Monday, March 21, 2011

Keeping it all in focus


Hyperfocal example: Staircase in tunnel - Rock City, Tennessee (TN)
Hyperfocal example:
Staircase in tunnel -
Rock City, Tennessee (TN)
Often times, when taking travel photographs, we are faced with interesting foreground, middle-ground and background subjects and we want all of them reasonably in focus. To gain the maximum depth-of-field (DoF) and achieve our goal we have basically two options: Stop the lens all the way down or set the hyperfocal distance that is optimal for your subject distances.
Hyperfocal example: Walkway and cliff face - Rock City, Tennessee (TN)
Hyperfocal example:
Walkway and cliff face -
Rock City, Tennessee (TN)
Before we get into the details lets define "depth-of-field" as simply what is in focus beyond the point of focus (PoF). Typically this is 1/3 in front of the point of focus and 2/3 behind the point of focus. There are a lot of factors that go into DoF including image format (size), focal length and subject magnification. To fully flush out all these factors would be a very lengthy article. So in the interest of conciseness and simplicity we’ll stick to our simple definition.
Stopping down the lens
The first of these options, stopping the lens all the way down, is least desirable. Without getting overly technical it’s sufficient to say that, due to laws of physics relating to light refraction, stopping all the way down actually makes the overall image less sharp while adding DoF. For better results lets explore the concept of "hyperfocal distance."
Hyperfocal distance
Hyperfocal distance is defined as "... the closest distance at which a lens can be focused while keeping objects at infinity acceptably sharp; that is, the focus distance with the maximum depth of field. When the lens is focused at this distance, all objects at distances from half of the hyperfocal distance out to infinity will be acceptably sharp."
The good news is that the technique is simple to employ. Basically what needs to be kept in mind is finding the f-stop which provides optimal performance for your lens. In my experience any wide-angle lens from 21mm to 35mm (35mm format equivalent) performs best somewhere between f/8 and f/11 when setting for hyperfocal distance. Once you’ve determined the best setting for your lens, using the following technique, you can use that f-stop reliably ... confident that you will get the results you are after.
Technique 1
Hyperfocal setting of Mamiya 7 43mm lens (21mm in 35mm equivalent). With infinity set at f/11 the depth-of-field is from about 4.5 feet to infinity.
Example 1
Hyperfocal setting of Mamiya 7 43mm f/4.5 lens (21mm in 35mm equivalent). With infinity set at f/11 the depth-of-field is from about 4.5 feet to infinity.
The simplest version of this technique (Example 1) is to set your infinity mark on your lens next to the f-stop mark you’ve determined to be correct (in this case, f/11). Looking at the f-stop mark on the opposite side of the focus line will tell you the distance at which foreground subjects will be in focus (approx. 4.5 feet). Just this simple setting maximizes your DoF. Now compose your image and take the photo.
Technique 2
Hyperfocal setting of Mamiya 7 43mm lens (21mm in 35mm equivalent). With focus set at about 4.5 feet the depth-of-field is from about 3 feet to 8 feet.
Mamiya 743mm f/4.5 lens (21mm in 35mm equivalent) with focus set at about 4.5 feet. At this setting the depth-of-field is from about 3 feet to 8 feet ... much shallower than the hyperfocal setting in Example 1.
The second version of this technique is not much more complicated it just allows you to be more selective in determining your foreground subject. Use Technique 1 described above to determine the distance at which your foreground subjects will be in focus. Then set the focus to that point (approx. 4.5 feet in our example). Next physically move so that your foreground subject is at that distance or just slightly beyond that distance. Now reset your hyperfocal distance as described in Technique 1. Lastly, compose your image and take the photo.
The main difference between these two techniques is simply that you are making sure that your forground subject falls within the hyperfocal distance. If your camera has a DoF preview function you can use that to aid in checking what will be relatively in focus in your image.
Using this simple technique will maximize your DoF without sacrificing overall image sharpness. Obviously there are times when you want to assure that a certain subject in the scene is absolutely in focus. During those instances, forgo the hyperfocal technique and focus accurately on your subject.
Originally published in The Beacon Newsmagazine September 2010
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