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Fundamentals of Lenses

       Anindya Das

     20th October 2012
Introduction
 Lens is one of the most important parts of the camera
 Lens is the „eye‟ of the camera and it helps to form an
  image on the sensor
 During lens design a designer have to keep the
  following in mind:
1. Weight
2. Size
3. Cost
4. Amount of distortion
Important Lens Attributes
 Focal Length

 Speed

 Focusing Mechanism

 Lens Mount

 Image Stabilization
Focal Length
 Determines the size of the image that falls on the sensor
 Longer focal length – larger size, Shorter focal length – smaller
  size
 Measured in mm – distance between the lens and the sensor
  (where image is sharply formed) when the subject is at infinity




 Photographic lens is a combination of atleast 4 elements while
  complex ones can go to more than 20.
 Multiple elements needed to correct several optical defects found
  in a single lens
Focal Length – Images at different focal lengths
Focal Length – Images at different focal lengths
Focal Length – Angle of View (AOV)

    46
    deg
    32
    deg




 A lens is qualified – telephoto or wide angle by it‟s Angle of
  View
 AOV depends on the focal length and the size of the
  sensor
 Cropped sensor gives the magnification of focal length in
  35mm times the “cropping factor”
Sensor conversion factor of various sizes
  Sensor Size     App. Conversion factor              Used By
                  with reference to 35mm
4/3 System                 2.00            Olympus, Kodak,Panasonic, Lecia
APS-C                      1.60            All Cannon DSLRs except EOS 1D
                                           and above
DX                         1.50            All Nikon DSLRs except D3 and
                                           above
APS-H                      1.30            Cannon EOS 1D series, Leica M8
Full Frame/35mm            1.00            Nikon D3 and Cannon EOS 1Ds
film                                       series
Film 6 x 4.5 cm            0.58            Pentax, Mamiya, Bronica,
                                           Hasselblad
Film 6 x 6 cm              0.51     Pentax, Mamiya, Bronica,
  Most of the super zoom equipped bridge digital cameras have
                                    Hasselblad
  very small sensors and thus need only a short focal length to
  get a great telephoto effect
Lens Speed
 It doesn‟t have anything to do with the speed of the
  subject to be photographed 
 Speed is an indication of the light gathering capacity
  of the lens
 Referred to as the “f – number” and is denoted as “f/”
 f-number denoted by f/D
e.g. if the focal length is 16 mm and the entrance pupil
  diameter is 1 mm, the f-number is 16 and the aperture
  expressed as f/16
 Lens has a “diaphragm” to control amount of light
  passing through the lens. It‟s set of blades make an
  opening called “aperture”
 Aperture size can be controlled automatic or manually
Lens Speed – “Stops”
                       Stops are in app.
                       multiples of 1.4 or √2.
                       It is bcoz each stop
                       doubles or halves the
                       area of the aperture
                       opening

                        All DSLRs give
                        “automatic diapragms”
                        which allow clear view
                        from the viewfinder
                        while composing
                        regardless of the
                        shutter speed chosen
Fast Lens – A heavy price to pay
Lens Speed    Weight (gms)   Looks Like

      f/5.6        505




      f/4.0       1,440




      f/2.8       2,870




      f/2.0       7,545
Focusing Mechanism
 Since all the objects in a composition are not
  equidistant a lens needs to be focussed
 “Heclical” focusing mechanism is used. Lens needs to
  be moved away from focal plane for near objects and
  closer for far objects
 Manual focusing done with a focusing ring and
  checking sharpness in the view finder

Two different autofocus methods:
 There is a motor in the camera which drives the lens
  through a mechanical coupling
 The body signals the motor inside the lens which does
  the needful. When the body detects the correct focus
  the driving stops
Lens Mount
 System of mechanical and electrical linkages that
  ensures proper interface between camera and lens
  body
 Propriety to each brand and cannot be changed after
  purchase
 Several independent lens manufacturers who produce
  lenses in different camera mounts e.g. Sigma and
  Tamron
Four – Thirds System
 Allows for interchange of lenses and bodies from
  different manufacturers. Standard created by Olympus
  and Kodak
 Sensor sizes are as small as crop factor of 2 (i.e. a
Image Stabilization
 Handshake adversely affects the sharpness of a picture.
    IS helps in improving the same.
   Also known as Vibration Reduction(VR) and Optical
    Stabilization(OR)
   Shake is detected by a gyroscope inside the lens and
    group of lens are moved to counteract this
   With this you can go 2-3 stops slower shutter speeds
    (e.g. if you needed 1/500s you can g upto 1/125s or
    1/60s and even get a sharp picture
   All lenses have a switch to activate/deactivate IS/VR
Types of Lenses
Type         Diagonal     Focal Length   Focal Length   Type of
             Angle of     for Full       for Cropped    Photography
             View         Frame          Sensors
             (AOV)        DSLRs          DSLRs
Ultra Wide   84 deg or    24mm or less   16mm or less   Landscapes,
Angle        More                                       Architecture,
                                                        Interiors
Moderate     62– 84 deg   24 -35 mm      16 -24 mm      General purpose,
Wide Angle                                              Landscape

Normal       Around 45-   40 – 50 mm     25 - 35 mm     General Purpose,
             50 deg                                     Candid, Low Light

Short to     12 – 28 deg 85 – 200 mm     60 – 150 mm    Portraits, Candid,
Medium                                                  Streets
Telephoto
Super        8 deg or     300mm or       200mm or       Sports, Racing,
Telephoto    less         greater        greater        Wildlife, Birds
Normal Lens
 Focal Length equal to the diagonal of the sensor frame
 Generally they are the fastest lens around and are best
  suited for low light photography
 Provide a view that is closest to the human eye
 With this you can go 2-3 stops slower shutter speeds
  (e.g. if you needed 1/500s you can g upto 1/125s or
  1/60s and even get a sharp picture
 All lenses have a switch to activate/deactivate IS/VR
Telephoto Lens
 Lenses with long focal length
 High Magnification and narrow angle of view
 Most application in wildlife, birds and sports photography
 Have an effect of compressing – distance between near
  and far looks less than reality
 Due to high magnification tendency for camera
  movement induced shake to show up very easily
 Use shutter speed of at least 1/(35mm focal length
  equivalent).    E.g. If you hold a 200mm lens on a
  cropped sensor (APS sized) then minimum speed should
  be 1/300s
Wide Angle Lens
 Shorter focal length and give wide angle of view
 They can decompress or expand the relative distance
    between objects
   Can cause some problems from perspective point of view
   Best suited for landscapes, interiors etc
   Should not be used for portraits where it will make you go
    close and you end up with some exaggerated features
    e.g. nose
   Lens will be very close to the camera body
   At very short focal lengths the lens is so close to the body
    that back of lens interferes with mirror movement
   “Retro-focus” used in wide angle lens which provides
    sufficient physical length but keeping the focal length
Zoom Lens and Prime Lens
Zoom Lens
 Lens having a range of focal length for the user to work on
 Most popular among the DSLR users
 Wider the range harder it is to keep image quality high across
  all focal lengths.
 Sweet spot in zoom lens – sharpest and clearest


Prime Lens
 Lens whose focal length cannot be changed
 Much faster than the zoom lens (e.g. 50mm f1.8). Helpful in
  low light photography
 Optics in prime lens are of way higher quality
 Much better in terms of sharpness, color reproduction,
  distortion etc.
Difference in composition at different focal
lengths
Zoom Ratio
 Number you get by dividing the longer focal length of a
  zoom lens with the shorter one is called “zoom ratio”
   E.g. for a 18-72mm zoom lens the zoom ratio is 4
 Very high ratio exist (in excess of 20). Generally such
  high ratio lenses compromise on image quality
 High zoom ratios are easy to make in small digital
  cameras but not possible for full frame sensors
   e.g. 5-90mm on bridge cameras would correspond to 28-
  500mm on full frame cameras. This will be a huge lens
  and technically challenging
Focusing and Aperture in Zoom Lens
 Parfocal Lens: Zoom lens which hold on to the focus
  when the focal length is changed. Difficult to design and
  costly to produce
 Varifocal Lens: Focus changes when you zoom. Thus
  need to focus (automatic / manual) after you zoom. Most
  commonly used technique
 Focusing is done with turning the ring on the lens where
  the focal lengths are marked.
 For P&S two way rocker switch is used to adjust focal
  length

 Lens speed changes when you zoom.
 18-70mm f/3.5 –f/5.6 is a variable aperture zoom lens.
Macro Lens
 Allows to take pictures with high magnification
 Special helical focusing mechanism which extends lens
    away from focal plane and focus very close to the subject
   Macro lens gives magnifications of >= 1:1
   Normal zoom lens produces an image as big as 1:4 on
    the sensor
   Available for range of focal lengths – 50mm to 200mm
   Higher focal length macro lenses gives a greater working
    distance
                                   1. 50 mm lens
                                   2. 300 mm mirror lens
                                   3. 300 mm lens
Fish Eye Lenses
 Extremely wide angle lens with very short focal lengths
 Circular Fish-eye: Produces 180 deg coverage all round
 and creates a circular image within the frame




 Full Frame: Diagonal AOV of 180deg and produces an
 image that covers the frame fully
Tilt and Shift Lenses
 Ability to tilt or shift a part of the lens
 Allows tremendous control over the Depth of Field
 Normally tilting a camera to include a building makes it
  look tilting backwards. Can be corrected with this lens
 Widely used in table top, architectural and landscape
  photography
 Expensive lenses. Also requires skill and understanding
Tele-Converters
 Added between the lens and the body to give longer focal
    length
   Cannot be individually used with the body
   Generally available with multiplication factors of 1.4X, 2X and
    3X
   Increase the focal length by that much factor
   Decrease the lens speed by that much factor
   Results in loss in quality as one moves up the multiplication
    factor
   Problems with autofocus. For a max aperture range of f/5.6
    tele –convertors cannot be used
   Lens with max aperture of f/4.0 convertor 1.4X can be used
    which will increase aperture to f/5.6. Hence autofocus is
    possible
So which lens is suitable for you
 Lot depends on the type of photography you do and the type
    of subjects
   For P&S zoom lens with range from 28mm to 105mm (35mm
    equivalent) will be fine in most situations
   Bridge cameras give a lot more telephoto reach
   For cropped DSLRs two lenses will be fine : Zoom of 18-
    55mm and 55-200mm . This can be covered in 18-200mm but
    will be expensive and lead to loss of image quality
   For beyond 200mm lenses image stabilization is a must
   Telephoto lenses (more than 300mm) are for very specific
    photography
   Image quality greatly depends on the lens and less on the
    body
Happy Clicking

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Fundamental of lens in photography

  • 1. Fundamentals of Lenses Anindya Das 20th October 2012
  • 2. Introduction  Lens is one of the most important parts of the camera  Lens is the „eye‟ of the camera and it helps to form an image on the sensor  During lens design a designer have to keep the following in mind: 1. Weight 2. Size 3. Cost 4. Amount of distortion
  • 3.
  • 4. Important Lens Attributes  Focal Length  Speed  Focusing Mechanism  Lens Mount  Image Stabilization
  • 5. Focal Length  Determines the size of the image that falls on the sensor  Longer focal length – larger size, Shorter focal length – smaller size  Measured in mm – distance between the lens and the sensor (where image is sharply formed) when the subject is at infinity  Photographic lens is a combination of atleast 4 elements while complex ones can go to more than 20.  Multiple elements needed to correct several optical defects found in a single lens
  • 6. Focal Length – Images at different focal lengths
  • 7. Focal Length – Images at different focal lengths
  • 8. Focal Length – Angle of View (AOV) 46 deg 32 deg  A lens is qualified – telephoto or wide angle by it‟s Angle of View  AOV depends on the focal length and the size of the sensor  Cropped sensor gives the magnification of focal length in 35mm times the “cropping factor”
  • 9. Sensor conversion factor of various sizes Sensor Size App. Conversion factor Used By with reference to 35mm 4/3 System 2.00 Olympus, Kodak,Panasonic, Lecia APS-C 1.60 All Cannon DSLRs except EOS 1D and above DX 1.50 All Nikon DSLRs except D3 and above APS-H 1.30 Cannon EOS 1D series, Leica M8 Full Frame/35mm 1.00 Nikon D3 and Cannon EOS 1Ds film series Film 6 x 4.5 cm 0.58 Pentax, Mamiya, Bronica, Hasselblad Film 6 x 6 cm 0.51 Pentax, Mamiya, Bronica, Most of the super zoom equipped bridge digital cameras have Hasselblad very small sensors and thus need only a short focal length to get a great telephoto effect
  • 10. Lens Speed  It doesn‟t have anything to do with the speed of the subject to be photographed   Speed is an indication of the light gathering capacity of the lens  Referred to as the “f – number” and is denoted as “f/”  f-number denoted by f/D e.g. if the focal length is 16 mm and the entrance pupil diameter is 1 mm, the f-number is 16 and the aperture expressed as f/16  Lens has a “diaphragm” to control amount of light passing through the lens. It‟s set of blades make an opening called “aperture”  Aperture size can be controlled automatic or manually
  • 11. Lens Speed – “Stops” Stops are in app. multiples of 1.4 or √2. It is bcoz each stop doubles or halves the area of the aperture opening All DSLRs give “automatic diapragms” which allow clear view from the viewfinder while composing regardless of the shutter speed chosen
  • 12. Fast Lens – A heavy price to pay Lens Speed Weight (gms) Looks Like f/5.6 505 f/4.0 1,440 f/2.8 2,870 f/2.0 7,545
  • 13. Focusing Mechanism  Since all the objects in a composition are not equidistant a lens needs to be focussed  “Heclical” focusing mechanism is used. Lens needs to be moved away from focal plane for near objects and closer for far objects  Manual focusing done with a focusing ring and checking sharpness in the view finder Two different autofocus methods:  There is a motor in the camera which drives the lens through a mechanical coupling  The body signals the motor inside the lens which does the needful. When the body detects the correct focus the driving stops
  • 14. Lens Mount  System of mechanical and electrical linkages that ensures proper interface between camera and lens body  Propriety to each brand and cannot be changed after purchase  Several independent lens manufacturers who produce lenses in different camera mounts e.g. Sigma and Tamron Four – Thirds System  Allows for interchange of lenses and bodies from different manufacturers. Standard created by Olympus and Kodak  Sensor sizes are as small as crop factor of 2 (i.e. a
  • 15. Image Stabilization  Handshake adversely affects the sharpness of a picture. IS helps in improving the same.  Also known as Vibration Reduction(VR) and Optical Stabilization(OR)  Shake is detected by a gyroscope inside the lens and group of lens are moved to counteract this  With this you can go 2-3 stops slower shutter speeds (e.g. if you needed 1/500s you can g upto 1/125s or 1/60s and even get a sharp picture  All lenses have a switch to activate/deactivate IS/VR
  • 16. Types of Lenses Type Diagonal Focal Length Focal Length Type of Angle of for Full for Cropped Photography View Frame Sensors (AOV) DSLRs DSLRs Ultra Wide 84 deg or 24mm or less 16mm or less Landscapes, Angle More Architecture, Interiors Moderate 62– 84 deg 24 -35 mm 16 -24 mm General purpose, Wide Angle Landscape Normal Around 45- 40 – 50 mm 25 - 35 mm General Purpose, 50 deg Candid, Low Light Short to 12 – 28 deg 85 – 200 mm 60 – 150 mm Portraits, Candid, Medium Streets Telephoto Super 8 deg or 300mm or 200mm or Sports, Racing, Telephoto less greater greater Wildlife, Birds
  • 17. Normal Lens  Focal Length equal to the diagonal of the sensor frame  Generally they are the fastest lens around and are best suited for low light photography  Provide a view that is closest to the human eye  With this you can go 2-3 stops slower shutter speeds (e.g. if you needed 1/500s you can g upto 1/125s or 1/60s and even get a sharp picture  All lenses have a switch to activate/deactivate IS/VR
  • 18. Telephoto Lens  Lenses with long focal length  High Magnification and narrow angle of view  Most application in wildlife, birds and sports photography  Have an effect of compressing – distance between near and far looks less than reality  Due to high magnification tendency for camera movement induced shake to show up very easily  Use shutter speed of at least 1/(35mm focal length equivalent). E.g. If you hold a 200mm lens on a cropped sensor (APS sized) then minimum speed should be 1/300s
  • 19. Wide Angle Lens  Shorter focal length and give wide angle of view  They can decompress or expand the relative distance between objects  Can cause some problems from perspective point of view  Best suited for landscapes, interiors etc  Should not be used for portraits where it will make you go close and you end up with some exaggerated features e.g. nose  Lens will be very close to the camera body  At very short focal lengths the lens is so close to the body that back of lens interferes with mirror movement  “Retro-focus” used in wide angle lens which provides sufficient physical length but keeping the focal length
  • 20. Zoom Lens and Prime Lens Zoom Lens  Lens having a range of focal length for the user to work on  Most popular among the DSLR users  Wider the range harder it is to keep image quality high across all focal lengths.  Sweet spot in zoom lens – sharpest and clearest Prime Lens  Lens whose focal length cannot be changed  Much faster than the zoom lens (e.g. 50mm f1.8). Helpful in low light photography  Optics in prime lens are of way higher quality  Much better in terms of sharpness, color reproduction, distortion etc.
  • 21. Difference in composition at different focal lengths
  • 22. Zoom Ratio  Number you get by dividing the longer focal length of a zoom lens with the shorter one is called “zoom ratio” E.g. for a 18-72mm zoom lens the zoom ratio is 4  Very high ratio exist (in excess of 20). Generally such high ratio lenses compromise on image quality  High zoom ratios are easy to make in small digital cameras but not possible for full frame sensors e.g. 5-90mm on bridge cameras would correspond to 28- 500mm on full frame cameras. This will be a huge lens and technically challenging
  • 23. Focusing and Aperture in Zoom Lens  Parfocal Lens: Zoom lens which hold on to the focus when the focal length is changed. Difficult to design and costly to produce  Varifocal Lens: Focus changes when you zoom. Thus need to focus (automatic / manual) after you zoom. Most commonly used technique  Focusing is done with turning the ring on the lens where the focal lengths are marked.  For P&S two way rocker switch is used to adjust focal length  Lens speed changes when you zoom.  18-70mm f/3.5 –f/5.6 is a variable aperture zoom lens.
  • 24. Macro Lens  Allows to take pictures with high magnification  Special helical focusing mechanism which extends lens away from focal plane and focus very close to the subject  Macro lens gives magnifications of >= 1:1  Normal zoom lens produces an image as big as 1:4 on the sensor  Available for range of focal lengths – 50mm to 200mm  Higher focal length macro lenses gives a greater working distance 1. 50 mm lens 2. 300 mm mirror lens 3. 300 mm lens
  • 25. Fish Eye Lenses  Extremely wide angle lens with very short focal lengths  Circular Fish-eye: Produces 180 deg coverage all round and creates a circular image within the frame  Full Frame: Diagonal AOV of 180deg and produces an image that covers the frame fully
  • 26. Tilt and Shift Lenses  Ability to tilt or shift a part of the lens  Allows tremendous control over the Depth of Field  Normally tilting a camera to include a building makes it look tilting backwards. Can be corrected with this lens  Widely used in table top, architectural and landscape photography  Expensive lenses. Also requires skill and understanding
  • 27. Tele-Converters  Added between the lens and the body to give longer focal length  Cannot be individually used with the body  Generally available with multiplication factors of 1.4X, 2X and 3X  Increase the focal length by that much factor  Decrease the lens speed by that much factor  Results in loss in quality as one moves up the multiplication factor  Problems with autofocus. For a max aperture range of f/5.6 tele –convertors cannot be used  Lens with max aperture of f/4.0 convertor 1.4X can be used which will increase aperture to f/5.6. Hence autofocus is possible
  • 28. So which lens is suitable for you  Lot depends on the type of photography you do and the type of subjects  For P&S zoom lens with range from 28mm to 105mm (35mm equivalent) will be fine in most situations  Bridge cameras give a lot more telephoto reach  For cropped DSLRs two lenses will be fine : Zoom of 18- 55mm and 55-200mm . This can be covered in 18-200mm but will be expensive and lead to loss of image quality  For beyond 200mm lenses image stabilization is a must  Telephoto lenses (more than 300mm) are for very specific photography  Image quality greatly depends on the lens and less on the body