Exposure explained

To get the correct exposure when you take a picture, you have to get the exact amount of light to your sensor.  I mean exact.

There are three elements that control the amount of light that you need for your picture and how much actually gets there.

ISO

I am going to start with the sensor.  In the old film cameras, that was the film.  When people bought film, they bought ISO 50,  100, 200, 400 or 800 and others  and the higher the number, the higher the sensitivity.  In other words, the higher the number, the less light was needed to create the picture.  Now we dial in the ISO that we want and we don’t have to wait until the film runs out to change it.   
With film and with digital, when you use a higher ISO you tend to lose quality in your pictures.

Shutter speed

The shutter speed is just that.  How fast the shutter opens to let the light in.  You can set it so that you open it yourself and close it when you want to.  That would be for night shots, fireworks or lightening.  Most of the time you would use the regular shutter speeds from 1 second to 1/8000 of a second (on some cameras).

Aperture or f-stop

This is the lens diaphragm opening inside of your lens. When you set you aperture to f-22 the opening is very small and when you set it to f-4 the opening is very big.  Obviously, the bigger the opening the more light gets in. The picture at the top is an actual picture of lens with the f-stops.

Let’s put it all together.

If you put your camera onto the manual setting you need to set everything together so that the exact amount of light hits the sensor.  When your ISO is small you will need more light, so slower shutter speeds and larger openings with your f-stop.  If you increase the ISO, you will need to take away some light.

Whenever you increase the speed of your shutter (shutter speed) you will have to let in more light through the lens and open up the f-stop  (closer to the side with f-4).


They all work together, if you already have the perfect light and you change one of them, you will have to change at least one other one.  Most people either change the shutter speed or the aperture.


If you have a camera that has a manual mode, go and play with the setting and see what you can come up with.  Whatever you do, you can always put it back into the program mode.