It's really very simple...

Started Sep 15, 2011 | Discussions thread
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olyflyer
olyflyer Forum Pro • Posts: 23,953
It's really very simple...

Four simple rules of photography:

1. Set the aperture to get the desired DOF.
2. Set the shutter speed to get the desired shutter speed.
3. Set the ISO to create the exposure according to the above.
4. Use the lens which is giving you the angle of view you want.

Why am I starting a thread about this? Because in several posts I have just recently read about a very common misunderstanding about focal length. Some people say that if you want narrow DOF you have to use a longer focal length. This is simply not true. The DOF will remain the same, regardless of focal length, if the aperture is the same and the framed image is the same. The basic message is that zooming with your feet and using a longer focal length won't give you narrower DOF but a different angle of view. You will of course get narrower DOF using a longer lens if you are standing on the same spot, but then you will not get the same frame. The only way to get shallower DOF is if you use a larger aperture opening, or of course, if you use a camera with larger sensor.

In other words, the four simple rules are:

Aperture is used for controlling the DOF.
Shutter speed is used for freezing motion (camera or subject).
ISO is used for controlling the exposure.
Focal length is used for controlling the angle of view only.

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