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# Photography: 2 - Lens Sizes and Depth of Field

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A quick guide to getting more

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### Photography: 2 - Lens Sizes and Depth of Field

1. 1. Lens sizes Depth of Field
2. 2.  Camera lenses come in different sizes:
3. 3.  The longer the lens the more it enlarges the object being photographed
4. 4.  Lens are measured in mm…  50mm is roughly the same as what we see with the human eye:
5. 5.  Less than 50mm (typically 24-30mm) gives wide angles:
6. 6.  And more than 50mm (typically 70mm+) zooms in on a subject:
7. 7.  A zoom lens is a jack of all trades lens that can change its length from, say, 30mm to 70mm:
8. 8.  Many digital cameras do not have a CCD sensor that is as big as a 35mm film frame so some cropping occurs GEEKGEEK ALERT!ALERT!
9. 9.  Depth of Field (DOF) refers to how much of a photo is in focus  Suppose you have focused on a person you want to photo:
10. 10.  The DOF is the distance you could move the object towards or away from the camera without having to re-focus:
11. 11.  Everything outside of this zone will be blurred and out of focus
12. 12. >>> DEMO <<< >>>DOF with zoom lens<<<
13. 13.  There are three (four counting Photoshop) ways to create shallow Depth of Field: 1. Use a long (70mm+) lens or a zoom 2. Set a smaller aperture setting (f2.8 / f4) 3. Put a Neutral Density filter on your lens
14. 14.  There are various setting on an SLR camera:  ISO  Shutter Speed  Aperture  They all adjust different aspects of your photo…
15. 15.  Aperture adjusts the Depth of Field by changing the size of the hole that light travels through to get to your film/CCD:
16. 16.  Basically, the smaller you set the f number to, the smaller your Depth of Field:
17. 17.  Changing the aperture means changing the shutter speed to compensate (more next week), for now…  Set your camera to aperture priority mode (usually marked ‘A’ or ‘Av’on the control dial)
18. 18. Narrow DOF Wide DOF
19. 19. >>> TASK <<<  Put an a few objects on along a table  Step back as far as you can and zoom in to create DOF  Then get closer and take two identical photos – one on f2.8 and one on f16  If you don’t have these setting on your camera try using Macro mode and getting really in close…  …and/or take some photos that you can add DOF to later using Photoshop
20. 20.  On a bright summer’s day you will have to set your aperture to a high number (f11 / f16) to avoid over exposure…  So setting a small f-number to get a small Depth of Field will not work  The solution is to put a Neutral Density filter on your camera…
21. 21.  Using an ND filter is a bit like putting sunglasses on your camera
22. 22.  What this means is that you can open the aperture a bit more and get more Depth of Field  ND filters do not effect the colour, only the amount of light reaching the film/CCD
23. 23.  And, of course, Depth of Field can be faked using Photoshop selections and a blur filter:
24. 24.  >>> END <<<