Wave or particle? Light has. Wavelength Frequency Velocity

Transcription

1 Shedding Some Light

2 Wave or particle? Light has Wavelength Frequency Velocity

3 Wavelengths and Frequencies The colours of the visible light spectrum Colour Wavelength interval Frequency interval Red ~ nm ~ THz Orange ~ nm ~ THz Yellow ~ nm ~ THz Green ~ nm ~ THz Cyan ~ nm ~ THz Blue ~ nm ~ THz Violet ~ nm ~ THz 1nm is m. 1THz is 1,000,000,000,000 cycles/second

4 Velocity (the speed of light) 186,282 miles per second

5 Photons A single photon may be refracted by a lens and exhibit wave interference with itself, and it can behave as a particle with definite and finite measurable position or momentum, though not both at the same time

6 A Slinky is a photon s big brother

7 Quantity and Quality

8 What happens when light hits the sensor?

9 Colours are separated

10 Most sensors use a Bayer Filter

11 Only the right coloured light is counted in each bucket Fuji use a different pattern, the X-Trans, which is 6x6 instead of 4x4

12 Metering the Light Reflective Incident Sunny 16

13 Reflective Metering Measures the light coming off the subject Assumes the subject is neutral grey Tries to make a snowscape neutral grey Tries to make a coal cellar neutral grey It s what your camera does, either:- Spot (good for zones) Evaluative Centre weighted

14 Incident Metering Measures the light hitting the subject Gives more accurate rendering of tones (white snow or black coal) Not practical for most landscapes Enables each light in the studio to be metered separately

15 The Sunny 16 Rule On a day when there are hard shadows, the correct exposure will be about f/16 at 1/100 th of a second at ISO100

16 Manual Exposure Calculators

17 Manual Exposure Calculators

18 Levels and Histograms The buckets therefore vary between empty and full. In practice this equates to an increasing signal from the photosite. The industry has settled on counting 256 different levels of signal Empty is 0, which represents pure black Full is therefore 255, which represents pure white

19 Histograms Each vertical line represents the number of pixels of that particular brightness

20 There is no Correct histogram ISO /60 sec f/5.6 f = 200mm

21 It will vary with the image

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23 What is it for? It will show you if you have too many blacks, or too many whites. In judge-speke this means blocked up or blown out On the back of your camera this tells you if you have the exposure you want On the computer it tells you if you need to make further adjustments

24 But that s not all...

25 Ambient light: Whatever is there at the time (could be bright, could be dim)

26 Available light: Could mean the same as ambient, Could mean whatever is available, including additional sources

27 The photographer s eternal triangle

28 ISO Blacks Greys Whites

29 Benefits and disadvantages of low ISO Low ISO usually gives least noise, and the sharpest image For a given amount of light, low ISO means slower shutter speed and/or wider aperture

30 Benefits and disadvantages of high ISO Raising the ISO is effectively amplifying the signal Amplifying a weak signal means amplifying the noise too Higher ISO for a given amount of light means you can have higher shutter speed and/or smaller aperture

31 High ISO Noise ISO Under Correct Exposure Over

32 High ISO Noise ISO Under Correct Exposure Over

33 Benefits and disadvantages of high shutter speeds Faster shutter speeds eliminate camera shake Your ability to hand-hold and get acceptable sharpness depends on You, physically The focal length of the lens you are using The size of the sensor What stabilisation your camera and/or lens has Motion can be frozen (for better or worse)

34 Benefits and disadvantages of low shutter speeds Motion blur can make water and clouds much more artistic Makes Intentional Camera Movement possible Makes some form of camera support essential

35 ISO200 1/125 sec f/5.6 ISO200 1/4 sec f/13

36 Benefits and disadvantages of large apertures Allows faster shutter speed and/or lower ISO Reduced depth of field concentrates the viewer s perception Reduced depth of field means important parts of the image may be out of focus Footnote: depth of field refers to the amount of image that is in acceptably sharp focus

37 ISO 100 1/125 second f/2.8 ISO 800 1/50 second f/1.8

38 Benefits and disadvantages of small apertures Greater depth of field, can make image sharper from front to back Allows/requires a slower shutter speed which may be helpful in achieving artistic vision Slower shutter speed may give problems hand-holding Smaller apertures cause diffraction to soften the image

39 ISO 200 1/640 sec f/11

40 Stops Stops are a convenient way of thinking about exposure To double the exposure, whether by ISO, shutter speed or aperture increase by 1 stop. For example, if you want to increase shutter speed by a stop, but the exposure is already correct, you can increase ISO by a stop, or open the aperture by a stop, and the exposure will be unchanged.

41 Too simple! The f-stop relates to aperture diameter, and the amount of light admitted is proportional to the aperture area Area = πr 2 For a 1 Stop increase in aperture therefore multiply your f-number by 2 Hence the single stop range of f-numbers is 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22

42 An Answer to a Prayer? Added artificial light And/or reflect some light back into the shot

43 Artificial Light Continuous hot lights Continuous LED lights Speedlights (camera-mountable flash units) Strobes (studio type flash units)

44 Hot Lights Mains only They really are hot! Powerful Can see the light and shadow before taking the shot

45 LED Portable Colours not always stable Can be low powered Can be hard to use modifiers Can see the light and shadow before taking the shot

46 Speedlights Very portable Inexpensive (but not from Nikon and Canon!) Limited power

47 Strobes Can be mains or battery pack Depending on size/cost can be Very powerful Very adjustable Work with full range of modifiers

48 PHEW!

49 Quality of Light

50 What does quality mean? How contrasty Colour temperature Direction

51 What makes contrasty light? A single small* light source * Everything is relative: the sun is obviously enormous, but it is so far away it behaves like a point source of light

52 How to reduce contrast If you are a landscape photographer, wait for some clouds For portraits etc use A diffuser between the light and the subject Or a reflector to bounce light in from another direction Or additional light sources

53 The colour of light Early morning and late afternoon light is generally warmer Light in the middle of the day is generally cooler Reflected light can pick up the colour of the reflector

54 Direction Shadows are at least as important as light Light coming from a low angle sculpts a landscape, showing contours and features more clearly. Straight-on light makes a portrait flat and uninteresting. Lit from below a face looks ghoulish Hard, angled light is unflattering to skin

55 And now for something completely different..

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59 What s changed?

60 What s different? In the first image, the motion blur was nearly invisible In the second image it was almost too much The third image was closest to the intention

61 What s been changed? Image 1: ISO 200, 0.4 seconds f/8 Image 2: ISO 200, 0.4 seconds f/4 Image 3: ISO 200, 0.2 seconds f/4 From image 1, flash power increased 2 stops

62 0.4 seconds at f/8 0.4 seconds at f/4 0.2 seconds at f/4

63 ISO seconds at f/11

64 The Story of Blue Zoom

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66 The Inspiration!

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68 ISO seconds at f/22