Lec. 13: Ch. 4 The Camera and Photography. Camera parts

Transcription

1 Lec. 13: Ch. 4 The Camera and Photography Camera parts We are here 1. Lens, focal length 2. Shutter (on the lens) 3. Diaphragm (on the lens) 4. Focusing screen or LCD 5. Film (or CCD chip) Tuesday, October 5, 2010 We covered these 26 slides. 1 Exam 1 Histogram Median score = 50. A >65 about B > 50, Failing <38 about. Frequency C B A F 100 More

2 Film how it works 1. Plastic film is coated with emulsion containing a silver compound (silver bromide). The coated side faces the lens. 2. Light breaks chemical bonds with silver. This is the latent image. 3. Chemical developer releases silver into black grains. This is the negative image. 4. A lens system projects the negative image onto a piece of coated paper, which is developed into a positive image. 35 mm film comes in a light-tight cartridge 3 Positive and negative. The print The film (negative) 4

3 Latent image Developed image μ = micrometer 5 Film speed and ASA number Faster film (ASA400) needs less light. Trade-off: Faster film is grainier, (bigger grains) meaning less detail in the image. Film speed has a number: ASA 25 is slow with fine grain. Use outside in sun. For example, in sunlight, f/8 and 1/25 sec. will be ok. ASA 100 is medium speed, good for inside shots. In sunlight, f/8 and 1/100 sec. ASA 400 is good for low lighting. In sunlight, f/8 and 1/400 sec. 6

4 Photography (cont d) Polarizing and haze filters Tripod 35 mm slides 7 Polarizer selects one polarization (rejects the other) Sunlight is randomly polarized Polarization is perpendicular to the plane containing the incident and scattered rays (vertical for low sun) Walden pond Polarization parallel to the water surface (horizontal) 8

5 UV/Haze filter Scattered sunlight from tiny particles (including atoms) contains more blue and UV. Hint: That is why the sky is blue, ocean is blue. Haze is sunlight scattered from tiny particles. UV filter does not pass the scattered UV so the scene is less hazy. Haze Haze Haze Haze Yellow fog lights on cars don t contain blue that would scatter from the fog. 9 Tripod Holds the camera steady for long exposures Astronomy, indoors (museums, weddings) Low light, any exposure 1/5 sec or longer Telephoto lenses, 1/100 sec or longer 10

6 35 mm film photography We look at 35 mm color slides that show Wide angle and telephoto lens Depth of field Shutter speed Harsh and soft lighting Rainbows, fog, crepuscular rays, etc. Perspective Moon, comet Caves Demo: slide show, next slide is black for projection of slides 11

7 Lec. 13: Ch. 4 The Camera and Photography We are here Photography as art Camera parts Photography as science Scientific photography and imaging Photomicrography Stop action Time lapse video photography Astrophotography ground based space based Not-light photography 14

8 Photomicrography Insect leg 15 Harold Edgerton flash photography 1940s & 50s A fast flash of light, 1/10,000 sec. for example, stops motion Milk drop onto red surface Water faucet 16

9 More Edgerton photos Duration of flash of light is probably a few microseconds. 17 Time lapse Take photos at 1 sec intervals (for example) Show at 30 frames per second (for example) Milky Way rising Shot at 1 minute per frame, shown at 30 frames per sec., 1800 times normal speed Mentos and Diet Coke (1200 fps) 1/40 of normal speed San Francisco time lapse 18

10 Astrophotography Hubble Telescope The large mirror intercepts lots of light and concentrates it onto the film or CCD detector. Long exposures, hours, are used. 19 Hubble astrophotographs 20

11 Not-light photography X-rays shadowgraphy Computer aided tomography (CAT) Ultrasound, sonar Radio astronomy Magnetic resonance imaging (MRI) 21 Radio astronomy maps radio brightness Galaxy M87 squirts a jet of material. The detail shows the origin of the jet. Probably, the source is powered by a black hole. Images are computer-constructed using many antennas. 22

12 Ultrasonography f = 2 18 MHz implies wavelength of about 0.1 mm 23 X-ray shadowgraph (2-d) There is no focusing lens. The x-rays go from a point-like source to the film. What is recorded is a negative of a shadow. 24

13 X-ray tomography (3-d) A computer produces a 3-d image from many x-ray shadows from different directions. Shown above is someone s head. 25 Magnetic resonance imaging (MRI) The science: a magnetic field and radio waves detect spinning nuclei in atoms. The location of the signals can be pinpointed and made into an image by computers. Advantage: better discrimination between types of tissue. Disadvantage: expensive 26