ISO, shutter speed and aperture...

Sometimes people keep asking me what is ISO or shutter speed and how do they influence the photo...

Well, I will be short on this... not to short...but I will try to keep it simple..

ISO indicates the sensitivity of the film used in the camera. Most cameras detect the coding on the film and as suchthey automaticly know what ISO value the inserted film has. This values can vary from 50, 100, 200, 400, 2000 etc. If there is a lot of light available it is desired to use a film with a lower ISO value (for example ISO 100 or 200). When darker,it is recommended to use a film with a higher ISO value, because higher value means more sensitive to light a

In a digital camera instead of a film we have the CCD's or CMOS sensor in the camera. This will influence which shutter speed to select and which diaphragm to use. For some sensors that do not support very high ISO values, when we select a high value, the image will get extremely saturated and this will result in white pixels or white areas on the picture.

Diaphragm

In every camera there is a diaphragm.A diaphragm is a mechanical part out of overlapping blades. You can adjust the diameter of the opening. If the diameter value is greater, more light will enter . This opening is indicated with the letter F.The HIGHER the number of the selected diaphragm setting the SMALLER the diameter.

So when we select an F-value f16, less light will be received then when an f8 value is set. This setting will affect the photography in combination with ISO and the shutter speed setting we choose.

Shutter speed

The shutter speed indicates how fast the diaphragm is opened and closed. We need to know this because if the image is not static and we choose a long time, the result will be a blurred image.

Now, you might ask what is the relation between those 3?

ok, let me make it clear.

Here is an example on how shutter speed can change the look of a photo

ISO 200, F4, Shutter speed 1/500

ISO 200, F4, Shutter speed 1/250

As you can observ, if the shutter speed is longer ( 1/250 >1/500) the image will be lighter ( see the sky and the persons).

Now, we have another example:

ISO 800, F5.6, Shutter speed 1/45
ISO 800, F 4.5, Shutter speed 1/20
ISO 200, F4.5, Shutter speed 1/8

So, now we can see the relationship between those 3.
Picture 1 we have a relativ normal ISO for those low light condition( value 800)and an aperture of5.6and shutter speed 1/45 sec. As you can see, the picture is not very bright. due to the great ISO number. The diaphragm is not open enough and the time that the diaphragm is open is to short.
Picture 2 we have the same ISO value of 800 but we opened the diaphragm more ( from 5.6 to 4.5) and also the time in which the diaphragm is open and lets light to get onto the sensor is greater ( from 1/45 to 1/20).
Picture 3 we have lower ISO value ( 200 ) same aperture at 4.5 but now the time is longer ( it is now 1/8 of a second ).



So that would be it for now... if you have questions, ask me.