Optomath: Photographic Equations

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35mm Focal Length Multiplier

mf35 = d35 / di = √(362 + 242) / di =  √1872 / di

where:
mf35 is the 35mm focal length multiplier
d35 is the diagonal of the 35mm (135) format, mm
di is the diagonal of the initial image, mm

35mm Equivalent Focal Length

f35 = fi * mf35

where:
f35 is the 35mm equivalent focal length, mm
fi is the initial focal length, mm
mf35 is the 35mm focal length multiplier

Circle of Confusion

c = d / x

where:
c is the circle of confusion, mm
d is the image diagonal, mm
x is the divisor

divisors:
1500 (used by Zeiss, we recommend)
1730 (used by Leica)
1300 (used by Nikon)

On the web you’ll found many site says d/1730 is the “Zeiss Formula”, but that’s a bullshit.
Read the official Zeiss publication about depth of field & circle of confusion on page 3 here.

Depth of Field Equations

Hyperfocal distance, near distance of acceptable sharpness, and far distance of acceptable sharpness are calculated using the following equations (from Greenleaf, Allen R., Photographic Optics, The MacMillan Company, New York, 1950, pp. 25-27):

Hyperfocal distance:

hyperfocal2

Near distance of acceptable sharpness:

neardistance2

Far distance of acceptable sharpness:

fardistance2

where:
H is the hyperfocal distance, mm
f is the lens focal length, mm
s is the focus distance, mm
Dn is the near distance of acceptable sharpness, mm
Df is the far distance of acceptable sharpness, mm
N is the f-number, f-stop
c is the circle of confusion, mm

f-number is calculated by the definition N = 2i/2 , where i = 1, 2, 3,… for f/1.4, f/2, f/2.8,…

Calculations using these equations must use consistent units. When focal length and circle of confusion have units of millimeters, the calculated hyperfocal distance will have units of millimeters.

To convert to feet, divide H by 304.8. To convert to meters, divide H by 1000.

Angle of View (Field of View)

α = 2*arctan(d/2f) * (180/Pi)

where:
α is the angle of view, degree
d is the image diagonal, mm
f is the focal length, mm

this formula gives results in degrees.

This formula presumes lenses without distortion. These calculations don’t apply to fisheye lenses.
Different fisheyes use different projections, so different formulas apply to different fisheye lenses.


source 1, source 2

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