What F-Stop Should I Use?
This is one of the most asked questions and is the hardest to answer.
Because each subject should be treated differently and it also depends on how you want your photo to look.
How does it change the look of your photo?
F-stop or aperture changes the way your photo looks because it changes the Depth of Field (how much is in focus either side of your subject)
Some Rules of Thumb
Flat Surfaces - any f-stop will do as the flat surface has no depth.
Landscapes - usually a high f- stop (large Depth of Field) to give lots in focus.
Portrait - usually a low f - stop like f5.6 to give some blurring of the background, isolating the subject
Group Portrait - Medium DoF, f 5.6 - f11. This allows people in a 2nd or 3rd row to still be in focus and some of the background. The background in these situations is more important to give some context
Single Portraits where the background is important and part of the story f 8 - 11
Animals - same as portraits
Flowers - for an Arty Look f 2.8 - 5.6. This will give a soft look with many parts out of focus, The closer you are, the more out of focus parts there will be.
Flowers - for a true to life look - f 8 - f16. This will make most of the flower in focus. To avoid the background dominating, have a large distance from the flower to the background if possible. Alternatively, have the flower in the sun and the background in the shade.
Insects and other small creatures - same as flowers
If in doubt
Start at f 8 (compact or bridge cameras f 5.6 or in the middle of the f-stop range). Take your photo, evaluate it, if you need more in focus use a larger f stop. If you want less in focus, use a smaller f stop