Basic Photography Course

F = A

I = F G

A = F G

F = IA

G = IA

Figure 1-32.Proportional IFGA.

All image-object and focal length distance

relationship problems can be computed with the

following simple proportion:

The image size (I)

is to the image focal distance (F)

as the object size (G)

is to the object focal distance (A)

You should thoroughly understand this equation since
you will have many uses for it in many different
applications of photography.

Study the proportional IFGA figure and note the

following:

I - the image size

F - the image focal distance

G - the object size

A - the distance from lens to object

The ratio of image size to image focal distance is

the same as the ratio of object size to object focal
distance as follows:

I:F = G:A

I = F G

I = 12 x 10

3 0

The mathematical equation resulting from this

proportion is as follows:

The proportion may be written in fractional form as

follows:

When solving for I:

When solving for A:

To clear or set apart one factor of an equation so it may
be solved, divide the equation by all factors on that side
of the equation except the one to be set apart.

When solving for F:

When solving for G:

These four formulas are from the same equation
IA = FG.

Inches and feet are used in the equation that

eliminates the computations required to reduce feet
measurements to inches. However, the relation of inches
to inches and feet to feet must be maintained on the
respective sides of each equation Keep I and F values

in inches and G and A values in feet. Then, when solving
for I or F, the result will be in inches. When solving for
G or A, the result will be in feet.

In the sample problems which follow, the IA = FG

formula is used as though the camera were focused at
infinity.

PROBLEM 1: A lens with a focal length of 12 inches
is used to photograph an object 10 feet high from a
distance of 30 feet. What is the size of the image? Solve

for the unknown factor (image size) by substituting the
known factors (focal length, object size, and distance)
into the equation IA = FG. The formula and
computations are as follows:

IA=FG

I = 4, or image size equals 4 inches

l-29

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DOFMaster for Windows On-line Depth of Field Calculator DOFMaster for Mobile Devices On-line Depth of Field Table Hyperfocal Distance Chart Articles FAQ Recommended Books Support Contact Links Home As an Amazon Associate I earn from qualifying purchases.	contents <- previous page next page -> I G F = A I = F G A A = F G I F = IA G G = IA F Figure 1-32.Proportional IFGA. All image-object and focal length distance relationship problems can be computed with the following simple proportion: The image size (I) is to the image focal distance (F) as the object size (G) is to the object focal distance (A) You should thoroughly understand this equation since you will have many uses for it in many different applications of photography. Study the proportional IFGA figure and note the following: I - the image size F - the image focal distance G - the object size A - the distance from lens to object The ratio of image size to image focal distance is the same as the ratio of object size to object focal distance as follows: I:F = G:A I = F G A I = 12 x 10 3 0 The mathematical equation resulting from this proportion is as follows: The proportion may be written in fractional form as follows: When solving for I: When solving for A: To clear or set apart one factor of an equation so it may be solved, divide the equation by all factors on that side of the equation except the one to be set apart. When solving for F: When solving for G: These four formulas are from the same equation IA = FG. Inches and feet are used in the equation that eliminates the computations required to reduce feet measurements to inches. However, the relation of inches to inches and feet to feet must be maintained on the respective sides of each equation Keep I and F values in inches and G and A values in feet. Then, when solving for I or F, the result will be in inches. When solving for G or A, the result will be in feet. In the sample problems which follow, the IA = FG formula is used as though the camera were focused at infinity. PROBLEM 1: A lens with a focal length of 12 inches is used to photograph an object 10 feet high from a distance of 30 feet. What is the size of the image? Solve for the unknown factor (image size) by substituting the known factors (focal length, object size, and distance) into the equation IA = FG. The formula and computations are as follows: IA=FG I = 4, or image size equals 4 inches l-29 contents Basic Photography Course <- previous page next page ->	As an Amazon Associate I earn from qualifying purchases.
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