Shutter Speed Controls the exposure time. It must be reasonably fast. 1/15 sec, 1/30, 1/60, 1/120,...
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Transcript of Shutter Speed Controls the exposure time. It must be reasonably fast. 1/15 sec, 1/30, 1/60, 1/120,...
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..
Slow shutter speed reveals motion, shown particularly by the dancer's blurred hands.
Low light levels require a slow shutter speed for proper exposure.
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
Pin-point sharp, stop-action photography is made possible by very fast shutter speeds, but focusing must be accurate
A fast shutter speed was used to freeze this bike rider in mid-air.
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
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.
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.
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
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."
An aperture of f/1.4 is a wide opening!
An aperture of f16 is a small opening!
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.
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
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. Light intensity can 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."
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 secGives the same exposure If an object is moving, you want to have
shorter exposure time.
Choosing Exposure
High shutter speed froze this explosion's debris in mid-air
A small aperture provided this image with plenty of depth of field
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.
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.
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.
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.