Book Topics and Notes:
Chapter 3: How Digital Cameras Work
From a practical point of view, focal length can be thought of as the amount of a lens's magnification.
Also effects compression of the scene, perspective and Depth of Field
Measures the amount of light the lens ttransmits at maximum aperture
A fast lens is more desirable and is usually more expensive
can also help the lens focus
Effects image quality
Recognizing Lens Problems
Straight lines near the edges of an image bend inward
Bulging of the scene, straight lines near the edge of the image bend outward
May create colored halos at bright edges of an image
The Viewfinder and LCD
Advantages and Disadvantages
Can check lighting, composition, holding away from the eye
Uses a lot of power, hard to see on a bright day
LCD vs Viewfinder
Many digital cameras don't use a mechanical shutter
Pushing the button
A more inexpensive camera will be slower to respond
Shutter lag time
You might be able to depress the shutter halfway to decrease it
More expensive cameras often have less
The Imaging Sensor
Types of Sensors
CCD vs CMOS
CCD still more common, but CMOS getting better
CCD uses more power and costs more to produce
Fuji Super CCD Sensor
Octagonal pixel shape
Foveon X3 Sensor
Sees all colors
often scan 3 times, 1 for each color
only good for still objects
How Sensors Work
When too many photons hit a particular pixel and the electrical charge becomes more than it can handle, the charge starts to overflow into surronding pixels.
Analogue to digital conversion
The process by which analogue signals are converted into discrete digital values.
Amplification of the signal, such as shooting at a high ISO rating, or heat can increase noise.
When to change ISO
Only if you have to
Physical size of the sensor
Impact on Focal length
When an imaging sensor is smaller than the film it replaces, it's cropping the image circle projected by the lens.
Wide angle lenses aren't so wide angle.
Impact on Image quality
Lenses tend to be sharpest at the center, so the cropping of the image by the image sensor may produce a sharper image.
Physical size of the pixels
Impact on ISO
Larger pixels have more surface area to absorb light, giving them a higher sensitivity, or higher effective ISO.
Impact on Image Quality
Larger pixels produce an image that is coarser because they are not able to capture as much dertail; smaller pixels resolve finer detail.
Because smaller pixels are less sensitive, the signal they produce will generally need to be amplified, resulting in more noise.
Higher bit depths are better for providing extra info if needed for substantial tonal and color image editing.
Usually only available with RAW Capture mode.
Imaging sensors are color blind; they only measure brightness.
Is the ability to capture an image with full tonal detail from bright highlights to dark shadows.
If your camera doesn’t provide an adequate dynamic range to hold detail in all tonal values in your image, it’s best to underexpose the scene by 1/2 to 1 stop. Areas that are too bright and contain no information can’t be fixed. It’s better to lighten a dark image than darken a light one.
Also recommended to not use in camera options to increase image contrast or saturation.
Storing the image
compact flash, microdrive, smartmedia, memry stick, xD-Picture Card
Lack of control and red eye can be problems
Better control of exposure and effect of the lighting
Many cameras use the diaphragm to shield the image sensor, and have no shutter.
No shutter means no shutter noise.
The lens element refracts light from the real world onto the image sensor.
The number of pixels captured by the image sensor is commonly known as the resolution.
Megapixel=Millions of pixels in an image.
Higher resolution images have more detail.
More compression effects image quality.
CCD vs CMOS
Digital camera file formats
JPEG: Joint photographic experts group.
JPEG's use compression and are lossy(doesn't change pixels).
TIFF: Tagged Image File Format. Has little compression and is lossless. Can be used for printing.
Chapter 4: The Mechanics of Digital Imagery
A word processor uses 8 bits to express a character for type. A grayscale image uses this much memory to store the data for 1 pixel.
A black and white image contains 1 bit per pixel(each pixel is black or white), a grayscale image contains 8 bits per pixel for 256 shades of gray, and a full color image contains 24 bits per pixel, showing 16.8 million colors.
Downsampling means to reduce the number of pixels by interpolating the colors of the existing pixels.
Images for the web are usually saved at 72 dpi, but browers will probably ignore the actual resolution and show the image at a 1 to 1 zoom ratio. You see 1 image pixel for every screen pixel.
For print, the resolution of the image should be about 2 times the screen frequency.
|Printer||Ideal Resolution(2 x screen frequency)||Good Enough(1.5 x screen frequency)||Absolute Maximum(2.5 x screen frequency)|
|300-ppi Laser printer||120 ppi||90 ppi||150 ppi|
|600-ppi Laser printer||180||135||225|
|Coated Magazine Stock||267||200||330|
|Super-fine Magazine Stock||350||260||440|
GIF (graphic Interchange Format)
Other file formats
EPS(encapsulated postscript) used for printing.
PDF(portable document format) good for exchanging documents on disk or over the web. Requires viewer to see.
PNG(Portable Network Graphic) Web file format which hasn't caught on.
Chapter 5: Bells and Whistles: The Digital Camera Interface
Rangefinder verses SLR(Single-Lens-Reflex). Parallax error with rangefinders.
Serial: 150 to 230 kilobits per second
USB(Universal Serial Bus): 12 megabits(1.1 Megabytes) per second. Hot swappable.
USB 2:480 megabits per second? Not widely supported yet.
Firewire(IEEE1394) 400 megabits per second.
Cardreaders and adapters.
Chapter 9: Essentials of Photography
Seeing the Light
Working with the light meter
Use a gray card or object
Push shutter button halfway and reframe.
Exposure compensation overages the light meter.
for example, Sunny or snowy beach calls for +.5 or +1 compensation.
Beating backlight(3 possible methods)
The Digital Zone system
Exposure partners-ISO, Aperture and Shutter Speed
Relative to the human eye, the dynamic range of a CCD is very limited.
Three factors define the correct exposure: the sensitivity of the CCD, the strength of the light striking the CCD, and the length of time the CCD is exposed. The shorter the range of tones you have to work with, the more important it is to get the exposure right-to not overexpose the highlights or let the shadows block up.
Aperture and Shutter Speed
Aperture and shutter speed work together to control the exposure by determining how much light falls onto the CCD to make the picture. Think of the lens/aperture combination as a funnel, in which the big end is the lens(it gathers the light)and the small end is the aperture that controls how much light gets to the CCD in given period of time. In this analogy, the shutter is the valve that controls how long the light flows onto the CCD.
Aperture is measured in f-stops(the ratio between the focal length of the lens and the diameter of the opening in the diaphragm) and each stop in the standard series of stops represents a factor of two in the amount of light admitted.
Slow shutter speed effects
Aperture and Depth of Field
Aperture effects depth of field. The lens focuses only light from a certain distance onto the sensor, and depth of field is the measure of how much nearer or farther than that distance an object can be and still be acceptably sharp. The smaller the aperture, the greater the depth of field and the more of the photograph is in focus.The distance from the camera to the subject also plays an important role; close-ups have much more limited depth of field than landscapes do.
Depth of field is a function not only of aperture and distance from camera to subject, but of the focal length of the lens and the CCD size as well. The wider the lens, and the smaller the CCD, the greater the inherent depth of field the camera will produce.
A normal lens has an angle of view more or less like what you see with your eyes.
A wide angle lens has the effect of extending the field of visioninto the periphery and exaggerating the dens of depth. Telephoto lenses have a narrow field and give the impression of compressing distance.
Many camera have zoom lenses that allow a choice of working focal length. Because CCD's come in a variety of sizes, manufacturers usually translate their focal length into 35mm equivalents, with 50mm being normal, above 50 being telephoto, and below 50 being wide-angle.
Don't use a wide angle for portraits.
If you're doing macro work(extreme close-up), turn off the flash and use a tripod.
Modifying the light
Softer light has lower contrast, and shadows aren't so harsh, and portraits in these conditions are much more flattering.
You can soften the light by bouncing light into the shadows with a white board(foamcore) or a collapsible reflector. Or, you can look for a wall that is reflecting light. You could also diffuse the light by having the person sit under a large white piece of material or a tree to soften the light.
Flash is useful on sunny days to reduce contrast and fill shadows(fill flash). Also adds tiny 'catchlights' or specular highlights to a persons eyes(good).
Softening the flash with a third-party softbox or bounce system helps avoid blowing out the light areas of the image. Or, rubber band a white piece of paper to your flash and point the flash up.
Ways to reduce red eye