Canon EOS 350D / Rebel XT sensor
Many people assumed Canon would simply re-use the EOS-20D's sensor for the 350D,
but the company has developed an entirely new sensor for the budget camera. It's
an 8.0 megapixel CMOS design which measures 22.2 x 14.8 mm and delivers images
with 3456 x 2304 pixels. The sensitivity can be set between 100 and 1600 ISO.
In
contrast the 8.2 megapixel CMOS sensor of the 20D measures 22.5 x 15.0 mm and
delivers images with 3504 x 2336 pixels. In practice the fractionally larger sensor
of the 20D doesn't make any noticeable difference to the effective multiplication
of lens focal lengths which remains 1.6 times. The additional pixels of the 20D
sensor also make little if no difference to captured detail - see results section
later.
You'd therefore be forgiven for believing 8.0 versus 8.2 megapixels is purely
a marketing decision, but there's one important technical difference between the
two sensors. The 20D sensor can read data much faster, allowing it to deliver
a 5fps continuous shooting mode, whereas the 350D sensor's slower throughput limits
it to 3fps. This is still an improvement over the 300D's continuous shooting speed
of 2.5fps though, and the buffer has also been increased considerably - see later.
A quick note on pixel size and noise levels: the 300D employed a 6.3 megapixel
CMOS sensor measuring 22.7 x 15.1mm and delivered images with 3072 x 2048 pixels.
Clearly the individual pixels on both the 350D and 20D are physically smaller
which would normally raise concerns over increased noise levels. Canon has however
redesigned the pixels on both sensors so their actual photo-sensitive area is
bigger than their predecessors. As a consequence, noise levels shouldn't be compromised
- see results page.
Files and memory
Images can be recorded at three resolutions, each with the choice of two JPEG
compression levels. There's also an option to record a RAW file, with or without
a best-quality JPEG; unlike the 300D, this accompanying JPEG is recorded as
a separate file. Using the full resolution and best-quality JPEG setting, our
test image files ranged from 1.4 to 6.5MB, although the vast majority worked
out between 3 and 3.5MB each.
The 350D records images onto Type-I or Type-II Compact Flash cards and supports
FAT-32 formatting for those larger than 2GB in size; the slot can also accommodate
Microdrives. The camera sports a USB-2.0 port for copying images onto a PC or
Mac and comes with Canon's Digital Photo Professional software to process RAW
files.
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Image processing and handling speed
Behind the scenes the 350D's powered by the same DiG!C II image processor as
the 20D, 1D Mark II and 1Ds Mark II bodies. The image processor is a crucial
part of every digital camera, not just because of its impact on picture quality,
but also the speed with which data is handled in the camera.
As proved in Canon's higher-end bodies, the DiG!C II is a speedy operator, rapidly
processing raw data into JPEGs and keeping the shooting buffer clear for more
shots. The effect of the DiG!C II in the 350D is immediately apparent when it
comes to continuous shooting. As mentioned earlier, the 350D enjoys a slightly
faster continuous shooting speed compared to its predecessor - 3fps versus 2.5fps
- but it's the number of shots the camera can take before slowing down which
demonstrates the power of the image processor.
Canon officially quotes a buffer of 14 JPEGs on the 350D compared to just four
on the 300D, but depending on the subject matter it could actually work out
as many more. We framed our standard ISO 12233 optical test target with each
camera, set them to their best quality JPEG settings, then held the shutter
release, counting the frames until any bottlenecks slowed the shooting rate
or stopped it altogether. To ensure the CF card wasn't the limiting factor we
used a fast SanDisk Ultra II 1GB card.
The 350D fired off a respectable 41 shots in 15 seconds before it began to slow,
but even then, only by a small degree; it also seemed happy to continue shooting
at a respectable rate for much longer still. Each image measured an average
of 2.31MB, and after shooting 41 of them, it took just five seconds for the
camera to complete writing to the card.
The 300D performed in practice as it does on paper, firing four frames in roughly
a second and a half before slowing significantly. During the same period of
15 seconds, it captured just 13 JPEGs, each measuring an average of 1.98MB.
After letting go of the shutter at the 15 second point, the camera took a further
25 seconds to finish writing to the card.
Admittedly the file sizes produced above were slightly smaller than the average
day-to-day shots taken with each camera, but it still illustrates a big difference
between data handling on the two models. The older 300D almost stalls after
its four-shot buffer is full and takes an age to finish writing images to its
card. In contrast, the fast DiG!C II processor in the 350D clears its buffer
as you're shooting, allowing faster continuous shooting and for many more shots.
This processing speed extends to other areas of the camera including image playback.
Using the same ISO test image above, the 350D opened images in Play mode about
twice as fast as the 300D. Thumbnails were also much quicker, with nine images
on the 350D taking 1.8 seconds to load compared to over four seconds on the
300D. It doesn't sound that big a deal when written down, but feels very different
in practice.
The biggest difference of all in terms of speed though is the startup time.
This was an area where the older 300D could become infuriating, taking two or
three seconds before allowing you to take your first shot. It also took a similar
amount of time to wake up after the power-saving had kicked-in. Again this may
not sound like a big deal when written down, but this delay often proved excruciating
as opportunist compositions would sail off into the distance. This was one important
area where the Nikon D70 took the lead.
With the 20D, Canon brought a virtually instant 0.2 second startup time to it's
semi-pro range, and has now thankfully also applied it to the 350D. Starting
up, or waking up almost ten times faster than its predecessor could be enough
alone for many people to seriously consider the 350D - it's considerably more
responsive in every respect.
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