1. Lenses
By: Amit Chawla

2. 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.

3. 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.

4. Classification of Lenses

5. 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)
mm are moderate telephotos
400mm or more as extreme telephoto lenses.

6. 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.

7. 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

8. Portraits ( 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

9. 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

10. 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 .

11. 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 doesn’t have time to focus every time
Wide Angle
20 – 35 mm
Super Wide
13 – 18 mm
Fish Eye
8 mm

12. Wide Angle Lens
v/s

13. 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

14. Examples of usage of Wide Angle Lens

15. Examples of usage of Wide Angle Lens

16. Effect of Changing Lens Photos below were taken by 35 mm camera at constant distance from subject.
28 mm lens mm lens
70 mm lens mm lens

17. 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.

18. 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.

19. 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.

20. 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 10:1 (ten-to-one) zoom ratio. But this does not shows that what is the minimum and maximum focal length of lens. A 10:1 zoom lens could have a 10 to 100mm, or a 100 to 1,000mm lens, & the difference would be quite dramatic.

21. 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.