Shutter Speed

1. Shutter Speed • Controls the exposure time. It must be reasonably fast. • 1/15 sec, 1/30, 1/60, 1/120, 1/250, 1/500, … • The slower shutter speeds need good camera support, like a tripod. You can shoot close-up portraits of people who can hold still at 1/4 sec, but it’s risky. Better to use 1/8 sec and faster if your subject doesn't remain still..

2. Low light levels require a slow shutter speed for proper exposure. Slow shutter speed reveals motion, shown particularly by the dancer's blurred hands.

3. A medium shutter speed is all that is needed when the subject is not moving very fast. A point and shoot camera will automatically select a fast shutter speed in bright sunlight

4. A fast shutter speed was used to freeze this bike rider in mid-air. Pin-point sharp, stop-action photography is made possible by very fast shutter speeds, but focusing must be accurate

5. Must be able to expose all parts of the film equally throughout the exposure • Between-the-lens shutter: near the lens • Focal-plan-shutter: expose the film strip by strip, can get deformed images of the rapidly moving objects. Two types of shutter

6. Stops or Aperture • An opaque barrier with a hole — a device to limit the width of a light beam. • By varying the diameter of the aperture, you control the amount of light passing through the lens into the camera to expose the film. • A large aperture (or wide lens opening) lets in more light than a small one, and can deliver the same brightness from a dimly-lit subject as a small aperture will deliver from a brilliantly-lit subject.

7. f-number • f-number = focal length / diameter of stop’s hole example: f = 50 mm, d = 12.5 mm Then f/d = 4, which is written as f/4. • For a fixed focal length, the f-number tells you directly the size of the stop. • For the same f-number, the image has the same amount of intensity.

8. It seems contradictory but is important for you to remember that a larger ƒ-stop number designates a smaller lens opening, and vice-versa. For example, an aperture of ƒ/22 is a very small lens opening, whereas an aperture of ƒ/1.4 is a relatively huge opening, and will let a great deal more light pass through the lens. f-number

9. The bottom row of numbers (16, 11, 8, etc.) on this lens shows the aperture settings of the lens, which is currently set at ƒ-5.6. The numbers are inscribed on an adjustable "aperture control ring."

10. An aperture of f16 is a small opening! An aperture of f/1.4 is a wide opening!

11. F-number and intensity of light • If you increase the f-number by a factor, you cut down the light by the square of that factor. • The area is proportional to diameter squared. • Double the f-number, get ¼ of light! • Why f-number involves the focal length? • For a fixed stop, larger the focal length, less the intensity of the light.

12. 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 betweenf2 and f22? f2 lets in more light, f22 lets less, the difference is (22/2)2 = 121 F-number sequence

13. Exposure • For a given lighting condition, the exposure is theproduct of the light-intensity times the exposure time, where the light-intensity is related to the f-number. • Light intensitycan be measured using exposure meter. • If film receives the correct amount of light, the resulting picture reproduces the subject in all of its proper tones and colors. Such a picture is said to have been "properly exposed."

14. One can get the same exposure by increase the f-number and the exposure time by the same factors. In a bright sunny day… f/11 and 1/60 sec f/8 and 1/120 sec Gives the same exposure If an object is moving, you want to have shorter exposure time. Choosing Exposure

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

16. Film • Chemicals which react when exposed to light • Silver compound of chlorine, bromine or iodine (silver halides), discovered in 1830s • Light strikes the silver halide (crystal), breaking chemical bond and yielding metallic silver • Nuclei • Latent image: distribution of the nuclei.

17. Positive and negative images • If the film is developed so that the final image is white where the original subject is bright, we have a positive image. • Two methods of development • Physical development (Dagurre and Talbot, used in photocopiers) • Chemical development (what we used mostly) • Fixing the image • Using hypo to wash away the unexposed halides.

18. H & D Curve • How to record the color between white and black (gray)? • Use crystals of different sizes. Large crystals are easily exposed by weak light and small crystals are only active at very strong light. • The reaction of film, or the density of the nuclei is a function of the exposure. The relation can be shown by a curve, called H & D curve.

20. Speed, Contrast and Latitude • Speed.The initial rise (toe) of the H&D curve represents measure the speed of the film. Lower the exposure at the toe, faster the film. • Contrast: the slope of the curve determines the sensitivity of the film to the different exposure. Larger the slope, bigger the contrast. • Latitude: How long is the steep part of the curve? It represents the range of exposure.