depth of Field

Depth of field is the opposite of bokeh, and tells how much of the area that is to be photographed will be in focus. With a wide aperture, that can be a very narrow sliver of space- to the point that if someone's eyes are in focus, their ears may be a little soft around the edges. The pursuit of maximum bokeh can result in a loss of focus. Using the depth of field calculator below, let's look at the same images.

Depth of field calculator
http://www.dofmaster.com/dofjs.html

Depth of field explanation
http://www.slrgeek.com/geek-speak-photography-blog/141-geek-speak-photography-blog/713-dof-depth-of-field-what-is-it.html


These photos were taken from a distance of about 2 feet from the camera to the toes using a 50mm lens at f1.7 on a dx sensor sized camera.

This yields the following results

Subject distance	2 ft
Depth of field
Near limit	1.99 ft
Far limit	2.02 ft
Total	0.03 ft
In front of subject	0.01 ft (50%)
Behind subject	0.02 ft (50%)
Hyperfocal distance	244 ft

Interpreting these results, you can see that at 2 feet, the area in focus is only from 1.99 feet to 2.02 feet, which is a very narrow range. The rest of the photo becomes out of focus, in this case intentionally. However, if a photo of someone's face were taken at this distance, if their nose was in focus, their ears likely would not be.

Hyperfocal distance is the distance that 1/2 the hyperfocal distance to infinity will be in focus. For this particular lens, that would be 122ft to infinity would be in focus.

Another thing to keep in mind is that when the area is very out of focus, it leaves a pleasing bokeh. When it is a little out of focus, it can be very distracting, and far worse than if everything were in focus.

What this and many other photography issues leads to, is that from a practical perspective, more light makes it easier to keep something in focus. At the wider apertures needed in lower light situations, less will be in focus. With longer shutter speeds in low light situations, there is a greater chance that there will be either movement from the subject of the photographer. Shooting at high ISO because of less than ideal light leads to noise in the photograph. This is one reason why lighting is so important, and you can learn to light at blogspot.Strobist.com.