Photography Basics. Exposure

Transcription

1 Photography Basics Exposure

2 Impact Voice Transformation Creativity Narrative Composition Use of colour / tonality Depth of Field Use of Light Basics Focus Technical Exposure Courtesy of Bob Ryan

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5 Depth of field - Only the subject in focus

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7 Standard camera exposure

8 2 stops under Standard camera exposure

9 1.25 stops over Standard camera exposure

10 Standard camera exposure

11 Standard camera exposure Adjusted for shadows and highlights

12 Exposure An ideally exposed photo would capture all the detail in both highlights (bright areas) and shadows (dark areas) The human eye, in conjunction with the brain, is very good at seeing detail in both very bright areas and very dark areas This is called dynamic range Film has a higher dynamic range than digital Both have a lower dynamic range than human sight An exposure for an image has to compromise between the bright and dark areas in the image The compromise will be based on the relative percentage of bright and dark areas the area over which the metering is done

13 Exposure Exposure is controlled by a balance between Shutter speed Aperture Sensor sensitivity (ISO rating) This is equivalent to film speed The higher the rating, the more sensitive the film, but the bigger the grain (noise) One is normally considered fixed and the other two varied White balance is also involved This affects the tint or cast of the image With digital the number of options to consider has increased Hence Auto mode a mini AI (even more so with the latest Smart Phones)

14 Exposure Exposure is concerned with the amount of light that reaches the sensor (film) A sensor is composed of a number of pixels Each pixel gathers light independently of its neighbours Consider a pixel as a container that we are going to fill with light A pixel only has a certain capacity, So if it s overfilled the extra light is lost This is overexposure If it s underfilled there is a very dim image Underexposure

15 Exposure: Aperture Each doubling or halving of a control is called a Stop f Number Squared f/1 1 1 f/ /2 f/2 4 1/4 f/ /8 f/4 16 1/16 f/ /32 f/8 64 1/64 f/ /128 f/ /256 f/ /512

16 f Number N = f or D = f D N f is the focal length e.g. 200mm D is the diameter of the aperture N is the f number For a focal length of 200mm and an aperture of f/4, the diameter of the aperture = = 50mm For a focal length of 200mm and an aperture of f/16, aperture = = 12.5mm

17 Exposure Light has a dual nature Wave frequency Particle photons Analogy is considering light as particles photons Dull day is normal rain Bright day is heavy rain On bright day heavy rain need a small aperture or a fast shutter speed to avoid over filling the container Sometimes the rain is too light and you need another variable the ISO rating

18 Exposure: Aperture vs Shutter Speed To fill up to a given level, a wider aperture must be open for a shorter time Small aperture Longer shutter speed Large aperture Shorter shutter speed

19 Exposure: Aperture vs Shutter Speed Aperture and Shutter Speed move in opposite directions to maintain an optimum exposure Aperture Shutter Speed f/4 1/800 f/5.6 1/400 f/8 1/200 f/16 1/50 f/22 1/25 What is the other major consequence of a longer shutter speed?

20 Exposure: Dynamic range Each pixel can be considered as a container No water is black Full is white There is an optimum range that represents a useable range of well exposed darks and brights

21 ISO Rating Also goes in a binary sequence, 50, 100, 200, 400, 800, 1600, 3200, 6400, 12800, If shutter speed is held constant and aperture changed, then ISO must change to maintain an optimum exposure Shutter Speed Aperture ISO Rating 1/200 f/ /200 f/ /200 f/ /200 f/ /200 f/ What is the consequence of using a higher ISO?

22 Noise

23 Noise

24 Noise Short exposure Long exposure

25 Noise Dark area Light area

26 Noise

27 Noise Green Blue Red Colour suggestion is, Red 50%, Blue 30%, Green 20% but we only have 10 out of 160 pixels sampled 6% 2 3 5

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29 Exposure: ISO rating The larger a pixel, the more water it can contain No two pixels capturing the same colour and amount of light will be filled to the same level The dark blue represents this randomness Increasing the ISO means less water is required for a given exposure The randomness is a greater percentage of the volume and therefore clarity is poorer Standard ISO Higher ISO

30 Exposure: ISO rating The larger a pixel, the more water it can contain Increasing the ISO means less water is required for a given exposure But to see a picture the volume needs to be multiplied The randomness is a greater percentage of the multiplied volume and therefore clarity is poorer Standard ISO Higher ISO

31 Noise High ISO Multiplied Volume

32 ISO 1/1000 f/5.6 ISO mm Stops Down Amount of Light / / / / / / / /256

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34 Noise

35 Metering Measures the amount of light and decides on aperture and shutter speed to achieve optimum exposure Normaly three different ways of measuring exposure The whole frame Centre weighted Spot

36 Standard camera exposure

37 Aperture Controls Exposure Depth of field Depth of field varies by Size of sensor Focal length Decreases with longer focal length Where the focus point is

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39 Shutter Speed Controls Exposure Ability to freeze motion Affects Blurring due to camera movement Effect of camera movement increases as focal length increases Basic rule is 1/(focal length) as minimum shutter speed Most cameras now have image stabilisation Enables shutter speed to be 3 to 5 stops lower e.g. at 200mm telephoto standard would be 1/200 with image stabilisation of 3 stops could be 1/25

40 White Balance Work on Auto for most images White balance for RAW does not matter - can be adjusted later Typical pre-sets

41 RAW image with incorrect White balance

42 RAW image with corrected White balance

43 Camera Control Mode Camera sets User sets Nikon (and most cameras) Canon Aperture Shutter speed Aperture A AV Shutter Speed Aperture Shutter Speed S TV Manual - Aperture and Shutter Speed Program Aperture and Shutter Speed Relationship between shutter speed and aperture Auto Everything Nothing Auto Auto M P M P

44 Camera Control Scene Modes Scene Mode Camera sets Aperture Shutter Speed Nikon (and most cameras) Landscape Smaller Slower Or similar Sport Larger Faster Or similar Portrait Larger Slower Or similar Night Larger Slower Or similar Canon Camera will try to use lowest ISO, but has option to increase e.g. in Sports mode

45 Exposure Compensation Two options Do it manually Use camera control to move up or down a number of stops

46 Focus Auto-focus modes Whole frame Centre Spot Specified spot Face

47 Raw vs JPEG Light to dark RAW 12 bits 4096 shades (x16) 14 bits 16,384 shades (x64) JPEG 8 bits 256 shades White balance Not set Set Contrast Not set Set Colour Saturation Not set Set Sharpness Not set Set Noise reduction Not set Set Quality Intact Lossy compression format

48 12MP 9.6MB 581, MP 458KB 292, (4x) 256 (3x) 16 (6x)

49 12MP 9.6MB 581, MP 458KB 292,047

50 256 (3x)

51 64 (4x)

52 16 (6x)

53 100% 1MB

54 70% 123KB

55 40% 72KB

56 10% 36KB

57 5% 34KB

58 Standard camera exposure JPEG image

59 Standard camera exposure JPEG image; 2 stops under

60 Standard camera exposure RAW image; 2 stops under

61 Standard camera exposure - JPEG Adjusted for shadows and highlights

62 Standard camera exposure - RAW Adjusted for shadows and highlights

63 Camera Image Display Small display always flatters an image Image displayed is a JPEG If you shoot in RAW, camera will use its opinion of settings to make the image

64 - 2 stops RAW JPEG Shadows & Highlights

65 -2stops JPEG RAW Shadows & Highlights

66 Not hearing is not as good as hearing, hearing is not as good as seeing, seeing is not as good as knowing, knowing is not as good as acting; true learning continues until it is put into action. Xunzi (Xun Kuang c. 310 c. 235 BC)

67 Homework Find a scene with even lighting Example settings Set metering to full frame 1. Take a photo on auto or P mode Note the shutter speed and aperture 2. In Manual mode, set the shutter speed and aperture to settings from auto mode Take photo 3. Set the shutter speed to 2x, adjust aperture Take photo 4. Set the shutter speed to ½x, adjust aperture Take photo 5. Take photo one stop under-exposed 6. Take photo one stop over-exposed Set metering to centre-weighted Repeat photos as for full frame metering Find a scene with very bright and very dark lighting, e.g. person taken against a window Repeat all the steps for the first scene Step Mode Aperture Shutter 1 P (or Auto) f/8 1/200 2 Manual f/8 1/200 3 Manual f/5.6 1/400 4 Manual f/11 1/100 5 Manual f/8 1/400 6 Manual f/8 1/100

68 Notes to Homework If the camera does not have one of the mode dials as shown in slide 44, it should be available in the menu somewhere You may have to experiment to find out how to set the shutter speed and aperture Use the f-stop table in slide 5 to move the aperture up and down from the settings your camera gives you in Auto. The example settings given for the homework may not bear any relation to what your camera uses for your chosen scene. You may have to display the image you take on P (or Auto) and hunt around for an option that displays the settings used for your image. If your camera uses an SD card, then you can just bring the SD card along to the next session. If not, transfer the images to a USB memory stick and bring that. The next session will look at using flash and discuss what you have done and learnt in the homework.

69 Extended Homework 1 What alternatives does your camera have for overexposing or underexposing? Take all the images in both RAW and JPEG Take all the images at your highest and lowest JPEG quality Later we can look at the differences in processing

70 Extended Homework 2 Place 6 objects in a row about 6 inches apart Focus on the 1 st object Take a photo of the objects at three different apertures note your distance from 1 st object Focus on the 3 rd object Take a photo of the objects at three different apertures

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