FP_LESSON 11

Prepared by: CAM Gonzales

LENSES

What is Lens?

A lens is an image-forming device that significantly impacts image quality. It's a medium that converges or diverges light rays to create an image, often made of transparent material (like glass) that allows light to pass through while altering its direction

It is also a transparent material with curved surfaces that is used to refract or bend light. It is commonly used in eyeglasses, cameras, magnifying glass, and telescopes to focus and manipulate light.

Daniel Barbaro – first to introduce the use of lens in the camera.

CLASSIFICATION OF LENS

A. ACCORDING TO THE TYPE OF IMAGE TO BE PRODUCED

CONVEX LENS

A convex lens (also called a converging lens or positive lens) is thicker at its center than at its edges. This shape causes light rays passing through it to bend inward and converge at a point, creating a real, inverted image.

For example, a magnifying glass is a convex lens; when you use it to focus sunlight, the inverted image of the sun is projected onto a surface.

CONCAVE LENS

A concave lens (also called a diverging lens or negative lens) is thinner at its center than at its edges. This shape causes parallel light rays passing through it to spread out (diverge), forming a virtual, upright, and reduced image on the same side of the lens as the object.

For example, the lens in a peephole viewer is often a concave lens; it provides a wider field of view but creates a smaller, upright image.

B. ACCORDING TO THE DEGREE OF CORRECTIONS

MENISCUS LENS

A simple lens with no correction for inherent optical defects like distortion or aberration. It's a basic lens shape, often used as a starting point in more complex lens designs.

Example: A very basic, inexpensive magnifying glass might utilize a simple meniscus lens.

RAPID RECTILINEAR LENS

A lens designed to correct distortion, resulting in straighter lines in the image, particularly at the edges.

Example: Early photographic lenses aimed at architectural photography often employed this design to minimize the distortion of buildings.

ANASTIGMAT LENS

An anastigmat lens is a camera lens designed to minimize three common image defects: astigmatism (blurring of lines at different angles), coma (hazy, comet-shaped blurring of point light sources), and spherical aberration (blurring caused by the lens's curvature). This results in sharper, clearer images across the entire field of view. Many modern camera lenses, from wide-angle to telephoto, incorporate anastigmat designs to improve image quality.

ACHROMATIC LENS

A lens designed to minimize chromatic aberration, a color fringing effect caused by the different wavelengths of light bending at different angles. Example: Telescope eyepieces often use achromatic lenses to produce sharper, less color-fringed images of celestial objects.

APOCHROMATIC LENS

An apochromatic lens is a high-performance lens designed to bring all colors of light into sharp focus at the same point, thereby eliminating chromatic aberration (color fringing) and minimizing spherical aberration (blurriness due to lens curvature). This results in exceptionally clear and detailed images. For example, high-end telephoto lenses used in professional photography and advanced microscope objectives often utilize apochromatic designs.

LENS DEFECTS

SPHERICAL ABERRATION

The edges of the picture are blurry because the lens doesn't focus all the light rays to the same point.

COMA

Off-center objects appear blurry and stretched out like comets.

CURVATURE OF FIELD ABERRATION

The image is sharp only in one plane; other parts are out of focus.

DISTORTION

Straight lines appear bent; either bulging outward (barrel distortion) or inward (pincushion distortion).

CHROMATIC ABERRATION

Color fringes appear around edges because different colors of light focus at slightly different points.

ASTIGMATISM

Horizontal and vertical lines are blurry because the lens doesn't focus them equally.

FLARES

Extra, unwanted images appear due to internal reflections within the lens.

LENS CHARACTERISTICS

What is Lens Characteristics?

Lens characteristics describe the properties and qualities of a lens that affect how it forms an image. These characteristics are important for understanding how a lens performs and for selecting the right lens for a specific application.

Two (2) Characteristics of Lens:

Focal Length: This is the distance between the lens's optical center and the point where parallel light rays converge after passing through the lens. It determines the magnification and field of view of the lens. A shorter focal length creates a wider field of view and a wider angle of view.

Normal Lens, Wide-angle and telephoto lenses represent three distinct categories based on their focal length.

Aperture: This is the light gathering power of the lens expressed in F-number. This is the size of the opening in the lens that controls the amount of light passing through it. It is measured in f-stops (e.g., f/2.8, f/8). A larger aperture (smaller f-stop number) allows more light to enter the lens, creating a brighter image and shallower depth of field.

Aperture settings directly influence two key photographic elements: depth of field and hyperfocal distance.

CLASSIFICATION OF LENSES ACCORDING TO ITS FOCAL LENGTH

WIDE-ANGLE LENS

Wide-angle lenses have short focal lengths, resulting in a wide field of view, ideal for capturing expansive scenes or fitting more into a frame at close range. Examples include 16mm, 24mm, and 28mm lenses.

NORMAL LENS

Normal lenses have a focal length approximating the diagonal of the sensor (e.g., around 50mm for a full-frame camera), providing a perspective similar to human vision

TELEPHOTO LENS

Telephoto lenses possess long focal lengths, magnifying distant subjects and compressing perspective. Examples include 70-200mm and 100-400mm lenses

ZOOM LENS

Zoom lenses offer a variable focal length, allowing the photographer to adjust the field of view and magnification without changing lenses.

KEY IMPORTANT CONCEPTS UNDER APERTURE

DEPTH OF FIELD

Depth of field refers to the area in an image that appears acceptably sharp, extending from the nearest to the farthest in-focus point. A wide aperture (low f-number) produces a shallow depth of field, blurring the background, while a narrow aperture (high f-number) yields a large depth of field, keeping both foreground and background sharp.

HYPERFOCAL DISTANCE

Hyperfocal distance is the focusing distance that maximizes depth of field, resulting in the sharpest image from a specific point to infinity. For example, setting your lens to its hyperfocal distance for landscape photography ensures maximum sharpness from the foreground to the distant horizon.

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