Fundamental of lens in photography


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A basic view of fundamentals of lens in photography. Discusses various aspects of lens, types of lens and which lens suitable for various photography moments. Hope you find it useful

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Fundamental of lens in photography

  1. 1. Fundamentals of Lenses Anindya Das 20th October 2012
  2. 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. Weight2. Size3. Cost4. Amount of distortion
  3. 3. Important Lens Attributes Focal Length Speed Focusing Mechanism Lens Mount Image Stabilization
  4. 4. 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
  5. 5. Focal Length – Images at different focal lengths
  6. 6. Focal Length – Images at different focal lengths
  7. 7. 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”
  8. 8. Sensor conversion factor of various sizes Sensor Size App. Conversion factor Used By with reference to 35mm4/3 System 2.00 Olympus, Kodak,Panasonic, LeciaAPS-C 1.60 All Cannon DSLRs except EOS 1D and aboveDX 1.50 All Nikon DSLRs except D3 and aboveAPS-H 1.30 Cannon EOS 1D series, Leica M8Full Frame/35mm 1.00 Nikon D3 and Cannon EOS 1Dsfilm seriesFilm 6 x 4.5 cm 0.58 Pentax, Mamiya, Bronica, HasselbladFilm 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
  9. 9. 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/De.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
  10. 10. 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
  11. 11. Fast Lens – A heavy price to payLens Speed Weight (gms) Looks Like f/5.6 505 f/4.0 1,440 f/2.8 2,870 f/2.0 7,545
  12. 12. 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 finderTwo 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
  13. 13. 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 TamronFour – 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
  14. 14. 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
  15. 15. Types of LensesType Diagonal Focal Length Focal Length Type of Angle of for Full for Cropped Photography View Frame Sensors (AOV) DSLRs DSLRsUltra Wide 84 deg or 24mm or less 16mm or less Landscapes,Angle More Architecture, InteriorsModerate 62– 84 deg 24 -35 mm 16 -24 mm General purpose,Wide Angle LandscapeNormal Around 45- 40 – 50 mm 25 - 35 mm General Purpose, 50 deg Candid, Low LightShort to 12 – 28 deg 85 – 200 mm 60 – 150 mm Portraits, Candid,Medium StreetsTelephotoSuper 8 deg or 300mm or 200mm or Sports, Racing,Telephoto less greater greater Wildlife, Birds
  16. 16. 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
  17. 17. 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
  18. 18. 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
  19. 19. Zoom Lens and Prime LensZoom 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 clearestPrime 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.
  20. 20. Difference in composition at different focallengths
  21. 21. 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
  22. 22. 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.
  23. 23. 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
  24. 24. 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
  25. 25. 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
  26. 26. 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
  27. 27. 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
  28. 28. Happy Clicking