Optimal Aperture For Large DOF 10-70mm
A common problem with landscape photography is "how do I make both the foreground and the distance look sharp at the same time"?
Where to focus
A foreground object and a distant background object are equally sharp when you focus twice as far away as the foreground object. For example, if there is a tree 1m away from you, you should focus at a point 2m away from you to render detail on the tree as sharply as details in the far distance.
What aperture to use
Wide apertures cause objects that aren't at the focus distance to become blurry (due to the Circle of Confusion). Small apertures cause the whole image to become more blurry (due to diffraction). This graph shows the best compromise between the two.
Returning to the tree example: if you were to focus at 2m using an 18mm lens, the graph shows that an aperture of f/16 would give you the sharpest detail on the tree and details in the far distance.
How the graph was calculated
The lines are drawn though points where the Circle of Confusion is the same size as the Airy Disc. The relationship holds whatever sensor size your camera has - no conversion factor is necessary (you should use actual focal lengths to read this graph, not 35mm equivalents).
Some useful conclusions
Short focal length lenses give sharp results with wide apertures, and so perform well hand-held. Long focal length lenses work best with small apertures, and so should be tripod mounted. When focusing on objects close to, you'll need to use a small aperture to keep the distance sharp. If you focus on distant objects, you can use a wider aperture. Cameras that use short focal lengths, such as digital compacts, give the sharpest results at wide apertures. Cameras that use long focal lengths, such as medium format cameras, give the sharpest results at small apertures.
Also see the 10-30mm graph
Optimal Aperture For Large DOF 10-70mm
A common problem with landscape photography is "how do I make both the foreground and the distance look sharp at the same time"?
Where to focus
A foreground object and a distant background object are equally sharp when you focus twice as far away as the foreground object. For example, if there is a tree 1m away from you, you should focus at a point 2m away from you to render detail on the tree as sharply as details in the far distance.
What aperture to use
Wide apertures cause objects that aren't at the focus distance to become blurry (due to the Circle of Confusion). Small apertures cause the whole image to become more blurry (due to diffraction). This graph shows the best compromise between the two.
Returning to the tree example: if you were to focus at 2m using an 18mm lens, the graph shows that an aperture of f/16 would give you the sharpest detail on the tree and details in the far distance.
How the graph was calculated
The lines are drawn though points where the Circle of Confusion is the same size as the Airy Disc. The relationship holds whatever sensor size your camera has - no conversion factor is necessary (you should use actual focal lengths to read this graph, not 35mm equivalents).
Some useful conclusions
Short focal length lenses give sharp results with wide apertures, and so perform well hand-held. Long focal length lenses work best with small apertures, and so should be tripod mounted. When focusing on objects close to, you'll need to use a small aperture to keep the distance sharp. If you focus on distant objects, you can use a wider aperture. Cameras that use short focal lengths, such as digital compacts, give the sharpest results at wide apertures. Cameras that use long focal lengths, such as medium format cameras, give the sharpest results at small apertures.
Also see the 10-30mm graph