flips out of the way every time a picture is taken is much less resistant to these vibrations.
* Tip: To get both a blurring effect of movement and sharp rendition of the subject, you can use a flash in combination with a slow shutter speed. The brightness of the flash will freeze objects close to the camera but the slow shutter speed will blur background details. "Second curtain" flash works best for this, since the flash is fired towards the end of the exposure, leaving motion trails behind the subject.
Image taken with slow shutter speed (~1/8s) and first-curtain flash.2) Aperture
+ The aperture value (Av) is defined as the ratio between the diameter of the rear diaphragm and the focal length. Smaller values, therefore, indicate a larger diaphragm opening per a focal length. This number is often called the f-stop.
+ Larger diaphragm openings allow more light into the camera, so that the shutter speed can be raised in cases where motion blur or vibration is a concern. It also has an interesting effect of decreasing the depth of field, the amount of stuff that appears sharp and in-focus in the picture. This is because the size of the diaphragm dictates the angle at which light is bent to hit the capturing media; narrower diaphragms result in less acute angles, so objects slightly off of the focal plane may still appear sharp.
f/2,8 at 50mm
f/8,0 at 18mm+ Distance will play a role in how sharp objects close to the focal plane will appear. The closer the object, the steeper the angle that the light reflected by the subject will be captured as, resulting in less depth of field.
+ Focal length can change the appearance of blur caused by lack of depth of field. Wide angle lenses don't magnify the background details as much, so the blur due to focus also seems to be reduced. Telephoto lenses compress the scene and magnify the background so that blur is magnified by the same amount, enhancing the depth of field effect.
+ There is a trade-off of sorts between extreme aperture values and sharpness. At large diaphragm openings (small Av), the lens usually does not render fine details as well as it could at a smaller diaphragm setting due to aberrations at the outer edges of the lens. The outer edges are used with large diaphragms because of the high refraction angle. Very small diaphragm openings also reduce sharpness because light diffraction (think of light as "waves" in the case) causes interference at the plane of the capturing media. The aperture value which will produce the most amount of fine detail for any given lens will vary, but generally f/5,6-11,0 is the sharpest setting for most lenses.
+ When shopping for lenses you may notice that ones with smaller aperture values can cost exponentially more than lenses with larger values. They will also tend to weigh more and come in a much larger size. However, faster lenses don't always equate to higher picture quality, so keep this in mind before you spend $1600 on a lens that has disappointing f/1,2 picture quality.
+ Cameras with small sensors, such as the modern compact digicam, do not allow as much freedom in creative depth of field control because smaller diaphragm sizes and focal lengths are used in the lens design to project the image onto the tiny sensor.
+ The f-stop is often mistakenly used as a measurement for how much light comes through a lens, but it is technically just a ratio between the diameter of the diaphragm opening and the focal length. This means that you may get different exposures from two different lenses set at identical aperture values, shutter speeds, and sensitivities. One measurement for the amount of light coming through a lens is often called the t-stop.
3) Sensitivity
+ Often called the "ISO" setting (though in the realm of digital photography, this is hardly appropriate), this setting represents how sensitive the capturing media is to light. The higher the ISO value, the more light the sensor can capture but this at the expense of greater noise (random speckles in the picture that cannot be perceived in the original scene).
+ Higher usable sensitivities allow the photographer more control in terms of shutter speed and aperture control.
+ Digital cameras with APS-C sized sensors or larger generally have very good sensitivity, easily better than film in terms of noise response. Cameras with special sensors designed for low noise, such as Fujifilm's SuperCCD SR, are the exception to this rule and offer impressive sensitivities in a very compact package.
"ISO 800" image from a Pentax *ist DS digital SLR
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