The stream of
technical data that is routinely dispensed in promotional literature
and by salespersons in photographic stores may appear daunting. This
article introduces the prospective buyer to some of
the hardware and software terminology that manufacturers and retailers use to describe the specification and performance
of imaging products.
the heart of all digital cameras (digital compact and digital SLR)
is an image sensor that employs solid state electronic processes to
record a scene. In nearly all mainstream cameras the image sensor is a CCD
(Charge Coupled Device)
or CMOS (Complementary Metal Oxide
Semiconductor) two - dimensional focal plane
that is typically
silicon based, though more exotic materials are used.
Today, CMOS image sensors that
added functionality and benefit from large
scale manufacture are achieving the performance levels of image
sensors founded on the
optimised CCD technology that has dominated the camera marketplace.
The camera lens focuses an image of the scene (primarily reflected
light) onto an image sensor comprising a mosaic pattern of light
- sensitive picture elements or pixels. The image sensor effectively
segments the image of the scene and generates data for the pixel
spatial location, called the pixel 'address' and the response.
response is proportional to the image related electronic charge that is released from silicon
(material) bonds and accumulates at the pixel 'address' for the
of the exposure, under the control of an electronic and/or
Electronic charge is accessed using
registers (systems of interline or frame transfer are typical) and
reduced to digital data that is passed to an electronic processor
(image processing engine) and then saved in a compressed
and/or uncompressed file format on a
removable memory card.
To preview/review images an integral colour LCD viewing screen that can
also display image data and control menus is provided. The description
is greatly simplified, though digital and film cameras share
components and features,
the digital camera offers much more. Once downloaded onto a
may be edited and manipulated, emailed,
online, exported to a database
or spreadsheet, ..., and integrated
into multimedia applications.
scale of excellence most used by manufacturers and retailers to
distinguish their digital cameras is the
pixel count. The
is the number of pixels that contribute to each image (some edge
pixels are unused). At the time of this writing, the effective pixel
count of low - end (point & shoot)
cameras is typically
8 MegaPixels, of mid - range (creative compact, SLR style, entry level
DSLR) cameras is typically 8 - 12 MegaPixels and of high - end (for the professional photographer market)
cameras is typically 14+ MegaPixels. Based simply on the pixel
point & shoot cameras
surpass professional cameras, though image quality is not the same.
Even though the pixel count continues to rise, understand that MegaPixel count is not the whole story (1 MegaPixel = 1 million
The effective pixel count may be specified differently, using an array
for example, my
Nikon D80 has 3872 × 2592 pixels, that means an image width of 3872 pixels
and an image height of 2592 pixels. Most cameras support
image capture at lower resolutions, for example, the 6 MegaPixel
camera may shoot at
1.5 MegaPixel resolution (this is useful for Powerpoint
presentations or web publishing) to save storage space on the memory
card. The baseline
criteria are not set in stone,
camera specifications change as a
result of demand driven technological innovation.
To create photo - quality prints
300 ppi (pixels per
inch) is the rule, however, this is printer/paper dependent, 200+ ppi
While the visual
differences in doubling the pixel resolution are modest, doubling
the pixel resolution does provide scope to recompose (crop
Notice that the displayed image
on the absolute pixel count, when displayed at 100%
a 1024 x 768 pixel image
a monitor screen set to 1024 x 768 resolution.
or sharpness of an image (sharpness is a subjective quality) is
determined by the pixel size (typically 2 - 8 μm, rectangular or square)
and the pixel count,
8, 12, 14+,
... MegaPixels, you can resize/downsample to capture an image at lower
resolution. Of course, for the same pixel count and fill -
(ratio of pixel (photosensitive) area to pixel area), larger/smaller
image sensors have larger/smaller pixels. For any image sensor
format, decreasing the pixel size
enables higher spatial sampling (higher resolution image capture). Naturally, there are
trade - offs, though smaller pixels can record more faithfully the
fine spatial detail (the change in brightness with distance) in a
scene, they are less sensitive to light, (compared to larger pixels, lower SNR at the same ISO).
As the pixel size is decreased,
the degrading effects of diffraction and photon noise
(fundamental limits) on image quality become more pronounced.
Furthermore, increasing the MegaPixel count necessitates a larger file
size, that lengthens the upload/download time.
is the ratio of the format width to the format height and
determines the relative dimensions of an image (photographic print).
These dimensions relate
to the image sensor active area
(that includes the pixels that contribute to each image).
A square has an aspect ratio of 1:1 or (1.00), the 35 mm
has an aspect ratio of 36:24 or (1.50), most compact camera formats
have an aspect ratio of 4:3 or (1.33). My Nikon D80 DX format camera
produces an image with
23.6:15.8 or (1.50) aspect ratio. Of
course, you can resize a
digital image (generate an image with any aspect ratio) using
image - editing software.
Traditional computer monitors have a 4:3 or (1.33)
aspect ratio. Widescreen computer monitors have
different (1.60, 1.85, ...) aspect ratios. HDTV has a 16:9
or (1.78) aspect ratio.
sensors used in consumer and prosumer digital cameras are listed.
FLM is the focal
length multiplier (see Depth of Field).
the relative shapes and sizes (approximate) of the image sensor formats.
|RELATIVE SIZE OF
Canon APS - C
field of view,
(FOV), or picture angle is the acceptance angle of light
from the scene and is determined by the focal length of the lens and the
dimensions of the field stop.
In the absence of a physical stop, the active area of the image sensor
(the linear dimensions) decides the extent of the scene that can
of view may be decomposed into horizontal (width) and vertical
(height) components. Using simple trigonometry, the field of view is given
SensorDimension is the horizontal or the vertical dimension of the
At close focus
distances, the denominator is replaced by 2FocalLength(M+1),
where M is
The image sensors used for digital cameras are different in size
(1/3", 2/3", ...) and type, there is no format standard
(unlike the standards for film).
Given a 20 mm lens, the
corresponding fields of view (relative to the diagonal) for 1/3" and
2/3" image sensor formats are 17.1° and 30.8°.
To demonstrate the field of view change with focal length,
consider a 28 - 300 mm telezoom mounted on a full frame DSLR
body (image format, 36 x 24 mm).
At the 28 mm limit the horizontal FOV is 2tan-1(36/56)
= 65.5° and the vertical FOV is 2tan-1(24/56)
At the 300 mm
limit the horizontal FOV is 2tan-1(36/600)
= 6.9° and the vertical FOV is 2tan-1(24/600)
Short focal length lenses (focal length shorter than the image format
diagonal) give a wide FOV that can
capture the broad extent of a
scene. An extended depth of field means that most foreground
in - focus. Short focal length
lenses appear to expand perspective and may distort near
Most cameras are supplied with a 28 mm equivalent lens for wide
sub full frame cameras, 12 and
15 mm ultra wide
angle lenses are available.
standard lens has a focal length of approximately the image
format diagonal and gives a FOV similar to the central FOV of the
human eye. For the 35 mm format the focal length of a standard
lens is 50 mm.
Long focal length 'telephoto' lenses (focal length longer than the image
format diagonal) give a narrow FOV
that can isolate and (magnify) the scene detail.
A restricted depth of field means that most foreground and background
features are not in - focus. Long focal
length lenses appear to compress perspective. Perspective is
determined by viewpoint not focal length.
The ISO equivalent speed is a measure of
the (camera) image sensor
to light. Like traditional film speed that is assigned a scale, ISO
25 (slow) to ISO 3200 (fast), at low ISO equivalent ratings the
image sensor is less sensitive to light, at high ISO equivalent
ratings the image sensor is more sensitive to light.
The ISO range 50 to 400
is typical for compact cameras (with smaller image sensors), the ISO range 200 to 1600
is typical for DSLR cameras (for some cameras the ISO range is
extended both lower and higher).
My Nikon D80 has an ISO range 100 to 1600 (high options, 2000, 2500
The freedom to select an appropriate ISO for each image
capture is a feature of digital cameras, however, noise (like grain
in film) can become objectionable
at high ISO ratings.
performance of digital cameras is a subject much debated. Sources of noise
may be classified
noise or non - sensor noise. Sensor noise includes dark current
(temperature dependent) noise, read noise associated with the signal processing
electronics and spatial (pattern noise variants) noise due to pixel to pixel non - uniformities associated with
the manufacturing process. The most significant
non - sensor noise is photon (shot) noise that determines the fundamental
limit on noise performance. Photon noise is present at
all times and best understood as a natural variation in the arrival
(and the subsequent detection) rate of photons (light) from the scene.
This is a property of nature, not a property of the camera.
In digital images, the above sources of noise are discernable as
luminance and colour variations (speckles). The significant noise
contributions (three noise regimes) are illustrated using the generic photon transfer curve.
The most fundamental measure of digital camera performance is the sensitivity or
signal to noise ratio (SNR)
that is dependent on the total noise (the sum of all sources of
noise). The sensitivity (SNR = 1) is limited by the total noise. For
high quality reproduction, the spatial
resolution and signal to noise ratio of digital images must be at least
'as good as' film images.
Photon noise and the full well capacity
(FWC) limit the maximum SNR that can be achieved, the FWC
is the maximum charge (measured in electrons) that each pixel can
store before saturation and is related to the pixel size. For most quality cameras, compacts and DSLRs, the noise performance is
limited by photon statistics (photon noise is proportional to
the square root of the average number of photons). At pixel level,
photons are converted to electrons,
SNRelectrons = √η
= √N, where the conversion factor
η is the
(η < 100%) and N is the average number of photons. On condition that
noise is not visible, electronic gain to increase the ISO rating
(like pushing film) may not significantly degrade the image quality.
The maximum ISO rating (highest sensitivity) is determined by the
noise performance and the lowest SNR
that is practical. By careful design of circuitry and optimisation,
one or two sources of noise dominate
the noise performance.
Even so, compact cameras and DSLR cameras do not
routinely offer the same image quality for the same pixel count.
In general, compact cameras have smaller image sensors and smaller pixels. Typically,
smaller pixels have smaller FWCs, have
lower SNRs and
a reduced dynamic range.
The term dynamic range (the ratio of the FWC to the noise floor,
characterises the capability of a digital camera to record the
darkest and lightest (black to white) regions of a scene.
light levels, photon noise is the limiting factor, at low light
levels and for
long exposures, read noise and dark current
noise are the limiting factors.
Typically, the SNR of high - end DSLR cameras
(FWC ≈ 50,000+e @ ISO 100) is
more than 3x the SNR of low - end compact cameras (FWC ≈
5,000+e @ ISO 100). High fill - factor, low cross - talk image
sensor designs using novel pixel structures and microlenses can enhance the sensitivity.
Adding the charge from
neighbouring pixels, binning, can increase the signal to noise ratio,
but lowers the resolution.
However, the strengths and weaknesses of digital cameras are only
revealed by spatial frequency domain analysis of a range of
Today, some digital cameras
achieve the imaging and performance standards
(similar noise and resolution figures) of film cameras (understand
that image quality is subjective). Nonetheless, be aware of
unrealistic performance claims (especially for compact cameras
small format image sensors) that
appear to challenge basic physical principles.
For low light photography, both indoors and outdoors, higher
sensitivity guarantees faster shutter speeds (to freeze motion for
sports photography) to reduce the loss of definition due to
camera and subject movement. Furthermore, higher sensitivity may circumvent the need for flash
illumination, so that images appear more natural. At higher
ISO ratings, because fewer photons are collected for a correct
exposure (and electronic gain introduces noise), the
corresponding SNRs are lower. Look for cameras that provide a noise
reduction setting at higher ISO ratings (long exposures in
low light conditions), where (at large print
sizes) digital noise can become unacceptable. To minimise
luminance and colour noise, noise reduction
software is available as a stand - alone package or compatible plug - in for
the popular image - editing applications.
In most digital cameras the image sensor is fabricated using silicon
microelectronics technology. The image sensor is responsive to the
broadband scene luminance and cannot distinguish colour. The
spectral response of silicon extends from about
0.35 - 1.10 μm (1 μm
= 1/1000 mm), beyond the region of the electromagnetic spectrum
that stimulates the human visual system (0.4 - 0.7 μm).
cameras include a short pass filter (hot mirror) to remove the near - infrared
component of the scene luminance.
Use a TV remote control to check the infrared response of your camera. On condition that you can access the long
wavelength response (about
0.7 - 1.1 μm), infrared photography
Remember, this is reflected solar energy, not self - emitted thermal
To prepare your camera for infrared photography
attach an IR filter (Hoya R72, Wratten 88A, ...) that is opaque to
visible light. Use the
camera self - timer and a robust tripod, long exposures are typical.
An alternative approach is to modify the camera, the IR short pass
filter is replaced by an IR long pass filter, and the autofocus is
fine - tuned to compensate for the focal shift. Several companies can provide this specialist service.
The NIR reflectance of familiar subjects is variable, foliage has a
high reflectance, water has a low reflectance. To finish, create a
monochrome image of contrasting tones (even colour images) using an image - editing
A complete treatment of infrared photography is given in a
Any perceivable colour is a mixture of the primary colours
suitably combined. For the reproduction of colour most digital
cameras use a Red, Green and Blue primary colour filter that is
registered (in a repeating sequence on the face of the image sensor)
with each pixel. Each pixel is responsive to only one colour. The
colour filter is configured as
a 2 x 2 array of one Red, one Blue and two Green
filters (the human visual system is most sensitive to yellow -
green light) to capture 25% of the red light, 25% of the blue light
and 50% of the green light. The mosaiced
image data from an 8 MegaPixel camera consists of 2 MegaPixels
2 MegaPixels filtered blue and 4 MegaPixels filtered green.
Given that one primary colour is recorded at each pixel address,
CMOS image sensor captures three
the resolution and sensitivity are reduced by factors of 4 and 3 (compared to the panchromatic (B&W) image),
however, spectral interpolation (to recover the omitted colour channels, the demosaicing algorithm
combines the RGB responses from neighbouring pixels)
is used to
reconstruct the full colour image. There are many demosaicing
techniques using non - adaptive or adaptive, hardware - software
interpolation. Interpolation is a mathematical technique used to
estimate unknown data values from known data values, within the
range of the known data values.
The most common implementations of the demosaicing algorithm use bilinear
or cubic B - spline interpolation. Of course, there are trade - offs between colour fidelity,
and image defects. RAW capture allows you to post process (on your
PC) using more sophisticated demosaicing
algorithms that introduce less errors.
Alternative colour filter configurations are the CYGM
(Cyan, Yellow, Green, Magenta), the RGBE (Red, Green, Blue, Emerald)
and the RGBW (Red, Green, Blue, White).
In a discrete sampling process, erroneous data (aliased data) may
appear unless the signal is band - limited, consistent with the
Shannon theorem. For cameras that use a colour filter array, moiré patterns and colour artefacts are sometimes evident. Most digital cameras use an optical low - pass (anti - aliasing) filter
(based on birefringent crystal polarisation or phase delay) placed on top of
the image sensor to (slightly) blur the image and remove the high
frequency content, thereby exchanging sharpness for reduced
aliasing. Some cameras use an optical filter and image processing software. Most image - editing software packages
anti - aliasing
tool that can reduce the most distracting artefacts.
There are many optical techniques for colour separation, most
consumer and professional (compact
and DSLR) cameras employ some variant of the Bayer colour filter
(lateral colour filter). The pioneering
non optical capture technology developed by Foveon is based on solid
state electronic processes.
To produce full colour
non - interpolated imagery, the
colour channels (100% of the light) at each pixel address
using Red, Green & Blue photosensitive layers embedded at the
absorption depth of
the primary colours, similar to a film emulsion (vertical colour
filter). Furthermore, the demosaicing process and the separate anti - aliasing filter are unnecessary.
The Sigma SD1 DSLR uses an APS - C X3 image sensor.
Most cameras convert the response to light (scene luminance) from
analogue form to digital form,
typically 8 - bit data that corresponds to a tonal range of 256 (28)
levels on a scale from 0 (Black) to 255 (White). For photographic
quality full colour images the three colour channels are
coded as 8 - bit data (bit (colour) depth of 8)
to produce composite 24 - bit colour, about 16.7 million hues, more
than the human eye can distinguish. Some high - end cameras use 48
- bit or 36 - bit colour palettes,
images are pre - processed
and downsampled to 24 - bit data.
is a graphical representation of the distribution of tonal values
(number of pixels of a given brightness)
that can be used to optimise the camera
and for post production. Learn how to interpret the image
(all DSLRs display a histogram, some compacts display a
live histogram and some
high - end cameras display
separate R G B histograms). For an image that has no major
highlights (image highlights flash on the LCD screen) or shadows the distribution of tonal values
(mainly mid - tones). For a high - key image, the distribution is displaced to the right
(toward lighter tones), for a low - key image, the distribution is
displaced to the left (toward darker tones).
All scenes are different, all image histograms
are different, there is no 'ideal' image histogram.
typically 1/3 stop increments,
(−ve) to darken an image that is clipped on the right,
to lighten an image that is clipped on the left. Modern cameras can
analyse the scene dynamic range (the difference between the lightest
and darkest regions of an image) to
optimise the distribution of tonal values. Of course, histogram
manipulation is possible using image - editing software.
The spectral power distribution of a light
source that determines the visual appearance can be described by a colour temperature
that is measured on the Kelvin temperature scale.
record coloured and white objects as perceived by
the human visual system (under
all lighting conditions), the camera has to perform a
that adjusts the image sensor RGB reponse.
The process ensures colour correctness and that objectionable colour casts are
cameras provide an automatic white balance (AWB) and presets for
the common lighting conditions,
Direct Sunlight, Fluorescent,
Flash (names vary). The white balance presets are
selected using a button and dial, or multi - selector,
typically an icon is displayed on the LCD panel.
To manage unique lighting conditions (mixed lighting, ...) use the
white balance setting to record a white balance under the same lighting conditions.
Useful features on some advanced cameras are white balance bracketing
(allowing you to capture a sequence of images with colour temperatures
slightly lower and higher than the preset)
and fine tuning.
There is an air of mystery
associated with white balance
(the concepts are not intuitive), trial and error is the best approach to gain an
colour temperature for several artificial and natural light sources are listed (see
Most cameras have both digital and optical zooms. The
zoom provides an apparent increase in focal length by means
of software to perform an upsampling operation. Lens elements do not move. Using an image
interpolation algorithm (similar to the image enlargement software
on your PC), the central part of the image is magnified
to produce a cropped
image at full resolution but of degraded quality. Though in - camera
processing is applied before JPEG compression, typically, upsampling
artefacts and more subtle image defects are visible. To preserve image quality, some cameras
feature an 'intelligent' zoom
function that obviates interpolation. The digital zoom specification
a secondary consideration.
optical zoom lens,
either built - in (telescoping) or interchangeable,
has a variable focal length that changes the field of view and
the true magnification as the lens is zoomed. The optical zoom specification should be a primary
consideration. The focal length of a super zoom may change from 28 mm (wide angle)
to 300 mm (narrow angle) plus. Optical zooms are ideal for general
purpose photography and useful for scene composition from a set
location, zoom ratios (the ratio of longest to shortest focal
length) of 10:1 and more are commonplace. To achieve high zoom
ratios there must be design compromises, do not expect the optimal
for the entire focal range.
For basic (Point & Shoot) cameras a 3x
optical zoom is typical, (for example,
38 - 114 mm equivalent). Digital and optical zooms can be
operated alone or
combination. A 3x digital zoom coupled with a 6x optical zoom
has an 18x zoom range.
The focal length and field of view of a prime (non - zoom) lens are fixed.
As a general rule a prime lens provides superior performance.
Though 'older' interchangeable lenses were mass - produced
for 35 mm (film) SLR cameras, most can be used effectively with
digital bodies. Even so, some lenses have been re - engineered for
digital and film cameras. Today, lenses that are designed exclusively for digital
SLRs (the APS - C image sensor format includes Canon EF - S,
Nikon DX, Pentax DA, ...) have matched image circles and optimised coatings to reduce vignetting (shading at
the corners of an image) and flare and enhance
sharpness. It is not only DSLRs that benefit, many compact cameras
can accept a telephoto and wide angle adapter to extend their focal
Image stabilised lenses (on some cameras, the image
sensor has 'built - in'
anti - vibration mechanisms (move lens elements so the image at the focal plane
to compensate for camera
The practical benefit is up to 2 - 3 stops compensation (slower
shutter speed) for image blur (allowing the lens to be closed for
greater depth of field). Bear in mind, image stabilisation
compensates for the image blur due to camera movement,
not subject movement.
The integral electronic flash unit has several
modes of operation that provide some control of the ambient
lighting. The standard modes are
auto flash, fill - in flash
High - end cameras offer more advanced flash features.
No flash is
the default setting.
- Auto flash:
the camera on - board computer estimates the available light and
need for the flash.
- Fill -
in flash: used for a back or sidelit subject, to even the
illumination (reduce contrast), remove unappealing shadows from
foreground subjects and create catchlights.
- Red - eye reduction:
a pre - flash that causes the eye pupil to close
(the pupils are dilated in low light) so light that is reflected
blood vessels/pigment in the retinal layers of the eye
(primarily the choroid) is
reduced. This feature is useful for animal (green eye) and
- High - end
cameras may offer dedicated flash modes, front and rear curtain
sync and slow sync for more creative photography. Using multiple
flash you can create a time sequence of images.
The flash guide number,
GN (f/# x distance) is a measure of the power output
particular ISO setting (usually ISO 100) and is used to determine the
working distance for a correct exposure at a given aperture. The
more powerful the flash (higher guide number),
the greater the
working distance, remember, for a point source the illuminance is
governed by the inverse square law. The flash hot shoe (synch
terminal) is used to connect an external flash unit (the integral
flash is disabled) for added illumination. You can use gelatin
correct the colour temperature of the flash unit light. Off - axis flash units
can reduce many undesirable optical effects such as background
shadow and red - eye. To remove red - eye, use
in - camera software (some cameras can correct images) or image -
Image File Format
Image files can
be saved to
Compression routines are described as lossy or lossless, dependent
on the image data that is discarded.
The standard file formats for digital cameras are:
Photographic Experts Group), is a compressed lossy
universal format that is ideal for continuous - tone
images. The JPEG format (the original standard) is used by
nearly all digital cameras and is identified by the (.jpg file
extension). The JPEG image compression standard uses
discrete cosine transform coding.
Always post process your JPEG images in an
benefits from higher compression ratios, flexibility,
selectivity and superior image quality and is identified by the
(.jpg2 file extension).
The JPEG2000 image compression standard
uses advanced wavelet transform coding.
is unprocessed data from the image sensor. My Nikon D80 uses a
12 - bit
image processing engine (compressed NEF).
For RAW capture, the image data
and camera settings are separated for versatile post production. Most cameras can
record RAW and JPEG files (RAW + JPEG) simultaneously.
On your PC, convert RAW files to JPEG, TIFF or PNG
(Portable Network Graphics) files.
(Tagged Image File Format) is an uncompressed format that is suitable for
desktop publishing applications and archiving digital images
(the industry standard).
Though write times to the memory card are long, LZW lossless
(no quality loss) compression reduces the file size. The
TIFF:JPEG High Quality
file size ratio is about 3:1. Many cameras do not support the TIFF format.
The table compares JPEG and RAW
The files are
compatible with all standard image - editing
software and internet applications.
files are not compatible with most standard image - editing software.
There is no standard format for RAW image files,
common proprietary formats are, Canon (CRW), Nikon (NEF), SONY (ARW).
software is used to read and edit files. Some third -
party image - editing software can read RAW files.
Using image - editing software limited enhancement
options are available post capture.
Image data and
camera settings are separate.
Using image -
editing software unlimited enhancement options are available
capture, colour (brightness, hue and saturation),
sharpening and white balance.
Highly versatile, most
camera settings can be changed.
small file size allows a large number of images to be
stored on the memory card. Fast write times. The
compression ratio can be adjusted to trade
size. Most cameras offer image quality and size options.
The large file size,
smaller than TIFF, allows a small number of images
to be stored on the memory card. Slow
Some loss of image quality.
JPEG - FINE is ideal for home - use. Multiple saves
result in a progressive loss of image quality. To retain
image quality, process images in the TIFF format.
No in - camera image processing.
No loss of
Digital cameras store (and exchange) captured image data on a removable memory
card. Once the image data has been downloaded to your computer or
peripheral storage device
(portable hard drive) clear the memory card for reuse.
memory cards are
Compact Flash, Memory Stick, MultiMedia,
Secure Digital, Smart
xD - Picture.
Some cameras provide slots that accept two (different) memory
(PCMCIA card) is a
card and adaptor that is inserted into the PCMCIA bay on your
computer, (on most laptops). Less fashionable is the small (CD - R)
disc. The storage capacity of memory cards varies greatly, some
professional cards can store up to 32 GB of data (at the time of
this writing). Though high capacity memory cards (indispensable for
high resolution cameras) are useful, never forget, your memory card
can become corrupted and data can be lost. Today, there is image
retrieval software to recover damaged images.
A larger memory card
available in Type 1 and Type 11 variants. The card is rugged and
versatile. The Type 11 card has the same dimensions as the IBM Microdrive
(miniature hard drive). The preferred card for many professional SLRs.
At the time of this writing, the capacity is up to 16GB.
(Duo, PRO Duo)
A small memory card developed by SONY and compatible
with other SONY audio visual products. Standard - size
adaptor. Integral erasure prevention switch. At the time of
this writing, the capacity is
up to 8GB.
memory card, smaller than Smart Media.
Integral erasure prevention switch.
Slower speed than secure digital. At the time of this writing, the capacity is up to 1GB.
Many compacts use the SD card.
SDHC variant. Integral erasure prevention switch and
security functions. Fast speed. Used in audio visual products. At the time of
the capacity is up to 8GB.
A large memory
card but smaller/slimmer than a CompactFlash
Gold connections on one edge. At the time of this writing, the capacity is up to
xD - Picture
Fuji/Olympus co - developed. A
very small memory card,
postage stamp size.
Fast speed. At the time of this writing, the capacity is
up to 2GB.
Below is a ballpark guide to the number of images
(JPEG Fine - Large) that
memory cards of different capacities
can accommodate (the image quality and image size that you select determine the file
| Pixel Count
card speed 20x, 40x ... is a measure of the rate of data transfer (20x =
3MBps) to (remove data from the buffer) or from the memory card.
Unless you require to capture many images in rapid succession, speed
is not a critical factor.
images saved to a JPEG format, the camera may offer
quality (fine - basic) and image size (large - small) options,
dependent on the in - camera processing. Selecting the fine/large
option for all your photography has a downside, larger file sizes that
place more demand on the memory card capacity. For web and
email applications, select the basic/small option to maximise storage.
The table lists the image quality options (and the data compression
applied) for Large, Medium and Small image sizes on my Nikon D80.
To archive your digital image collection, use CD - Rs (the storage
700 MB) rather than DVDs, should the media malfunction, the
loss is less painful. The life of a CD - R is several tens of years
and for archival quality media, even longer.
standard connections and ports used to transfer image data to a
computer hard drive
or peripheral device are
names, IEEE 1394, iLink),
System Interface, pronounced 'scuzzi') and
(Universal Serial Bus).
The speed of data transfer is measured in units of megabytes per second (MBps).
serial interface that comes in several variants. Data transfer of up to 50 MBps for Firewire 400 and
100 MBps for FireWire
800. Used on high - end cameras and camcorders.
An older interface
with four speed options. Data transfer speeds vary from
5 MBps for the original standard, to
40 MBps for the current (Ultra 2) standard.
Not so user -
The original standard
interface. For the earlier standard, data transfer is up
to 1.5 MBps. Hot swappable.
The latest USB variant
is faster and backward compatible. For the fastest
standard, data transfer is up to 60 MBps.
friendly. Hot swappable.
To transfer (download) images to your computer hard drive use the (proprietary)
software supplied with the camera (most operating systems can
recognise cameras) or connect a dedicated or multiple format
card reader to your computer by means of Firewire or USB 2.0 cables.
A card reader places no demand on
the camera battery and the download time is typically much faster.
Once the transfer is complete use the camera to clear and reformat
the memory card. You can also use a memory card adapter that slots
into the PCMCIA bay on your computer.
Wireless communication between compatible devices is available for
are equipped with Bluetooth, Wi - Fi or Infrared
(IrDA) - transceiver/software to send and receive radio or infrared signals.
In addition to the (in - camera) algorithms that control image
capture, image transfer, printing, ...,
image processing software
is included to enhance and optimise images. While automatic
optimisation is normally adequate, (subtle and more obvious) changes
are possible by means of options that are accessed using embedded menus:
mode (sRGB, Adobe RGB)
(normal - enhanced), the hue 'undiluted' by white
Sharpening (normal - high)
Most digital cameras are packaged with proprietary image - editing
and file browser/organiser software (file management becomes a
major issue as your image library develops), that uses
keywords/tags to access and catalogue images.
For cameras that save to a proprietary RAW file format, RAW
(often extremely basic, when supplied free with the camera) is
available from the manufacturer that allows you to apply different
camera settings (colour, sharpening, white balance, ...). For my
Nikon D80, there is Nikon Capture NX.
Though some RAW files can be read by the popular image - editing
applications, plug - ins
(add - on software used to extend functionality) may be
necessary. There are many suppliers of compatible plug - ins for the
popular image - editing applications.
Digital cameras store EXIF METADATA (EXIF - Exchangeable Image File
the standard format),
embedded data that provides a record of the camera settings (Aperture,
Exposure, Format, ISO, White Balance, ...) for each image.
newcomers with an enthusiasm to develop photographic skills,
METADATA is a useful learning tool, retrieve the metadata to see the effect of different camera settings
on your images.
Images can be printed directly, (no PC required), using digital
cameras and printers (inkjet, dye - sublimation ...) that are PictBridge compatible. PictBridge
is the standard for direct printing, look for the logo.
The major claims on the battery capacity are previewing (live
composing) and reviewing images on the LCD screen, using the
integral electronic flash unit and using the autofocus: super zoom
lenses in particular have a sizeable power demand. For digital
cameras that use CMOS based components and devices, the power
profile is typically low and the battery life is extended. On most cameras the battery condition is indicated by
on the LCD panel.
For most digital cameras the power resource is a rechargeable Li
- ion (Lithium Ion) or NiMH (Nickel Metal Hydride) battery,
both are durable and can support several hundred (some 1000+) image
captures. Alternatives are the Li
and the NiCd
(Nickel Cadmium) battery that is based on older technology.
My Nikon D80 uses a rechargeable Li - ion battery that has a fast recycling time and for backup power, CR2 lithium
For photographic holidays, carry a spare proprietary battery or bolt
- on battery pack. Non - proprietary AA and AAA NiMH batteries
memory effect) are
available off - the - shelf, are environmentally friendly (unlike NiCd
is toxic) and compared to alkaline batteries, have superior endurance.
Bear in mind, for different battery types (Alkaline, NiMH,
the voltage stability throughout the discharge cycle may not be the
The higher rated batteries, (mAh (Milliamp Hour) is a
measure of the capacity) are longer lasting. A 1000 mAh battery can
deliver 10 mA for
100 hours (or 100 mA for 10 hours). The unit of capacity is mAh, (I
x t), where
I = current, t = time. Since energy E = V x (I x t),
for a given voltage, V, E is proportional
to mAh. Sometimes
the capacity is quoted in Wh (Watt Hour), to
convert, Wh = V x mAh /
electricity supply is billed in kWh (Kilowatt Hour).
Batteries should be changed in sets and
never mixed. During extended periods of photographic inactivity,
remove the batteries from your camera. Store batteries in a cool dry environment
(water can corrode) and do not expose
to direct sunlight.
are a battery charger (with 12V DC car
adapter) and power inverter.
For users of digital cameras, the efficient management of battery power is
a major issue.
In general, the low - end (point & shoot) cameras are compact,
lightweight, inexpensive and offer basic features, the mid - range
cameras (creative compact,
SLR style and entry level DSLR) and high - end DSLR
cameras are less compact, heavier, increasingly more expensive and offer advanced features.
Whether you are a newcomer to digital (and want to infuse new life
your photography) or thinking of upgrading your
digital camera, before you purchase, ask two fundamental questions:
do I want the camera to produce large prints, then, the resolution
may influence your buying decision, recall
the 300 ppi rule, (the professional print standard). To create photo
- quality 8 x 10 inch prints a 7.2 MegaPixel (2400 x 3000) camera is recommended.
However, this is printer/paper dependent, 200+ ppi is often
do I want the camera for general or specialised (macro, sport,
wildlife, ...) photography.
The answers should enable you
to decide on the specific features that best suit
features to look for:
The camera should have
a near instantaneous startup, so that unforeseen
photo - opportunities are not missed.
auto focus should operate quickly (no autofocus lag) and
silently, even in low light conditions. Most cameras have multi
point autofocus and some feature predictive autofocus that tracks a subject
There should be no
shutter lag, so that passing photo - opportunities
are not missed.
should provide programmed scene/shooting modes (from day one you can
use the camera).
The camera should
provide some creative photographic controls.
The camera should
have an easy to view (anti - glare, wide viewing angle), high
resolution LCD screen. On some cameras the LCD can tilt to
composition from an inaccessible viewpoint
high - angle shots, ...).
For cameras that
use interchangeable lenses, there should be a range of compatible lenses
(forward and backward compatibility) and upgrades.
camera, test the electronic or optical viewfinder, convince
yourself that on - screen menus are easily navigated and all the camera controls are user - friendly.
innovative features that may be useful at once or maybe later,
picture recording, noise reduction, high
sensitivity, built - in image stabilisation, dust removal
face detection technology,
DSLR live view technology, ...).
capture several test images, both indoor and outdoor,
that you can review on the colour LCD screen
images and text © imajtrek