Canon EOS 20D, ISO 100 (Photo by Rob Galbraith/Little Guy Media)
Image Sensor and Image Processing
Canon's decision several years ago to throw their sensor-development resources into CMOS sure seems to be paying dividends now. With each new Canon digital SLR model we've seen better overall image quality than the last, and the EOS 20D is shaping up to be no exception.
At the heart of the EOS 20D is a Canon-developed CMOS image sensor. Its physical dimensions roughly mirror those of the 10D's CMOS sensor, at 22.5mm x 15mm, which means it has about the same 1.6x field of view magnification factor as the 10D too. The total number of pixels has increased, however, to about 8.5 million pixels. The number of actual image pixels in EOS 20D photos, with the camera on its highest resolution JPEG or RAW CR2 setting, is about 8.2 million. In fact, the 20D's image dimensions are identical to files from the EOS-1D Mark II, despite having a physically-smaller image sensor.
As the pixel count goes up, the ever-present threat of increased noise visibility goes up as well. With a pixel pitch of 6.4µm square, the EOS 20D has the smallest pixels of any Canon digital SLR produced to date. Which also means Canon faced the biggest challenge to date keeping sensor noise at bay. To tackle this potential problem, Canon has ported some of the design improvements first seen in the EOS-1D Mark II's image sensor, and added a few additional CMOS twists as well:
- The same higher-efficiency microlens design as used in the EOS-1D Mark II's sensor is present in the 20D's sensor. Improving a sensor's light gathering ability is a key way to reign in noise, since it efectively increases the signal-to-noise ratio.
- A new 3-stage, on-chip noise reduction circuit was developed (the EOS 10D and EOS-1D Mark II, by comparison, employ single-stage on-chip noise reduction). According to technical documentation from Canon, this circuit "cuts the creation of desirable artifacts by amplifying the sensor's output signal in slow-read steps."
The sum of these changes is promised lower noise, without smearing image detail, throughout the camera's ISO 100-3200 range (C. Fn 8-1 must be set for ISO 3200 to be selectable), but especially at ISO 400 and above.
In fact, Canon literature promises that ISO 1600 photos taken with the EOS 20D will appear to have about the same noise levels as ISO 400 photos taken with the EOS 10D (which produces reasonably clean ISO 400 files). This is a heady claim, one that we look forward to evaluating.
We can say, after shooting a soccer match at ISO 3200 with a preproduction EOS 20D in available darkness, that this camera's upper ISO range is really impressive. In fact, quickly comparing side-by-side frames at ISO 3200 from an EOS-1D Mark II and EOS 20D, the 20D's noise levels appear to be slightly lower. But this assessment should be considered preliminary at best.
Canon is also promising reduced fixed-pattern noise in long exposures photos, relative to the EOS 10D. The reasons for this are two-fold:
- The EOS 20D's sensor design, says Canon, is simply less noisy.
- A long exposure noise reduction mode, that uses the noise-zapping dark frame subtraction technique, has been added to the 20D (in addition to the same real-time long exposure noise processing found in the 10D). It can be switched on or off; when on, it kicks in when the exposure time is 1 second or longer. Unlike the EOS-1D Mark II and EOS-1Ds, however, the long exposure noise reduction mode of the EOS 20D locks up the camera after each exposure for an amount of time equivalent to the exposure. We love using the EOS-1D Mark II or EOS-1Ds for fireworks, because even with their dark frame subtraction-based long exposure noise reduction enabled, these cameras juggle the shooting and dark-frame subtraction processing in a manner that allows the next frame to be shot almost immediately after the shutter closes in many cases. This bit of digital alchemy is, to our knowledge, unique to these models. It would have been great to see this capability extended to the EOS 20D. Though, it should be noted that the 20D's multi-second exposures so far look impressively clean even with long exposure noise reduction switched off; the real-time noise processing applied during long exposures, even without the additional aid of dark-frame subtraction, is as or more effective as the real-time noise processing in the 10D (which lacks the additional dark frame subtraction mode).
In addition to the increased resolution and promised reduced noise, the DIGIC II processing chip is said to bring about "improved color reproduction of high-saturation, bright subjects, improved auto white balance precision, and wider dynamic range in highlight areas."
Other image sensor and image processing items of interest include:
The Large (3504 x 2336 pixels), Medium (2544 x 1696 pixels) and Small (1728 x 1152 pixels) resolution settings on the EOS 20D are identical to the Large, Medium2 and Small resolutions settings on the EOS-1D Mark II. The EOS-1D Mark II, however, has an additional resolution setting, Medium1, which is 3104 x 2072 pixels.
The EOS 20D is the second Canon digital SLR to offer the selection of colour space separate from the colour look. This is the way all cameras should work, so it's great to see that Canon appears to be standardizing on this approach. Two colour spaces are selectable: sRGB or Adobe RGB.
One of the characteristics of Nikon's digital SLR lineup that we appreciate is the fact that, across both professional and midrange cameras, the bulk of the image processing settings, file format options (including the NEF RAW file format) and image review functions are the same, in addition to a fair bit of commonality in basic camera operation. As a result, it has been possible to use a D1X and D100, or D2H and D70, mostly interchangeably at certain assignments, because the overall similarities in the camera models outweigh the differences. Including similarities in the overall colour look of the pictures each generates (though the D2H goes its own way in a few areas).
Not that long ago, the experience in the Canon world was quite different. For example, an EOS-1D and EOS 10D have different RAW file formats, different image processing controls and they most definitely don't share the same overall colour look. While the differences are hardly insurmountable, they never made much sense. Apparently the lack of commonality didn't make much sense to Canon either: with the EOS 20D and EOS-1D Mark II, Canon appears to be signaling their intent to adopt a more-unified approach, and that can only be better for the photographer using a collection of Canon digital SLR cameras in different price ranges. The execution isn't yet perfect, but there is more overlap in image processing controls in particular, and greater consistency in image appearance (including the identical resolution, in the case of the 20D and EOS-1D Mark II) across disparate Canon models.
And, finally, the CRW RAW format and its twin files for each photo taken has gone the way of the dodo. In its place in the EOS 20D is the same RAW CR2 format introduced in the EOS-1D Mark II. But the 20D, like the 10D before it, still insists on creating a new folder every 100 photos, and the file name prefix is still IMG (or _MG if the colour space is set to Adobe RGB) and not something unique to the camera or user-selectable. So, Canon has some distance to go yet in fully-unifying its high-dollar and lower-dollar digital SLR's.
New to the EOS 20D, and not found in a 1-series digital SLR, is a black and white mode. Back when the Nikon D1 was current, we used its black and white mode from time to time, though we usually opted to shoot colour, then remove the colour in Photoshop using the technique best-suited to the particular tones in the frame. And while that will probably still be the preferred method with 20D photos for black and white afficionados, Canon has provided an interesting range of conversion options built into the camera, including ones that simulate the use of coloured optical filters on the lens. Contrast and Sharpness are also adjustable, in 5 increments, and it's possible to apply toning effects too. The menu grabs below show the range of effects options.
White Balance Correction With the EOS-1D Mark II, Canon introduced White Balance Correction, a function that allows the photographer to warm or cool the look from a given white balance setting, as well as correct for a green or magenta cast caused by some artificial light sources. The method for setting White Balance Correction in the EOS-1D Mark II is usable, but not as intuitive as we'd like. Plus, it would be great if the user could store White Balance Corrections as part of the user-definable Color Matrix sets in that camera, to create a single setting for Mercury Vapor-lit basketball, for example.
In the EOS 20D, Canon has addressed our first concern: making the function more intuitive to set. A new menu item, WB SHIFT/BKT, provides a grid interface for the setting of both White Balance Correction and White Balance Bracketing, and the new multi-controller makes short work of moving about the grid to dial in the amount of White Balance Correction desired (the Quick Control Dial handles White Balance Bracketing). The grid is more than just a convenient way to implement this feature. It accurately conveys the dual-axis relationship between the amber-blue and green-magenta corrections offered. One odd omission: pressing the centre of the multi-controller doesn't move the indicator back to the centre of the grid.
White Balance Correction, White Balance Bracketing
This is definitely a smarter way to implement White Balance Correction, and not only because you get to utter the phrase "you sunk my battleship" several times during its setup. With White Balance Correction dialed in, a small WB icon appears on the top LCD and in the viewfinder information. This is all good. We would have preferred it if Canon had gone one step further and also made White Balance Correction one of the Parameter Set options.
White Balance Correction is gradated in 18 steps along each of the amber-blue and green-magenta axes. Along the amber-blue axis, 3 steps of correction is equal to a 5 mired change. It's possible to combine White Balance Correction with White Balance Bracketing.
In-camera sharpening As with the EOS 10D, it's not possible to disable the sharpening of in-camera JPEGs; the 5-increment Sharpening parameter runs from Low to High. Based on our initial look at in-camera sharpening, however, it seems to work okay for its intended purpose: that is, compensating for the softening effect of the low-pass optical filter in front of the sensor.
Custom White Balance Using the Custom White Balance (WB) function of a modern Canon digital SLR is a two-step operation. First, take a picture of a neutral object, then set a Custom WB from that frame. Second, remember to change the WB setting to Custom. The 20D doesn't automatically change WB to Custom after the user stores a Custom WB, which we would like to have at least as an option, but it does now display a reminder on the rear LCD (as shown below) if the WB setting is something other than Custom currently. A similar reminder appears when dialing in a colour temperature.
The camera doesn't intervene to prevent the setting of a Custom WB from a completely overexposed frame. The result, the few times we've tried it thus far, is a heavyish green cast across subsequent frames shot on Custom WB. The EOS-1D Mark II displays an "Unselectable Image" message in this situation, so it's surprising to not see the same warning appear on the 20D's rear LCD.
E-TTL II and the EOS 20D
Despite taking its TTL flash exposure measurement from a broader area of the scene than most or all previous Canon cameras that utilize E-TTL, the EOS 10D's flash exposures, with a flash like the Speedlite 550EX, are still inconsistent, and sometimes frustratingly so. Fortunately, the 20D has shed E-TTL altogether. The new TTL flash control algorithm introduced in the EOS-1D Mark II, called E-TTL II, has been employed in the EOS 20D now too.
E-TTL II uncouples the Evaluative flash exposure calculation from the active focus point, and instead compares the readings of both ambient light and a pre-flash from an EX-series Speedlite across all 35 of the 20D's metering zones.
This comparison enables the system to determine where in the scene the flash exposure should be targeted, as well as which areas in the scene are likely to be reflections or other specular highlights that should be ignored. Focus distance with newer Canon EF lenses also forms part of the calculation, though only as a sanity check on the ambient/flash difference information gleaned from the pre-flash just before the photo is taken.
This approach, in theory (and in practice based on our experience with the EOS-1D Mark II), enables more consistent and reliable TTL flash exposures than has previously been possible with E-TTL, even when focusing and recomposing (which was previously a Canon Speedlite no-no).
External Speedlites whose names end in EX, including the 550EX and new 580EX, and the built-in flash, are controlled by E-TTL II. Older, non-EX Speedlites will not function in TTL or A-TTL on the 20D. The standard top flash sync speed is 1/250. With High Speed Sync enabled on EX-series Speedlites that offer this capability, the flash sync range is extended to 1/8000. The trigger voltage limit of the PC sync port is 250V.
As with the EOS-1D Mark II, it's possible to disable Evaluative analysis of the flash output, and instead switch to an averaging-type flash metering across the camera's 35 metering zones. This can be accomplished one of two ways:
- By using rear-button focusing. When the 20D is configured to engage the autofocus using the rear AE Lock (*) button (by setting C. Fn 4-3, for example), the camera will switch from Evaluative E-TTL II to Average flash metering depending on whether the AE Lock Button is pressed down or not. With it pressed, you get Evaluative; with it released, you get Average. This is the same as the EOS-1D Mark II. With that camera, we would prefer the option of making E-TTL II be the flash metering method of choice regardless of whether the AF system is engaged, since for almost every situation we've compared E-TTL II's Evaluative to Average flash metering with the EOS-1D Mark II, E-TTL II has been closer to the mark. We're assuming, then, that the same nothing-but-E-TTL II option in the 20D would also be welcome for rear-button focusers.
- By changing C. Fn 14 to 14-1 (Average). Set this way, the EOS 20D will always average the flash exposure, regardless of focus mode.
Given the EOS-1D Mark II and 20D use the same E-TTL II algorithm, it's reasonable to expect similar, consistent flash performance. The former camera has a 21-zone meter, the latter a 35-zone meter, so it's probably reasonable to expect some differences, too. E-TTL II has brought truly workable TTL flash to the EOS-1D Mark II, so overall we're optimistic about E-TTL II in the 20D also.
Flash Exposure Lock (FEL) junkies (which includes us with Canon models prior to the EOS-1D Mark II) should note that the 20D doesn't have a dedicated FEL button, like 1-series digital SLR's do. While FEL can be set using the AE Lock (*) button, this is only possible when the camera is not configured for rear-button focusing. This is the same as the 10D. With that camera, however, C. Fn 13 can be set to 13-4, thereby turning the Assist button into the FEL set button. When the Assist button disappeared from the 20D, so too did this functionality. While the new multi-controller's function can be changed through a Custom Function, FEL is not one of the available options.
While we haven't used FEL nearly as much since the EOS-1D Mark II's inception, it still seems short-sighted to not provide a way for the rear-button focus crowd to set an FEL from time to time, without having to resort to front-button focusing temporarily.
And finally: when the built-in flash is used, or the external flash is the Speedlite 580EX, and the white balance setting is AWB or Flash, colour information from the flash is woven into the white balance calculation. A firmware update for the EOS-1D Mark II is expected to bring this same feature to that camera when the 580EX is used.
At a glance, the EOS 20D looks an awful lot like the EOS 10D. The new camera is a bit smaller and lighter, the shape of the prism and built-in flash is different, a few of the 10D's back buttons are gone in favour of the new multi-controller, the top dial is slightly larger, the mirror box is smaller and of course the name badge on the front says 20D. The overall effect, holding the camera, is much the same as holding the 10D. Which is good - the 10D is a tight, small SLR body that feels good in the hand.
There are a few differences in the body that are worth pointing out, almost all of which improve upon the 10D:
Viewfinder Canon's 1-series digital SLR cameras have sharp, clear, colour-cast free viewfinders. They're wonderful. By comparison, the 10D's viewfinder image is somewhat flat and a bit fuzzy to look through, especially if one's eye isn't carefully aligned with the centre of the eyepiece. This is typical of most cameras in the 10D's class in our experience, and it makes it more difficult to see the focus snap in when manual focusing. The 20D viewfinder and its New Precision Matte Screen add up to a clearer, sharper image that's closer in quality to 1-series digital SLRs than the 10D, though the size of the viewfinder image is still about the same as the 10D.
There is one quirk worth noting: when looking through lenses whose maximum aperture is slower than about f/4, a faint graininess appears across the viewing area. With an f/5.6 lens attached, the effect is fairly obvious. The 10D, by comparison, doesn't exhibit a similar graininess with slower aperture lenses. The graininess, while odd, isn't enough to make us prefer the 10D's viewfinder by any means, and the effect is completely absent from the 20D's viewfinder with f/2.8 glass. But the effect is odd nonetheless.
The viewfinder information beneath the photo is nearly identical to that of the 10D, though a new WB indicator has been added to show when White Balance Correction is set to something other than its default.
Not changed is the single-digit display of frames remaining. With a maximum 9 frame RAW or JPEG buffer, a single digit did the job in the 10D nicely. With the 20D set to JPEG, however, the buffer limit always starts out at more than 9 frames, which means that the frames remaining display stays frozen at 9 unless an extended sequence has been shot or the CompactFlash card is nearly filled and there's only room for 8 or fewer additional frames. When the 20D is set to RAW or RAW+JPEG, the frames remaining counter is more useful, since the buffer limit is 6. To better serve JPEG shooters, however, a 2-digit frames remaining display would be preferable.
Rear control layout The 20D has shed the Assist and Direction Switching buttons of the 10D, and gained a 9-way multi-controller. The multi-controller is used to pan about zoomed photos (replacing the function of the Direction Switching button), change AF points, set White Balance Correction and White Balance Bracketing, return AF detection to the centre point (replacing the function of the Assist button) and to adjust the amount of trim when printing directly from the camera.
At first glance, the multi-controller (shown at right) looked to us like it shouldn't work all that well, since it's just so small. In practice it's a snap to operate, even with light gloves on, though targeting the 45-degree positions of the multi-controller requires a little finesse.
To make way for the multi-controller, the on/off switch for the Quick Control Dial (QCD) has become part of the power switch for the camera. Now, the power switch has three positions: OFF, ON (QCD disabled) and ON (QCD enabled).
To protect (tag) a photo requires diving into the menu system and selecting the photo. We would have preferred the Direction Switching button be converted to a Protect button, instead of being dispensed with altogether.
Image review screen It's the same 1.8", 118,000-dot TFT LCD as found in the EOS 10D. It's vastly more usable, however. The 10D's review screen is too light and bright, even with the brightness turned all the way down. And colour accuracy is only so-so, even by rear LCD monitor standards.
By comparison, at the default brightness setting (the middle of a 5-increment control), overall image brightness and image colour is a reasonable match for a calibrated computer monitor. Reasonable, that is, for a 1.8" LCD. Canon appears to have done a good job of tuning the LCD's circuitry to get the most out of its 118,000 pixels. The revamped image brightness in particular is a welcome change, and makes it easier to determine whether the exposure is in the ballpark by glancing at the image on the LCD alone (though the histogram and overexposed highlights indicator of the info screen remain a critical part of any exposure assessment).
Also improved is the clarity of the zoomed version of an image (shown below). With the 10D, Digital Rebel/300D and EOS-1D Mark II, even small group photos can look fairly fuzzy when zoomed much beyond the halfway point of the 10X zoom range. With these cameras, it hobbles the usefulness of the zoom for checking critical focus. The enlarged image of the 20D stays sharper and clearer deeper into the zoom range, though at 10X there is still some fuzzifying going on. We'd like to check this with more pictures than what we've shot in the past few days, but so far we're optimistic that the 20D's image review screen is going to be a trustworthy image assessment tool.
It's also quicker to use. As we noted earlier, the 20D is the first digital SLR from Canon to allow photos to be reviewed, selected and enlarged as the camera is still writing those photos to the CompactFlash card. This feature isn't implemented quite as seamlessly as it is in Nikon cameras, but it's close. The menu system can also be accessed and options changed while the camera is mid-write.