F-number sequence. a change of f-number to the next in the sequence corresponds to a factor of 2 change in light intensity,

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2 F-number sequence a change of f-number to the next in the sequence corresponds to a factor of 2 change in light intensity, 0.7, 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, Example: What is the difference in light intensity between f/2 and f/22? f/2 lets in more light, f/22 lets less, the difference is (22/2) 2 = 121 Each f-stop differs by ~ Sqrt[2] = 1.4 2

3 Why does the f/# work? f/#= f/d - why divide by focal length? Long focal length short focal length The area of the image goes like f 2 amount of light goes like d 2 3

4 Exposure For a given lighting condition, the exposure is the product of the light-intensity times the exposure time, where the light-intensity is related to the f-number. Shutter speeds and f-numbers use power of 2 sequences so: f/11 and 1/60 sec f/8 and 1/120 sec f/5.6 and 1/250 sec all give the same exposure 4

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6 Why does the moon look properly exposed? 1. It s a bright sunny day on the moon 2. It s faked with Photoshop 3. It was really dark when the picture was shot 6

7 What to point the light meter at? The exposure meter/control is designed to adjust for ambient light of the scene Rule of thumb For Shutter speed = 1/ISO (ASA) Bright/sun Cloudy/bright Cloudy dark/cloudy f/16 f/11 f/8 f/5.6 Meter is calibrated for 18% grey card Also - green grass, blue sky Palm of hand is about 35% reflective so open up a stop 7

8 Exposure : f/number vs. shutter speed Amount of light f/16 1/60 sec f/8 1/250 sec time Large depth of field Good for stop-action Both give equal exposures 8

9 High shutter speed froze this explosion's debris in mid-air A small aperture provided this image with plenty of depth of field 9

10 Flash Photography use in low light levels do not have to worry about camera or subject motion film color changes at very low light/long exposure used as fill, to light shadowed areas Flash duration ~ 1 ms typical camera sets shutter at 1/60 sec for flash ~1 ms 16 ms 10

11 Digital camera lenses Why don t digital cameras use std. 35mm lenses? 35mm film - 24X36mm 6 Mpixel sensor - 16X24mm Smaller sensor - use shorter focal length lens (1.5x) 11

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14 Flash Photography use in low light levels do not have to worry about camera or subject motion film color changes at very low light/long exposure used as fill, to light shadowed areas Flash duration ~ 1 ms typical camera sets shutter at 1/60 sec for flash ~1 ms 16 ms 14

15 Digital Photography 15

16 Pixels Digital cameras break image up into pixels (picture (pix) elements (els)) 16

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23 Image sensors replace film Digital vs. Analog Film is a analog (continuous) medium exposure Amount of light Image sensors digitize the amount of light Image is a series of numbers 23

24 Digitization Binary arithmetic Bits - 0 or 1 8-bit different levels = = = 119 Most cameras have 12 bits (4096) levels Logarithmically scaled 24

25 CCDs Image sensors - Charge coupled device each pixel is a miniature photodiode - converts light into electrons stores electrons readout after exposure electronics (ADC-analog-digital converter) counts electrons string of numbers representing light intensity at each pixel 25

26 How many Pixels? counted as Megapixels (10 6 pixels) cheap (< $100) cameras 2-3 Mpixels good ($ ) Mpixels professional ($500-8,000) Mpixels How much do I need? 35 mm film (24X36mm) is equivalent to ~15-25 Mpixels most photoprinters give at best 200 dpi 4 X6 photo needs 800X1200 pixels ~ 1 Mpixel! why buy 10 Mpixel camera?? 26

27 Compression High Mpixel means big image files Each pixel has information about 3 colors Cameras offer different levels (quality) of compression (to make smaller files) Lose some information Depends on image (e.g. blue sky is easy) If you buy many pixels, but use always use low resolution, you have wasted your money! 27

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32 Resolution Low resolution 640X480 File size: 240 kb High resolution 2048X1536 File size:1.8 MB 32

33 Low resolution 640X480 High resolution 2048X

34 Color photodiodes are not color sensitive add color filters on each pixel (RGB) Bayer filter note twice as many green as red and blue 34

35 Image processing Use information from neighbors to determine color de-mosaicing RAW file format - straight from camera 35

36 Optical vs. digital zoom Optical zoom Move lens/lenses Digital zoom Just use smaller portion of sensor No different than cropping high resolution picture! Lose resolution - use fewer pixels Only benefit is that it saves space on camera. 36

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40 CMOS - the future CMOS - Complementary metal oxide semiconductor same electronics as most semiconductors used to be less sensitive than CCD faster readout lower power consumption - battery life! 13.3 Mpixel CMOS sensor 35mm format! - use std. 35mm lenses 40

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42 Saturation 42

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44 Question: Using my digital SLR with lenses of focal length, 20mm, 55mm and 200mm, what is the field of view for a photo taken 5 meters away? We need to know digital sensor size (analogous to film frame size) For the digital SLR, this is 16mm by 24mm 44

45 Field of View of 10mm Lens at distance of 5 meters M = IH/OH = F/OD OH/IH = OD/F OH/2.2cm = 500cm/1cm OH OD ID IH OH = cm M = IH/OH F/OD Image OH = 1100cm = 11m Object Lens 45

46 Field of View of 20mm Lens at distance of 5 meters M = IH/OH = F/OD OH/IH = OD/F OH/2.4cm = 500cm/2cm OH OD ID IH OH = cm M = IH/OH F/OD Image OH = 550cm = 6m Object Lens 46

47 Field of View of 55mm Lens at distance of 5 meters M = IH/OH = F/OD OH/IH = OD/F OH/2.4cm = 500cm/5.5cm OH OD ID IH OH = cm M = IH/OH F/OD Image OH = 200cm = 2.2m Object Lens 47

48 Field of View of 200mm Lens at distance of 5 meters M = IH/OH = F/OD OH/IH = OD/F OH/2.4cm = 500cm/20cm OH OD ID IH OH = cm M = IH/OH F/OD Image OH = 55cm =.6m Object Lens 48

49 Summary of results Field of view at a distance of 5 meters Focal length 20mm 55mm 200mm Field of view 6 meters 2.2 meters 0.6 meters 49

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53 Foreground emphasis 1 m Wide angle picture, use 20mm lens.. Relative size of background = d 1 /d 2 = 1/5 4 m Photographer moves close to subject to take picture. Background person is five times as far away as foreground person. Magnification is one fifth for background person 53

54 Theory: telephoto compression 2 m 20m 2 m telephoto picture, use 200mm lens. As before film is 22mm across, assume full frame picture. Relative size of background = d 1 /d 2 = 20/22 Photographer moves far away from the subject to take picture. Background person is only slightly farther away than foreground person (22m vs 20m). Magnification is nearly identical for background person 54

55 Theory: telephoto compression 2 m 2 m 2 m Wide angle picture, use 20mm lens. As before film is 22mm across, assume full frame picture. M = IH/OH = ID/OD 2.2cm/200cm = 2cm/OD 200cm/2.20cm = OD/2cm OD 200cm = 2m Photographer moves close to subject to take picture. Background person is twice as far away as forground person. Magnification is half for background person 55

56 Theory: telephoto compression 2 m 20m 2 m telephoto picture, use 200mm lens. As before film is 22mm across, assume full frame picture. M = IH/OH = ID/OD 2.2cm/200cm = 20cm/OD 200cm/2.20cm = OD/20cm OD 2000cm = 20m Photographer moves far away from the subject to take picture. Background person is only slightly farther away than foreground person (22m vs 20m). Magnification is nearly identical for background person 56

57 Telephoto compression (photos from late time) Wide angle lens photo Telephoto lens photo Compression happened because I was farther away. 57

58 Wide Angle Telephoto 58

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61 What does anamorphic mean? One cylindrical lens focuses rays horizontally another cylindrical lens focuses rays vertically Vertical magnification is smaller than horizontal magnification The image gets squished. 61

62 Anamorphic DVD Original scene Squish into 4:3 frame Fancy video monitor un-squishes 62