Using Depth of Field
Most of us know by now the principals of Depth of Field - Large number f-stop eg f16, gives a large depth of Field and a small numbered f-stop eg f4 gives a shallow Depth of Field. But when do you use them?
The classic example is the difference between landscapes and portraits.
Landscapes - you want a large DoF because you want a lot in sharp focus - so you use f 16 or similar. See Infra Red photo above.
Portraits - particularly for head and shoulder shots, you want to separate the person from the background so a shallow DoF so you use f4
But - if you want to use the background behind the person as part of the image for context - then you may need to use a larger DoF like f 5.6 or f8. Not too large though, because if you are using the background you are more likely to be further away, so the DoF for the same f-stop will be larger!
Confused yet? Try this one.
For Macro shots you often want a blurred background, so you use a low f-stop right? Wrong! You use a very high f-stop!
Why? because the closer you are to a subject the smaller the DoF for a given f-stop. Also the longer the lens the smaller the DoF for a given f-stop. So for Macro shots of tiny subjects, often the DoF is only millimetres in length. This means that your focus must be critically sharp and on the right spot.
What about photos of grasses? There are 2 shots below - 1 has a an f-stop of 2.8 and the image is soft and arty. The other has an f-stop of f8 and shows the grass heads in detail. Both are good photos, they just show different things.
There is no right and wrong with Depth of Field. It is up to the person taking the image to decide what he wants to show and how much is sharply in focus. If it looks right and it tells the story you wish to show - then it is right.
Still confused about when to use which one? There are a few classes that will help - Making it Work - Depth of Field in Detail- which is running in August and the Level 3 lessons on Composition.
In the meanwhile try different f-stops and see what happens
