| How is an exposure made and what does the | | | | more accurate exposure. |
| camera do to make sure an image is recorded? | | | | Now if you look carefully you'll see a relationship |
| There are two parts involved in exposing film or a | | | | between f stops and shutter speeds. Each full f |
| digital sensor to light. One is the intensity of the | | | | stop either halves or doubles the amount of light |
| light and the other is the length of time the light is | | | | entering the camera and each full shutter speed |
| allowed to strike the film or sensor.Exposure= | | | | stop either halves or doubles the amount of time |
| intensity x time. Above the door in my | | | | of the exposure. Modern cameras automatically |
| photography class was this sign: E=IxT. Some | | | | do this for you. It is possible to have the same |
| students thought it meant EXIT. | | | | exposure with a variety of different f stops and |
| The f stop (aperture) is the iris in the lens that | | | | shutter speeds depending on what effect you |
| allows a measured amount of light to strike the | | | | want to achieve. If you are in aperture priority |
| film. This f stop is determined mathematically by | | | | and change the f stop the shutter speed |
| the size of the iris opening of the lens, the lenses | | | | automatically changes for a proper exposure; if |
| focal length, and the dimensions of the film or | | | | you are in shutter speed priority and change the |
| sensor. It is a factor of these three things, so the | | | | shutter speed the f stop automatically changes |
| name f (factor) stop. Each "stop" either doubles | | | | for a proper exposure. Since you don't have to |
| or halves the amount of light allowed through the | | | | manually change both factors of an exposure with |
| lens. In the old days each stop was a click on the | | | | modern cameras new photographers that have a |
| lens. You could look through the lens and see the | | | | hard time understanding this relationship. Couple |
| iris opening and closing as you rotated the dial. | | | | that with the fact that exposures are now |
| Now, most camera lenses are calibrated into | | | | broken down into thirds of a stop, trying to |
| thirds of a stop so instead of f stop numbers of | | | | explain it all seems an exercise in futility. |
| 2.8, 4, 5.6, and 8 (which are full stops) you have | | | | So I know what you are wondering, if the |
| stops like 4, 4.5, 5, 5.6, 6.3, 7.1, 8 (which divides | | | | camera automatically does this for me why |
| each stop into thirds. F 4 means that basically the | | | | should I care what my f stop or shutter speed is |
| hole on the lens is ¼ the length of the lens. | | | | and, more importantly, why did you waste my |
| F 8 means the hole in the lens is 1/8 the length of | | | | time trying to explain it? Well, knowledge is power. |
| the lens. Remember, an f stop is a factor and the | | | | Shutter speeds stop action or blur it depending on |
| bottom part of a fraction. | | | | how fast or slow of a speed you use. Aperture |
| One of the confusing parts of f stops is the | | | | controls depth of field (a property of optics that |
| larger the number the smaller the opening. If you | | | | renders sharpness to a given area). You use this |
| think... a hole that is 1/8th the length of the lens is | | | | to isolate subjects or create images that are |
| smaller than a hole that is ¼ the length of | | | | perfectly sharp throughout. If you let the camera |
| the lens. Using a plumbing analogy, a ¼ inch | | | | do everything for you you get average images |
| pipe will allow more water through it than an 1/8th | | | | and you don't learn anything. If you want to stop |
| inch pipe as long as the water pressure is the | | | | action you now know you have to use a fast |
| same. | | | | shutter speed and lose some depth of field. |
| The other part of an exposure is the amount of | | | | (Every time you use a faster shutter speed |
| time that the film is exposed. The longer the | | | | which cuts the length of time the film is exposed |
| shutter is open, the longer the light has to expose | | | | to light, you need to open up the aperture to let |
| the film, the shorter the shutter is open, the less | | | | more light in.) If you want everything in your |
| time there is to exposed the film. Where the job | | | | photograph to be sharp you know you have to |
| of the lens is to measure and focus the light the | | | | use a small aperture (high number) and you might |
| job of the camera is to open and close the | | | | have to put your camera on a tripod because |
| shutter and record the image. Just like with the | | | | you will need a slower shutter speed for a proper |
| lenses "stops" the shutter also has stops. In the | | | | exposure. (Since only a little light is being allowed |
| old days (again) each shutter speed was a click | | | | to pass through the lens you need to slow down |
| stop. Each stop was either twice as long or half | | | | the shutter speed and allow the film to be |
| as much time. Shutter speeds were like 1/30th, 1 | | | | exposed for a longer time.) |
| 60th , 1/125th, 1/250th of second. These | | | | If you want to learn how to have more control |
| represented halving the amount of light one | | | | over how your photographs turn out look in your |
| direction and doubling it the other. Modern | | | | cameras owners manual and see how to access |
| cameras shutters are now calibrated in thirds of a | | | | shooting modes and reread my article on shooting |
| stop so you have shutter speeds like 1/30, 1/40, | | | | modes to refresh your memory. Many cameras |
| 1/50, 1/60, 1/80, 1/100, and 1/125th of a second. | | | | have these shooting modes on a dial on top of |
| Now the reason both f stops and shutter speeds | | | | the camera for easy access. By accessing these |
| are broken down into thirds of a stop is to allow | | | | shooting modes you can fine tune your images |
| for a more accurate exposure. In the old days | | | | and start to improve your photography. |
| you had to fudge between the click stops for a | | | | |