Camera PrinciplesScene Image Resulting image is mirrored and inverted Small aperture results in very long exposures Light Rays Pinhole Camera
Camera PrinciplesScene Image Increasing the pinhole size provides more light to shorten exposure times but introduces distortion of light rays resulting in poor Light Rays Pinhole image quality Camera
Exposure Control Aperture value controls amount of light Shutter speed controls duration exposure of time Combination of aperture and shutter speed gives correct exposure - for a particular light sensitivity Combination defined as an exposure value (EV) Standard light sensitivity is 100 ISO (ASA) Higher light sensitivity provide faster exposure times Lower light sensitivity provide slower exposure times Fast film has a more grainy structure than slow film
Exposure Control: Aperture Aperture controls amount of light via lens iris Iris adjusted by changing aperture value on lens Large f number = smaller iris size = less light Small f number = larger iris size = more light
Exposure Control: Shutter Shutter controls time light exposed to medium Typical ranges 1 second - 1/2000th sec Shorter (faster) shutter speeds = less time Longer (slower) shutter speeds = more time Shutter positioned at the focal plane or between the lens (medium format) Focal plane shutters can be horizontal run or vertical run
Exposure Balancef stop shutter speed Sensitivity of filmf 5.6 1 / 500th 100 ISO
Exposure Balancef8 1 / 250thf 11 100 ISO 1 / 250thf8 200 ISO 1 / 500th 200 ISO
Exposure Balance: Three-Way Exposure balanced between medium sensitivity aperture value and shutter speed Double or half the sensitivity = one ‘stop’ Double or half the shutter speed = one stop Aperture values change by a factor of 1.4 = one stop
Exposure Modes Manual - you set aperture and shutter speed based on light reading Aperture Priority - you set aperture and camera calculates and sets the shutter speed based on light reading Shutter Priority - you set the shutter speed and camera calculates and selects aperture based on light reading Fully Programmed - Camera selects both aperture and shutter speed based on light reading
Lenses Lenses interchangeable on SLR cameras Lens bayonet - mounts to camera body Each manufacture’s lens mount is unique Lenses available from independent lens manufactures and for several different lens mount Lenses provided by independent manufactures are generally less expensive than camera’s own brand May not be as good optically or have same build quality as cameras own brand lenses
Standard Lenses (35mm)50mm f1.8 50mm f1.4 50mm f1.2
Wide Angle Lenses28mm F 2.8 20mm F 3.5 15mm F 3.5
Angle of View for 35mm 50mm provides natural perspectiveShorter focal length lenses have angle of view which gives for the 35mm formatsteeper perspectiveLonger focal length lenses have narrow angle of view whichgives flatter perspective
Advanced features Autofocus Image stabilisation Intelligent recognition of faces and scenes
Autofocus (3) The microprocessor in the camera looks at the strip of pixels and looks at the difference in intensity among the adjacent pixels. If the scene is out of focus, adjacent pixels have very similar intensities. The microprocessor moves the lens, looks at the CCDs pixels again and sees if the difference in intensity between adjacent pixels improved or got worse. The microprocessor then searches for the point where there is maximum intensity difference between adjacent pixels -- thats the point of best focus. Look at the difference in the pixels in the two red boxes above: In the upper box, the difference in intensity between adjacent pixels is very slight, while in the bottom box it is much greater. That is what the microprocessor is looking for as it drives the lens back and forth.
Autofocus (4) Passive autofocus must have light and image contrast in order to do its job. The image needs to have some detail in it that provides contrast. If you try to take a picture of a blank wall or a large object of uniform color, the camera cannot compare adjacent pixels so it cannot focus. There is no distance-to-subject limitation with passive autofocus like there is with the infrared beam of an active autofocus system. Passive autofocus also works fine through a window, since the system "sees" the subject through the window just like you do. (Courtesy How Stuff Works)
Image stabilisation Canon’s newly developed Hybrid IS technology optimally compensates for angular camera shake (rotational) and shift camera shake (linear). Sudden changes in camera angle can cause significant blur in images taken during standard shooting, whereas blur caused by shift-based shaking, when a camera moves parallel to the subject, is more pronounced in macro and other close-up photography.
IS: How is it done? The new Hybrid IS technology incorporates an angular velocity sensor that detects the extent of angular camera shake which is found in all previous optical Image Stabilizer mechanisms, as well as a new acceleration sensor that determines the amount of shift-based camera shake. Hybrid IS also employs a newly developed algorithm that combines the output of the two sensors and moves the lens elements to compensate for both types of movement. Hybrid IS dramatically enhances the effects of Image Stabilizer especially during macro shooting, which is difficult for conventional image stabilisation technologies.