Lenses

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Lenses

• By Amit Chawla

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Focal Length

• Focal length distance from the optical center
  of the lens to the focal plane (target or "chip")
  when the lens is focused at infinity. It is
  generally measured in millimeters.

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Angle of View

• It is directly associated with lens focal length.
  Longer focal length (in mm), narrower the angle
  of view (in degrees).
• When you double the focal length of a lens, you
  double the size of an image on the target and
  vice versa.

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Classification of Lenses
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Telephoto

• Taking pictures through it is like using a
  telescope - it magnifies makes everything look
  larger.
• They are having narrower angle of view and a
  longer focal length than standard lens.
• For 35mm cameras
• 70-120mm are short telephotos (often called
  portrait lenses)
• 135-210mm are moderate telephotos
• 400mm or more as extreme telephoto lenses.

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Telephoto Lens - Uses

• The main use of telephoto lenses is enabling you
  to select a small part of the subject - to pick a
  detail.
• To give greater emphasis to the subject
• To create artistic impact by getting the
  background blurred.

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Telephoto Lens Word of Caution

• Telephotos magnify camera shake as well as the
  subject, so one needs to use fast shutter speeds.
  
• The slowest speed that is recommended for use is
  1/focal length.
• With a 500mm lens, 1/500 or faster, with a
  135mm, 1/125 or faster.
• Tripod use is very imp if you need slower speeds

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Portraits (70-120 mm )

• Short telephoto lenses are especially useful for
  impressive. The working distance you need with
  them gives a natural looking perspective makes
  whole of the person's face sharp.
• 105 mm pic

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Moderates (135mm to 210 mm)

• Moderate telephoto lenses are great for picking
  out details and Isolating Subject from
  distracting material.
• You need to focus with care.
• Limited depth of field

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Extreme Tele (400 mm onwards)

• They are used for specialist purposes such as
  sports wild-life. With 35mm, a 400mm lens lets
  you stand on the boundary of a pitch and
  photograph action in the centre.
• Extreme telephotos are much easier to use when
  the action will occur in a predictable place .

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Wide Angle Lens

• A short focal length lens. For a common 35 mm
  format, a common wide angle is 28 mm.
• Wide angle lens have considerable depth of field.
  
• Show expanse
• Are useful when space in limited
• Are useful when one doesnt have time to focus
  every time

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Wide Angle Lens
v/s
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Wide Angle Lens

• Wide angle is easier are easier to work with due
  to
• Less Camera Shake
• More Depth of Field
• Everything comes in reasonable focus
• Wide angle lens is ideal for
• Landscapes Architectural photography
• For achieving distortion
• For a newness in perspective
• To catch a glimpse of interiors

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Examples of usage of Wide Angle Lens
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Examples of usage of Wide Angle Lens
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Effect of Changing LensPhotos below were taken
by 35 mm camera at constant distance from
subject.
28 mm lens 50 mm lens 70 mm
lens 210 mm lens
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Classification of Lenses

• Prime Lens Zoom Lens
• With Prime Lens, focal length of lens cannot be
  varied. Prime lenses are more predictable in
  their results. Prime lenses also come in more
  specialized forms, like, super wide angle, super
  telephoto, etc. They also give lesser distortion.

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Classification of Lenses

• Zoom Lenses came into common use in the early
  1960s. Before then, cameras used lenses of
  different focal lengths mounted on a turret on
  the front of the camera, as shown on the right.

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Classification of Lenses

• Zoom lenses use numerous glass elements, each of
  which is precisely ground, polished, positioned
  can be repositioned to change magnification of
  lens. On zoom, these lens elements move
  independently at precise speeds.

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Zoom Ratio

• Zoom ratio is conventionally used to define focal
  length range for a zoom lens. If the maximum
  range through which a particular lens can be
  zoomed is 10mm to 100mm, it's said to have a 101
  (ten-to-one) zoom ratio. But this does not shows
  that what is the minimum and maximum focal length
  of lens. A 101 zoom lens could have a 10 to
  100mm, or a 100 to 1,000mm lens, the difference
  would be quite dramatic.

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Lens Care

• Sloppy lens changing and storage is a primary
  factor that helps dust to invade camera and
  pictures.
• Cleaning of lens - occasional thorough 'scrub
  apart from regular cleaning with a dry cotton
  piece of cloth of a requirement. Using a
  specially developed brush for the same is not a
  bad idea.
• Using a UV or skylight filter.
• For as long as possible, the lens should be kept
  away from dust, smoke and moisture.