Canon EOS Digital Rebel XT SLR Review
By Movable Type Admin
Camera Design and Features
The EOS Digital Rebel camera is not a chunky camera by any means and no one has suggested that it was in need of a diet. By comparison, however, the EOS Digital Rebel XT camera is considerably smaller. From a distance, the XT is stylish and compact; in hand, it is delightful. Compared with its predecessor, the width of the XT is 15.5 mm smaller; the height is reduced by 4.8 mm and the thickness of the body is 8.4 mm less. The weight has been reduced by 2.5 ounces/70 grams. The body alone weighs 17.1 ounces/490 grams With a battery, a CF card and the EF-S 18-55mm standard zoom lens, the camera weighs just 1.5 pounds/720 grams.
The body consists of a chassis made of stainless steel, and a mirror box made of high- strength engineering plastic. The mirror box, to which the lens mount and image sensor are attached, is fixed very securely to the chassis to obtain the same body strength as the EOS 20D. This helps prevent the flange focal distance from changing due to the static pressure of the attached lens.
As with the EOS Digital Rebel model, the EOS Digital Rebel XT camera's top, front and rear
covers are made of special engineering plastic known for light weight, excellent strength
and electromagnetic shielding: ABS resin, polycarbonate resin, and polycarbonate mixed
with special conductive fibers. The exterior finish is more refined than the EOS Digital
Rebel camera's. The Canon logo is now embossed and colored to give the XT a high-quality
appearance. Both titanium silver and satin black body colors will be offered.
The Digital Rebel XT features Canon's 8.0 Megapixel CMOS (Complementary Metal Oxide Semiconductor) sensor, which captures images of exceptional clarity and tonal range and offers the most pixels in its class. This APS-C size sensor (22.2 x 14.8mm) has the same 3:2 ratio as film cameras, creating an effective angle of view that is 1.6x the normal EF Lens focal length. Featuring an on-chip Noise Reduction Circuit with an expanded ISO range, this sensor offers professional image quality in a consumer digicam.
Several engineering features account for the sensor's wide ISO range (100 to 1600), low noise, high dynamic range, and low power consumption. The configuration of each photo diode in each pixel has been optimized; detail processing has been improved, and a greater portion of each pixel is now sensitive to light. The microlens array which gathers light for the sensor has a new design, shared with the microlenses in the EOS-1Ds Mark II, 1D Mark II and 20D that reduces the gaps between the lenses. This narrow-gap array gathers light more efficiently and loses less light between the lenses.
The new, 3-layer optical low-pass filter has the same construction as the EOS 20D's filter, an infrared absorbing glass and three crystal plates having different optical axes. A dichroic mirror with a dielectric, multi-layer coating on the front surface deflects light over a wide range of infrared wavelengths. There is also an infrared- absorbing glass layer to absorb nearinfrared wavelengths in the visible spectrum.
The low-pass filter incorporates two monocrystal plates that separate the subject image into four horizontal and vertical directions. Between these two plates is a phase plate, also monocrystal, which converts the linear polarized light into circular polarized light. The first crystalline plate separates the image into two images horizontally. The linear polarized light is converted into circular polarized light by the phase plate. The second crystal plate separates the images vertically, resulting in four duplicate images arranged in a square matrix. The image separation in the horizontal and vertical directions is optimized for the sensor pitch so that false colors and moir� caused by minute horizontal and vertical lines in the subject are reduced while resolution is actually increased. Additionally, this hybrid construction, with its deflecting and absorbing layers, reduces image fogging and red ghosting caused by sensor reflections.
The CMOS sensor features a second generation, on-chip, noisereduction circuit that
includes a new low-noise gain amp and an offset reduction circuit. The signal is
amplified in slow-read steps. The result is the effective elimination of random noise and
fixed pattern noise. With the EOS Digital Rebel XT camera, one can even photograph the
heavens in the night sky with very low noise.
EF Lens Mount
The EOS Digital Rebel XT uses a Canon EF lens mount (full electronic control type)
and accepts the over 50 available Canon EF lenses from 14mm ultra-wide-angle to
1200mm super-telephoto including the new EF-S type.
Available only in the Digital Rebel XT kit, Canon's compact EF-S 18-55mm f/3.5-5.6 zoom lens approximates a 28-90mm zoom lens (in 35mm format). By reducing the distance from the rear of the lens to the imaging sensor and reducing the size of the image circle to accommodate the camera's imaging sensor size, the lens produces high image quality with superb resolution at all focal lengths. The lens is also smaller and lighter than conventional lenses because of the shorter backfocus distance.
Utilizing a 7-point autofocus system the Digital Rebel XT is capable of analyzing where a subject is -- even when it is off-center - and almost immediately bringing it into focus. It can also analyze subject movement and automatically select locking or tracking AF modes as needed. These features simplify the camera's operation and optimize its performance. The Digital Rebel XT allows users to select locking or tracking AF modes independently, adding a new dimension of creative control. The DIGIC II chip actually help increase the speed of autofocus calculation and hence the responsiveness of the autofocus itself.
The Digital Rebel XT has three user selectable autofocus modes: One-shot AF, AI Servo AF with focus prediction and AI Focus AF as well as manual focus. Going from autofocus (AF) to manual focus (MF) is accomplished by flipping a switch on the lens itself. The AF system is able to work down to 0.5EV at ISO 100.
The AF-assist beam is a series of stroboscopic flashes from the builtin flash or a near-IR
patterned LED with a compatible accessory Canon Speedlite. With the built-in flash, the
working range of the AF-assist beam is approximately 4 meters/13.2 feet at the center
and 3.5 meters/11.5 feet a the other 6 AF points. Firing stops when the focus detection
confirmation signal is detected.
E-TTL II Flash
The camera's high profile, built-in retractable flash unit makes taking pictures with well-balanced foreground and background exposures simple thanks to Canon's E-TTL II (Evaluative Through-The-Lens) flash exposure metering system. When shooting in the AUTO mode or the Basic Zone modes (except landscape, sports or no flash mode), the built in flash will automatically pop up and fire in low-light or back lit conditions. In other recording modes you press the release button to pop it up when needed. The recycling time is only three seconds.
E-TTL II takes effect when the built-in flash or an accessory EX-series Speedlite is used. E-TTL II does not assume that the AF point in use covers the main subject. Instead, when the shutter button is pressed completely, ambient light is measured just before a pre-flash fires. For each metering zone, the ambient reading and the pre-flash reading are compared.
Areas having a large difference between ambient and pre-flash readings are selected
and analyzed. Extreme differences suggest a highly reflective or specular object; these
areas are eliminated from calculations, avoiding underexposure. When a lens
providing distance information is used, this data is also considered in determining
the presence and location of a high-reflectance object. The selected pre-flash
readings are added and averaged and the output of the main flash is calculated. Even
if the subject changes position, reflectance or size, the flash metering remains highly
accurate and stable.
Some other highly useful changes to the flash system of the EOS Digital Rebel camera have occurred:
The eyelevel viewfinder shows approx 95% of the captured image with 0.8x magnification via a pentamirror with a fixed focusing screen. There is a builtin -3.0 - +1.0 diopter adjustment. Around the viewfinder is a soft rubber Ef frame that fits comfortably against your face or eyeglasses, it provides a 21mm eye point.
Canon offers E-series Dioptric Adjustment Lenses (from -4 to +2 values), the
Angle Finder C for 90° viewfinder applications, the EP-EX15 Eyepiece Extender
and replacement Ef rubber frames.
Inside the viewfinder are seven focusing points, the active focus point(s) are
illuminated to indicate which AF zone(s) are selected. Viewfinder information
includes - AF information (AF points, focus confirmation light), exposure information
(shutter speed, aperture value, AE lock, exposure level, AEB in progress, exposure
warning), flash information (flash ready, red-eye reduction enabled, red-eye reduction
lamp on, high-speed sync, FE lock, flash exposure compensation), maximum burst, CF card
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