Practicing Photography? kinda interesting. I am using my semi SLR Sony NEX3
Here's How? from:
http://silverlight.co.uk/tutorials/compose_expose/exposure1.html
I know, and I am sorry but there is more. Now that you know what a
'stop' is you may realize that to change or control exposure you can
alter either one and get the same effect. You may even have worked out
that you can have loads of combinations of aperture and shutter speeds
that will amount to the same exposure.
Here is a wee example:
Your light meter tells you to set your camera to f-8 at 1/125th of a
second. You decide that you want to change it. You will find out why you
might want to change it later.
You could reduce the aperture by one stop to f-11 (Stop down or close
down). Now your film is receiving half as much light as it requires
(underexposure). To compensate for this you select a slower shutter
speed of 1/60th of a second so it now stays open twice as long as before
and passes twice as much light as before.
Or.
You could increase the aperture by one stop to f-5.6 (Open up). Now your
film is receiving twice as much light as it requires (overexposure ).
To compensate for this you increase your shutter speed to 1/250th of a
second so it now stays open for half as long as before and passes half
as much light as before.
| f-32 |
1/8th of a second |
| f-22 |
1/15th of a second |
| f-16 |
1/30th of a second |
| f-11 |
1/60th of a second |
| f-8 |
1/125th of a second |
| f-5.6 |
1/250th of a second |
| f-4 |
1/500th of a second |
| f-2.8 |
1/1000th of a second |
| f-2 |
1/2000th of a second |
Alternatively, you could start by changing the shutter speed
then altering the aperture to compensate. The important point is that
you finish up getting the same exposure.
You could work your way through the whole range of aperture and shutter speeds as in the table on the right:
When you combine a shutter speed and an aperture you get an 'Exposure
Value (EV)'. The table shows a range of shutter and aperture
combinations which will all result in the same exposure value. If an
aperture of f-8 at 1/125th of a second produces a perfectly exposed
photograph then any of the other combinations will do the same.
Film speed
Here is something else just to confuse you.
In order for your lightmeter to come up with a suitable combination of
aperture size and shutter speed it needs to know how sensitive to light a
particular film is. A film's sensitivity is known as its ' speed' and
is expressed as an ASA/ISO number. The higher the number the more
sensitive it is and consequently the less light it needs to form an
image. The lower the number the less sensitive it is and the more light
it will require. Sensitive films are said to be 'fast' and will have a
speed of 400 ASA/ISO or above. Films with low sensitivity are said to be
'slow' and will have a speed of less than 100 ASA/ISO. General purpose
films suitable for everyday use fall into the 100-400 ASA/ISO range
with 100-200 being the most popular.
Like shutter speeds and aperture sizes, film speeds follow a standard sequence.
25; 50; 100; 200; 400; 800; 1600; 3200
Wouldn't you know it ! Film speed goes up in steps just like shutters
and apertures. Each one is twice as sensitive as the next. I know you
have worked this out already but the difference between one film speed
and the next is a 'stop'.
As far as exposure goes all you really need to know about film is its
speed. It is very important that you set the correct film speed on your
light meter before you start. Most modern cameras read the film speed
from a magnetic strip on the film cassette and set the meter accordingly
(DX coding). Otherwise you will have to set it yourself using whatever
method your camera/meter is equipped with.
The outcome of Photo:
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| These are my daily routine gadgets & use. |