It is so disappointing to get home from that iconic location, only to find that on your computer screen, your images are out of focus. This can happen to anyone, even advanced photographers, but there are ways to combat it. In this article I will explain depth of field*, hyperfocal distance and circle of confusion (CoC).
As we have seen in my post on aperture*, it plays a major role in determining how much of the image is in focus. As the post explains, larger f numbers (narrower apertures) have a deeper depth of field, and therefore constitute sharp images. While this does help, it is not the only option available to the more advanced photographer. The easy way out is to use infinity focus, shown on your camera as a sideways 8. This does have it drawbacks though, and another option is to calculate and use the hyperfocal distance.
This is a lot more complex. It involves the circle of confusion, and aperture, and focus distance. You can then calculate the hyperfocal distance, and achieve perfect focus from a few feet away, to infinity.
Circle of confusion is a term that often dampens the listener’s mood. It is a concept that is hard to explain, and even more so to understand. It is a measurement (a fraction of a millimetre) that is inserted into the equation used to calculate hyperfocal distance.
It works with the following fact. When we capture an image on our small sensors, and magnify them, we also magnify their faults, so say we selected on an object that was 5 m away, but instead we focused for 6 metres. There would be a slight degree of out of focus-ness which would be magnified when we print the image, or view it on a computer. The point where the CoC become visible is the point where the region concerned crosses the boundaries of the ”acceptably sharp” area, or the Depth of Field.
Hyperfocal distance is the distance at which we have to focus to achieve acceptable sharpness from near to infinity. These days technology such as iPhone have DoF calculator apps, but old lenses had a calculator on their barrel. Just set the lens to infinity and the aperture you want and you will be pointed to an appropriate hyperfocal distance. Modern lenses have unfortunately lost this feature, but DoFmaster is available online to calculate. Also, for the more mathematically minded, it is possible to use the formula below.
H= Hyperfocal distance
F= focal length
Fn= F number
The resulting number is the Hyperfocal distance, focus at that distance, and acceptable sharpness from near to infinity should be yours.
Do note, that even in the plane of focus, using the cameras smallest aperture causes softening of the image due to a large CoC thanks (or no thanks!!) to a process called diffraction*.
*Link will open in new tab.