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Exposure question

darkchild

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What does "exposure" mean? i hear people saying exposure a lot. like on the lightning pics everyone says "30 seconds exposure" or 1.3 exposure, what does that mean?
 
It means exposing the light-sensitive material for a set duration of time in order to produce an image.
 
Whenever you take a picture you are "exposing" the sensor (or film) to light. So the process of taking a picture is commonly referred to as an "exposure".

It' also is used to mean that the correct settings were used. People will say "over exposed" to mean too bright, "under exposed" to mean too dark.

*EDIT*

It means exposing the light-sensitive material for a set duration of time in order to produce an image.

Damn. You beat me to it! lol. You're fast!
 
Exposure is controlled by 3 adjustments:
  1. How big the opening (aperture) is in the lens. The bigger the opening, the more light being let in. This also controls how much of the scene, from front to back, is in focus, and is called Depth-Of-Field (DOF). Lens aperture is expressed as a fraction of the lens focal length. When the lens opening is 1/2 as wide as the lens focal length it is called f/2, the f substituting for the number 1. If the lens opening is 1/4th the lens focal length, the lens aperture is set to f/4, and so on.
  2. How long the shutter is open. The longer the shutter is open, the more time there is light to hit the image sensor (or film), for things to move and blurr because of that movement. Obviously, how long the shutter is open is not relevent for stationary objects. The shutter is usually only open for a fraction of a second in daylight, perhaps only 1/4000th of a second. Night time exposure may be for several seconds.
  3. The last part of controlling exposure is called ISO and is a measure of how sensitive the image sensor (or film) is to light. In bright daylight, low ISO values (100) are used, at night high ISO values are used (6400).
 
ok so what does "30 second exposure" mean?
 
:madmad: :puke: :banghead: :gah:
 
ok so what does "30 second exposure" mean?


It doesn't say anything about how sensitive to light the camera is, it just says the shutter was open for 30 seconds.

In a 30 second exposure, anything that moves while the shutter is open will be blurred. A 30 second exposure is usually only used when there is very little light getting to the image sensor (or film).

Any comment about exposure that deals with time - means they are talking about shutter speed. Comments about aperture or f-stops, are about the size of the lens opening. Comments about ISO, are about the image sensor (or film) sensitivity to light.

You may hear someone say to add or subtract a 'stop' of exposure. A doubleing of an exposure value, be it shutter speed, lens aperture, or ISO is adding a 'stop'. A halving of an exposure value, be it shutter speed, lens aperture, or ISO is subtracting a 'stop'.

In the case of lens aperture, a doubleing or halving is refering to the area of the lens opening, not the diameter. As a consequence f-stop numbers are a function of the square root of 2: √2.
 
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