Canon EOS-1DSCanon extends the EOS-1D with 11.1 megapixels, and a full-frame CMOS sensor!<<Viewfinder :(Previous) | (Next): Exposure & Flash>> Page 5:OpticsReview First Posted: 9/24/2002 |
Optics
Sensor
One of the first notable characteristics of the EOS-1Ds's optical system is
its unusually large CMOS sensor. The chip on the 1Ds measures 35.8 x 23.8 millimeters,
almost exactly matching the standard 35mm film frame size of 36 x 24mm. This
is a very significant development, because it offers photographers with Canon
lenses the opportunity to shoot true wide angle digitally for the first time.
(Because the sensor is the same size as a 35mm frame, there's no "focal
length multiplier" caused by the sensor's cropping of the 35mm image area.)
For the first time, a 16-35mm zoom behaves like a 16-35mm zoom, rather than
the roughly 20-44mm equivalent focal length range that lens would have on the
original 1D.
The EOS-1Ds' sensor has a total of 11.4 million pixels. Of these, 11.1 million are "effective" pixels, the rest being lost to dark current calibration and edge effects around the periphery of the array. After processing, the resulting images measure 4,064 x 2,704 pixels at full size, or 2,032 x 1,352 at half-size. This is a new high for Canon, although as I go to "press" with this review, word has already leaked of a full-frame 13.9 megapixel camera by Kodak, using the Nikon F-series lens mount.
Lenses
The EOS-1Ds features a Canon EF lens mount, which accommodates the full range of Canon EF lenses. I normally cite the aperture and focal length of a digicam's lens in this part of the review, but because the EOS-1Ds accepts a wide range of lenses, these characteristics will vary depending on the lens in use. My evaluation model was accompanied by Canon's 100mm Macro lens with a maximum f/2.8 aperture setting.
Antialiasing Filter (?)
Essentially all of today's digital cameras use "antialiasing" filters in front of the sensor array to reduce color aliasing in images containing high spatial frequencies (high-contrast, closely spaced lines). These filters work by slightly blurring the image -- technically, by knocking off the high spatial frequencies, while hopefully leaving the lower frequencies undisturbed. The problem of course, arises in trying to balance the need for antialiasing with the desire to maintain good image sharpness. Too strong a filter produces soft-looking images, while too weak a filter results in color "twinkles" and "jaggies" appearing in the fine details. Some high-end cameras leave the choice up to the user, with a removable antialiasing filter that allows the user to choose whether or not to use it, based on specific shooting conditions.
Canon claimed to have taken a different approach with the original 1D, deliberately choosing an antialiasing filter with a higher cutoff frequency, and relying on fancy image processing to eliminate or reduce any aliasing that might creep in as a result. How well does it work? It's a little tough to say, as differences in sharpness and detail can be so subtle between cameras. Compared to other 4-megapixel cameras I've tested, it did indeed seem to deliver about as much detail as any of them, and also displayed an absolute lack of color artifacts and aliasing in my resolution target shots.
At press time, I didn't know whether Canon had employed the same antialiasing technology in the 1Ds or not, but I can attest that it likewise showed virtually no color aliasing in the resolution target images.
Autofocus
The EOS-1Ds employs a fast autofocus system, with a myriad of focusing options. At the heart of Canon's advanced AF is an unusually large AF frame. (The region over which the AF system can take readings to determine focus. - Because of the larger size of the sensor in the 1Ds though, this AF area covers about 25% less of the total frame area than it did on the EOS-1D.) As with the EOS-1D and 1v, no fewer than 45 autofocus points cover a significant portion of the overall field of view. As shown in the diagram at right, seven of these are "cross" sensors, sensitive to both horizontal and vertical detail, while the remaining 38 respond to texture in the horizontal axis only. The EOS-1Ds selects the specific AF point automatically (based on the closest subject with reliable autofocus characteristics), or the user can select a specific AF point manually. The AI Servo AF system can also track moving subjects anywhere in the AF frame, if they're initially locked-in via the central AF area.
In the Manual/45-point mode, you can select any one of the 45 AF points manually, and the camera will use that point exclusively in its focus determinations. Selection is made by using both the front and back Command dials.
No two ways about it, 45 focus points are probably a lot more than you need for manual selection, and choosing just one of them could be more time-consuming than you'd like, particularly in a fast-paced shooting situation. Custom Function menu item 13-2 simplifies the AF choice, reducing the number of available AF points to 11, and arranging them in a cross pattern. Selection is again made using both the front and back Command dials.
When speed is really the issue, Custom Function menu option 13-3 further reduces the available AF points to nine, all located around the periphery of the AF frame area. The advantage of this is that only the Quick Control dial is needed to select an AF point, rotating the selection point around the edge of the AF area as it is rotated. This allows for a much faster selection, and is particularly useful for situations where the photographer is dealing with an off-center subject.
The "Assist" button on the top of the camera's rear panel offers another important speed-related feature: You can "memorize" any individual focusing point (whether at the center of the AF area, or more likely an off-center one pertinent to your particular subject), and then quickly return to it by pressing the Assist button.
Sometimes, you may want to use more than one focusing point (for example, if your subject is fast-moving, low-contrast, or if you're working in low-light conditions). For these situations, Canon provides the Focus Point Expansion option, available as Custom Function menu items 17-1 and 17-2. In these modes, you can still manually select a single focus point, but the camera then looks at up to six surrounding points to determine focus. Only the selected point lights up in the viewfinder, but as many as six other points are used to determine focus.
In addition to being able to select the AF area, you can also set the camera to One-Shot AF or AI Servo AF. One-Shot AF is intended for stationary subjects, and locks in focus on one area. In Al Servo AF mode, the camera tracks moving subjects, keeping the subject in sharp focus no matter where it appears in the frame. (As fast as 186 mph or 300 km/h, until the car is as close as 66ft/20m, when using the 300mm f/2.8L IS lens, according to Canon.)
Canon's current USM lenses allow direct manual focusing at any time, regardless of the operation of the AF system. (The mechanically-coupled manual focusing overrides any AF setting.) A few early USM lenses had "electronic manual focus", and the 1D supports manual "tweaking" of the focus setting with those lenses, if you hold down the shutter button after the initial autofocus is achieved.
A Depth of Field Preview button on the camera's front panel lets you check the depth of field and focus for the current aperture setting. The preview is displayed in the viewfinder, and is helpful for determining how much of the scene will be in focus.
Just like the Canon EOS-1D, the EOS-1Ds' AF technology is very impressive. It's both flexible and very fast, well-suited to the demands of professional sports shooters and photojournalists.
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