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Exploring Photography
With modern technology, low-cost lenses
can be molded from plastic. Plastic lenses are
used mainly in inexpensive cameras.
Lens Formulas
A lens is made from a design or formula.
The formula gives:
• The type of glass
• Curvature
• Placement and spacing of the elements
Double
concave
Plano-
concave
Convexo-
concave
Figure 3-15. A negative or divergent lens is thicker at
the edges and spreads light.
Figure 3-14. A positive or convergent lens is thicker
at the center and bends light inward.
Double
convex
Plano-
convex
Concavo-
convex
Lens
Image point
Shaded area is
cross-section of lens
Film or
digital sensor
Figure 3-12. When a lens is properly designed, light rays passing through will converge, or focus, at the same
spot. Film or a digital sensor is placed at this spot called the image point.
Doublet Dialyte Triplet
Figure 3-13. A compound lens consists of two or
more simple lenses. Each simple lens is called an
element.