The Depth of Field (DoF) increases with the distance to the subject, and even becomes infinite beyond a certain distance, which is called the hyperfocal distance. This article tells you everything you need to know about it.
We can also define the hyperfocal distance (H) as the closest focusing distance that guaranties everything behind the focus plane to be acceptably sharp. Another interesting property is that when focusing at the hyperfocal distance, the DoF extends from half the hyperfocal distance until infinite, providing the maximum DoF achievable. The awareness of hyperfocal distance is particularly useful in landscape photography when you need both foreground and background to be in focus. The pictures below gives a visual clue of what it is :
Now let’s understand how to control the hyperfocal distance. If you are at ease with formulas you do not need more explanation than this :
where - H is the hyperfocal distance - f is the focal length - A is the aperture number - c is the diameter of the circle of confusion (CoC) on the sensor
If you are more comfortable with a graph you can see below that the hyperfocal is inversely proportional to the aperture number.
And here is the same graph on a logarithmic scale, which put in evidence that the hyperfocal distance increases with the square of the focal length.
If you want to generate your own hyperfocal chart you can do it from the website http://www.dofmaster.com/charts.html
From those plot we can derive useful tips applicable to photography :
1) When you use a wide angle lens (f<24mm), any aperture will give you an hyperfocal distance of less than 10m, meaning if your subject is more than 10 meters away, any aperture provides a sufficient DoF. Good to know for landscape photography !
2) When you use a telephoto lens (f>70mm), any aperture will give you an hyperfocal distance of more than 5m, if your subject is closer than that you are likely to deal with a short DoF so pay attention to it ! This is typically the case of portrait photography.
Finally, here is a quick tip to estimate the hyperfocal distance, based on the above formula:
– On a full frame sensor (meaning CoC=0.028mm), an aperture of f/2.8 and focal length of 28mm gives you H=10m.
– On a cropped sensor (meaning CoC=0.020mm), an aperture of f/2.0 and focal length of 20mm gives you H=10m
For other values you need to do a bit of calculation knowing that it is proportional with aperture and quadratic with focal length.