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HYPERFOCAL DISTANCE
When a lens is focused at infinity, the nearest distance from the camera lens that is still in focus is called hyperfocal distance. This is true for any lens and for any given f/stop.
The practical value of this measurement is that if the lens is focused on the hyperfocal distance, everything from ½ the hyperfocal distance to infinity will be focus.
Hyperfocal distance can be calculated with the following equation:
H = Hyperfocal Distance
F = Focal Length
f = f stop
12 = conversion of inches to feet
C = Circle of Confusion (250)—the measurable gap where the light rays converge on the film plane
The Equation:
H = F2 x C
12 x f
EXAMPLE:
F = 2" ------ C = 250 ------ 12 = given ------ f = 8
Now substitute the known facts into the equation.
H = 22 x 250 H = 4 x 250 H = 1000 H = 10.4
12 x 8 96 96
The hyperfocal distance for the example is 10.4 feet. This means that when the lens is focused on infinity, the nearest object in focus will be 10.4 feet away from the camera lens.
If the photographer would focus on the Hyperfocal Distance (H.D.) which was 10.4 feet then from 5.2 feet to infinity would be in focus.
A NON-MATHEMATICAL METHOD FOR FINDING H.D.
If the camera has a depth-of-field scale on the lens it is not necessary to go through the previous above calculations; or even one of them to find the hyperfocal distance.
To find the hyperfocal distance (H.D.), simply set the lens at infinity. Each f/stop on the depth-of-field scale will have a number opposite it. This number is in feet and indicates that his number of feet is the hyperfocal distance.
To go one step farther, place the infinity mark on the f/stop you are using, read the same f/stop on the other side of the scale and this will indicate the near point in focus when you are focusing on the hyperfocal distance.
CHANGING MILLIMETERS TO INCHES
Most lenses designate their focal length in millimeters. Since the equation ask for inches, it will be necessary to change millimeters to inches. Technically there are 25.4 change millimeters to inches by dividing 25 into the number of millimeters.
For example, a 75mm lens is equal to 3 inches----- 75 = 3"
25
Another example, a 135mm lens is equal to 5.4 inches, 135
25
Practice calculating the hyperfocal distance. Select any focal length lens and f/stop and work out a problem. Do not stop at one. Do it over and over again until you thoroughly understand the process.
Check out a roll film camera and practice finding the hyperfocal distance on the depth-of-field scale. Again, repeat, repeat, repeat, until you thoroughly understand how it is done.
Do not let the four-syllable word scale you. Hyperfocal is quality of any lens that is useful when zone focusing can be used. It is most useful when it is difficult to focus for using hyperfocal distance, it is possible to cover first base, and more experience gained in photography, the greater the number of applications of hyperfocal distance that will be needed.
DEPTH OF FIELD
The photographer is nearly always concerned with getting a picture in which the principle subject matter is in sharp and clear focus. In some instances there will be subject matter both behind and in front of the subject that may also appear to be in focus. In other cases not even the entire depth of subject is in focus. The knowledgeable photographer can control the distance from the near point to the far point (depth of field) that is in focus. This is known as selective focusing or controlling the depth of field.
What is Depth of Field?
When a lens is focused on a given plane (distance), the definition (sharpness) both in front and behind the point of focus will gradually become less and less, until the lack of sharpness becomes so noticeable that the eye no longer will accept the image as being in focus. Anything behind or in front of the area of sharpness is said to be in the fuzzy zone. The distance between the nearest and farthest point of sharp focus is known as the depth of field. See the drawing below. Notice that some of the trees that are to close are out of focus and other trees that are to far away are out of focus.
The actual limit of permissible sharpness depends on what the eye is will to accept. When depth of field charts (see sample page 5) are calculated the standard of desired sharpness is determined by a measurement of the light rays as they come together (converge) at the point of focus on the film. This point is known as the circle of confusion. The measurement is used in a formula to actually determine the depth of field figures such as in the chart.
Most all cameras have a scale built on them to indicate depth of field as you focus or they may have a chart printed in the camera manual, which gives the same information. Shown on page 5 is a chart furnished with the 4x5 Graphic Press Camera. To read it simply locate the focusing distance on the left side and read over to the right under the f/stop in use. The two figures show the near and far points of focus. The difference between the two is the depth of field at that distance and f/stop.
Graflex Optar f/4.5-f/4.7, 135mm (5 ¼") lens
A circle of confusion of 2 degrees of arc (approximate 1/1720th of the focal length) has been used in computing this table. The depth-of-field values thus obtained are for critical definition and when extreme enlargements are to be made from the negatives. For most normal work, the depth of field is effectively greater.
DEPTH OF FIELD CHART
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Distance Focused On Feet |
DEPTH OF FIELD--IN FEET measured from the eptical center of the lens |
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f/4.5 - f/4.7 |
f/5.6 |
f/8 |
f/11 |
f/16 |
f/22 |
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4 |
3.9 to 4.1 |
3.9 to 4.1 |
3.9 to 4.2 |
3.8 to 4.2 |
3.7 to 4.3 |
3.6 to 4.5 |
|
5 |
4.9 to 5.1 |
4.8 to 5.2 |
4.8 to 5.3 |
4.7 to 5.4 |
4.6 to 5.5 |
4.4 to 5.8 |
|
6 |
5.8 to 6.2 |
5.8 to 6.3 |
5.7 to 6.4 |
5.6 to 6.5 |
5.4 to 6.8 |
5.2 to 7.1 |
|
8 |
7.7 to 8.4 |
7.6 to 8.5 |
7.4 to 8.7 |
7.2 to 9.0 |
6.9 to 9.5 |
6.6 to 10.2 |
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10 |
9.5 to 10.6 |
9.3 to 10.8 |
9.1 to 11.1 |
8.8 to 11.6 |
8.3 to 12.5 |
7.8 to 13.8 |
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15 |
13.8 to 16.5 |
13.5 to 16.8 |
13.0 to 17.7 |
12.4 to 19.0 |
11.5 to 21.6 |
10.6 to 25.9 |
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25 |
21.7 to 29.5 |
21.2 to 30.5 |
19.9 to 33.7 |
18.5 to 38.7 |
16.5 to 51.6 |
14.6 to 85.9 |
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50 |
38.3 to 72.0 |
36.7 to 78.7 |
32.3 to 104.3 |
29.1 to 175.8 |
24.5 to inf. |
20.6 to inf. |
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100 |
62.0 to 259.2 |
57.7 to 373.0 |
48.9 to inf. |
41.0 to inf. |
32.4 to inf. |
25.8 to inf. |
FACTORS AFFECTING DEPTH OF FIELD
In summary depth of field can be defined as: the range from the nearest point in focus to the farthest point in focus. The depth of field is controlled by the following factors:
Camera to subject distance (focusing distance)—the further the camera from the subject the greater the depth of field
Focal length of the lens (thin refers to the image producing size of the lens)—short focal length (wide-angle lenses) produce greater depth of field than long focal length lenses (telephoto).By using any of the factors above or a combination of them, the photographer can exercise control over the amount of depth of field desired. This is to say that the photographer can purposely throw foreground or background objects out of focus to suit the needs of the picture.
The intentional controlling of the depth of field is known as selective focusing. Its wise use can do much to enhance your pictures. One does not always have a different lens to use with his camera but you can almost always select from different aperture sizes and focusing distances. Study the depth of field chart and note the differing depth of fields at various distances and f/stops.
When focusing on a given distance the near point (N.P.) and far point (F.P.) of focus may be found with these formulas.
N.P. = H.D. x P.F. F.P. = H.D. x P.F. (P.F. is the point H.D. + P.F. H.D. - P.F. of focus)
When dividing if the number is negative use infinity for the answer. To find the depth of field subtract the near point from the far point.
WHAT IS IT, WHAT AFFECTS IT, AND HOW TO MAKE IT WORK FOR YOU. By Mike Laurance
When a point of light lies outside the plane of focus it will not form the image of a point at the film plane. This occurs because the light rays from this point will coverage either in front of or behind the film plane, thus forming a cone of light at the film plane. This cone is seen by the film in cross-section and is therefore recorded as a circle.
This is the circle of confusion. The closer the point is to the focused subject, the smaller the circle of confusion will be. As the point becomes farther from the focused subject, the circle becomes larger and consequently its image on the film becomes more blurred. If the circle is reproduced on the print less than for this reason, most often, .001 inch is used as the standard size for the maximum acceptable circle of confusion. What it all means is 
that if it’s less than .001 inch it looks sharp-any larger and it looks blurred.
Begin by demonstrating how the size of this circle of confusion can be manipulated by the photographer to result in greater or smaller depth of field. The basic operating principle of depth of field is proportional to the square of the camera to subject distance and is inversely proportional to the diameter of the lens aperture.
The rule states that depth of field is proportional to the square of the focused distance (camera to subject distance). In other words there would be four times the depth of field it there was twice as much distance between the camera and the subject.
Try shooting a few pictures at various distances and see just how much difference it makes. And, while you’re at that, try to learn to use the depth of field calculator on your camera. It is ironic that this handy gadget is probably the simplest yet the most misunderstood (or maybe lease used) device on a camera.
Focus the lens on any convenient object and glance at the calculator which will tell you the nearest and farthest distance from the camera that objects other than you subject will be of acceptable sharpness at a given f-stop.
Depth of field depends primarily upon two factors: the distance of the focused object from the lens and the aperture of the lens. We have already discussed how distance affects depth of field, now let’s see how aperture changes things.
About now I can imagine a few of you are wondering what happened to focal length and its effects on depth of field. After all, everyone knows that wide-angle lenses have more depth of field than long lenses. The answer to this is this: depth of field is independent of both focal length and f-number. Whoa! Don’t get so upset. Let me explain. Depth of field is dependent upon the distance between camera and subject and the aperture of the lens. This does not refer to the f-number printed on the lens, nor does it mean that focal length has no effect of depth of field.
What happens is that the aperture referred to is effective aperture and effective aperture is related to both focal length and f-number. Effective aperture is determined by using this formula:
Effective aperture (Ef) = focal length
f-number
Using that formula we find that 150mm lens at f/8 has an effective aperture of 18.75mm. Now try figuring the Ef for a 300mm lens at f/16. Aha, it also has an Ef of 18.75mm! So, the distance at which a lens focused and our already established maximum circle of confusion, you can see that the 150mm lens at the same focused distance and with the same effective aperture will yield the same depth of field.
If you followed the above in your usual perceptive manner you will have noted that the 300mm required a higher f-number to be the same effective aperture. This means, simply, that the 15 mm at f/8 has a smaller effective aperture than the 300mm at f/8 depth of field. The mathematical an optical theories are less important than their results: wider angle lenses = smaller effective apertures at given f-stops = more depth of field.
You know how to make it greater (more distance between subject and camera or smaller aperture) and how to make it smaller (less distance between camera and subject or wider aperture). You know how to find out how much depth of field you actually have (using the calculator). All that remains is for you to start making the depth of field phenomenon work for you. Use it to isolate your subject or to include more "in focus" material in you photographs. Before you shoot give some thought to depth of field-it is there, use it! Makes no difference whether you’re shooting stills or movies.