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Photography! Exposure Basics.

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by

Chia Wei Ong

on 10 April 2012

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Transcript of Photography! Exposure Basics.

Aperture Shutter Speed ISO (sensitivity) Exposure
triangle expressed in f stops
smaller f stops = larger aperture
e.g. f/1.4 is larger than f/2.8
f/8.0 is smaller than f/5.6 small aperture (f8 or f11): wide depth of field
large aperture (f1.4 or f2): narrow depth of field f2 f4 f8 f16 usually expressed in a fraction of a second
e.g. 1/50s, 1/200s
so 1/400s is faster than 1/50s
1/20s is slower than 1/70s slow shutter speeds cause motion blur
due to:
1. camera shake
2. subject movement 1/13s 1/50s higher ISO implies higher sensitivity
ISO100, ISO200, ISO400 and so on high iso introduces
grain or noise ISO100 ISO800 ISO6400 So what does aperture, shutter speed and sensitivity have to do with exposure?
Aperture determines how much light goes through the lens to the sensor

A larger aperture - f2.8 allows more light to reach the sensor than a small aperture - f8 or f11 Shutter speed determines how long the sensor is exposed to light

A faster shutter speed - 1/200s allows less light to reach the sensor than a slower shutter speed - 1/40s Sensitivity is how much the sensor amplifies the light as a signal to create the final image

At ISO400, the camera sensor is more sensitive to light than at ISO200 aperture x shutter speed x sensitivity = exposure now let's apply this in terms of camera usage Most dSLR and advanced compact cameras have PASM modes:
- Program
- Aperture Priority
- Shutter Priority
- Manual Metered Modes In P mode, the camera sets the Aperture and Shutter Speed to expose a scene In A mode, user sets the Aperture, camera sets the Shutter Speed to expose a scene In S mode, user sets the Shutter Speed, camera sets the Aperture to expose a scene In these modes, the camera meters the scene and tries to set an exposure appropriate to the scene.
It does so by changing the variables it can change in one of the P A S modes. In M mode, user sets the Shutter Speed and Aperture to expose a scene sometimes the camera isn't so smart
underexpose
overexpose
backlit
spotlit let's have an example User is in P mode
ISO is set at 400
The camera looks at the scene, tries to balance the Aperture and Shutter Speed to a reasonable setting - f4.0 and 1/80s
If the user sets the ISO to 200, it will automatically compensate the variables to attain the same exposure - f3.5 and 1/50s User is in A mode
ISO is set at 400
The user has set the Aperture to f2.8
The camera looks at the scene and sets the shutter speed at 1/160s.
If the user changes the aperture to f4.0, the camera will automatically compensate the shutter speed to 1/80s to attain the same exposure it may sound confusing... When a camera looks at a scene
it already has in it's 'mind' what level of exposure it should have so that the picture will not be too bright or dark. Since exposure is determined by the 3 variables:
Aperture
Shutter Speed
Sensitivity underexposed
too dark nicely exposed
just right overexposed
too bright If one of the variables is changed by the user, the camera will 'help' the user by changing the other variables, so that the picture still has the same exposure, and is neither too bright nor dark What does that mean for the user? Remember the 'side' effects of Aperture, Shutter Speed and Sensitivity? You can change any one of the variables (to creatively control your picture) and the camera will try in it's best way to maintain the same level of exposure for your pictures! You can increase the depth of field by reducing the aperture from f2.8 to f5.6, and the camera will help you change the shutter speed without you having to worry too much about it (unless it is too slow, then you have to increase the ISO to balance it out) In summary, remember this P A S M
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