In the previous entry about hyperfocal distance, I introduced several mathematical relationships that make all of this work. Simply put, using the hyperfocal distance (HFD) at any given aperture, will produce the greatest depth of field (*). By looking at some examples across different sensors (full frame and 1.5 crop factor) you can get an ideal of just how beneficial this information can be and how you can use it to your advantage.
Let’s quickly contrast the impact of a full frame vs a 1.5 crop factor sensor across two focus settings to see the relationship. Using a Nikon D3, 14mm focal length, f4 aperture, and object focus distances of 5 and 15 feet will return a zone of focus of 2.6ft (near) to 66.2 ft (far) and 3-9ft (near) to infinity (far), respectively.
The same settings on a Nikon D300 will yield a zone of focus of 3ft to 13 ft and 5.25 to infinity for focus points of 5 and 15 ft respectively. Comparing the closer focus points across the two sensors, the full frame sensor will generate a greater depth of field.
A practical use of the HFD is to determine where to set your focus point to achieve the maximum depth of field. Photographing in the sand dunes of Namibia, I wanted as much DOF as possible. Using the HFD tables, I determined that a 14mm lens set f8 with a focus point of 5ft would return a depth of field of 1.76 ft to infinity. Armed with this data, I simply manually set the focus at 5 ft and fired away, never touching the focus again (as long as I did not change the focal length).
I have found that using HFD information on wide angle lenses returns more images that are in focus than before. Having said this, HFD is not something I use all the time, so learn when to use it and it will make a difference.
In the next and final entry on HFD, I will explore the HFD tables in more detail and several iPOD applications that make all of this easy.
* New York School of Photography
Cheers, Happy Holidays and happy photo’ing