Canon EOS 30DBy: Shawn Barnett and Dave EtchellsMyriad minor feature and interface tweaks make a great SLR even better. <<Optics :(Previous) | (Next): Shutter Lag & Cycle Time Tests>> Page 7:Exposure & FlashReview First Posted: 04/14/2006 |
Exposure
| Free Photo Lessons | |
|
The Aperture Priority and Shutter Priority modes work much the same as on any other camera, allowing you to adjust one exposure variable while the camera selects the other for the best exposure. A Custom menu setting enables a "safety shift" option, which automatically adjusts the primary variable (aperture or shutter speed) in Av or Tv modes, if the setting you've selected won't permit a good exposure under the current lighting conditions. This could come into play if you were shooting in shutter-priority mode to achieve a motion-blur effect, but the light suddenly got brighter, pushing the required aperture value beyond what the lens could provide. In this situation, the camera would automatically boost the shutter speed the minimum amount needed to achieve a good exposure. Program mode keeps both variables under automatic control, while Manual mode gives you control over everything.
The Automatic Depth-of-Field mode (A-DEP) uses all nine autofocus zones to determine the depth of field in the active subject area. Once it has determined the range of focusing distances present across the nine zones, it automatically computes the combination of aperture and shutter speed needed to render the nearest and furthest points in sharp focus. This is a remarkably useful feature, even for professional photographers. In many situations, you want to keep several subjects in focus, while at the same time trying for the highest shutter speed (largest aperture) that will permit that. In practice, faced with such situations, I've usually resorted to just picking the smallest aperture feasible and hoping for the best. With the 30D's A-DEP mode, the camera takes the guesswork out of this process and gives you the fastest shutter speed it can manage while still keeping things in focus. (In playing with this, I was often surprised by how large an aperture in fact would work. I frequently would have chosen a much smaller aperture to stay on the safe side.)
Metering modes include the usual Center Weighted and Evaluative, but the old Partial has been replaced by a 3.5% Spot metering mode. A few photographers might upgrade for this alone.
Introduced on the 10D and continued here is an ISO speed extension, which increases the 30D's maximum ISO speed to 3,200. New to the 30D is the ability to set ISOs in 1/3 stop increments. Steps include 100, 125, 160, 200, 250, 320, 400, 500, 640, 800, 1,000, 1,250, and 1,600, plus 3,200.) For adjusting the exposure, the 30D's Exposure Compensation setting increases or decreases overall exposure from +/-2 EV in either one-half or one-third EV increments. The default step size is 1/2 EV, but you can set an increment of 1/3 EV via the camera's Custom menu. (Frankly, I've always found that one-third EV compensation is just about ideal for digicams. One-half EV steps are just too broad to set critical highlight exposures accurately.) Automatic exposure bracketing on the EOS 30D lets you set the total exposure variation (across three shots) at anywhere from +/- 1/2 or 1/3 EV all the way up to +/- 2 EV. The nice part is that the automatic variation is centered around whatever level of manual exposure compensation you have dialed in. Thus, you could set positive compensation of 0.7EV, and then have the camera give you a variation of +/- 2/3 EV around that point. Whatever EV step size is set through Custom menu also sets the bracketing step size.
I really like the amount of information the 30D gives you about its exposure, not only in terms of the settings it's using, but in the form of feedback on how pictures you've captured turned out. You can select an "Info" display mode when viewing captured images on the rear-panel LCD screen, which produces the display shown at right. Notable here is that you not only can see all the exposure parameters, but you get excellent feedback on the tonal range of the image itself. One form of feedback is the histogram display at upper right, which shows how the tonal values are distributed within the image. A new RGB histogram can be selected for this view as well. Histogram displays are useful for directly seeing how the overall exposure turned out in an image, but I've found them to be of limited usefulness for making critical judgments about highlight exposure.
Digital cameras need to be exposed more or less like slide film, in that you need to zealously protect your highlight detail. Once you've hit the limit of what the sensor can handle, the image "clips" and all detail is lost in the highlight areas. The problem is that it's quite common for critical highlights to occupy only a very small percentage of the overall image area. Because they correspond to such a small percentage of the total image pixels, the peak at 100 percent brightness can be very hard to distinguish in the histogram display. To handle such situations, the 30D blinks any pixels that are 100 percent white on its screen, alternating them between black and white. This makes localized overexposure problems leap out at you, making it very easy to control the critical highlight exposure precisely. (The sample image shown in the display above is a pathological example, chosen to show how the feature works. In practice, you'd probably never overexpose an image that badly.)
Besides the above-mentioned exposure information and feedback, the 30D's playback options include a thumbnail index display, normal full-frame viewing of captured images, and a zoomed view, as shown at right. There's also a "jump" mode, activated via the Jump button on the rear panel of the camera. Jump mode lets you very quickly move through images stored on the memory card, jumping 10 shots at a time. The EOS 30D's image playback can be zoomed in very small steps anywhere from 2-10x. Once you've zoomed in at any level, you can scroll the zoomed window all around the image area, using the large rear-panel control dial and one of the rear-panel buttons to control direction and movement.
Custom Function 17 enables a new auto zoom feature that displays a zoomed image onscreen for quick focus checks.
Another feature deserving comment is the 30D's separation of the autoexposure and autofocus lock functions. In consumer-level digicams, half-pressing the Shutter button locks exposure and focus simultaneously. You can use this to deal with an off-center subject by pointing the camera at the subject, locking exposure and focus, and then reframing the picture before finally snapping the shutter. The only problem is that you sometimes need to perform a more radical recomposition of the subject in order to determine the proper exposure. For instance, you may want to zoom in on the subject, grab an exposure setting, and then zoom back out before taking the picture. Situations like that require locking the exposure independently of the focusing, and the 30D provides for just such eventualities by way of a separate AE lock button on the back of the camera, right under your right thumb. (The "*" button.) A very handy feature indeed, for those times you need it.
If you press the AE lock while in Evaluative metering mode and use Automatic AF point selection, Auto exposure will be set based on the AF points that are chosen by the system. Likewise, if you are using Manual AF point selection, that selected point is also used for exposure.
While on the subject of what happens when you half-press the shutter button, the 30D has another new enhancement that appears on the 1D-series and 5D. You no longer need to release the shutter from the halfway position to capture another image when in One Shot drive mode. Just release partway and press the shutter again. The camera will continue to use the same exposure and focus information until you release the shutter fully.
The EOS 30D offers a full range of White Balance settings, including six presets, an Auto setting, Custom setting, and Kelvin temperature setting. The six presets include Daylight, Shade, Cloudy, Tungsten, Fluorescent, and Flash. The Custom setting bases color balance on a previous exposure, meaning you can snap an image of a gray card and base the color temperature on that image. This setting can range from 2,000 to 10,000. The Kelvin temperature setting lets you get even more specific, and offers a range of temperatures from 2,800 to 10,000 degrees Kelvin.
Color Space can be set at sRGB to Adobe RGB. The latter offers a wider gamut of colors, but your computer program needs to be properly set to take advantage of this wider range.
The EOS 30D offers a new Picture Style menu to replace the older Parameters option. The new setup makes each "Style's" settings more obvious. You can go in and change any of the settings by pressing the JUMP button, but the setting that's been changed will appear as blue rather than white text. Each of the settings--Sharpness, Contrast, Saturation, and Tone--can be set with higher resolution than was offered on the 20D. While the 20D offered a total of five settings for each item, the 30D's Picture Style offers seven for Sharpness and nine for Contrast, Saturation, and Tone. Styles include Standard, Portrait, Landscape, Neutral, Faithful, Monochrome, and User Defined 1, 2, and 3. You can either directly modify the User Defined styles, or modify an existing Style and save it to a User Defined space. In the Monochrome Style, you can choose from an array of filters and tones to modify your monochrome output. Filters include Yellow, Orange, Red, and Green. Tones include Sepia, Blue, Purple, and Green.
One of the 30D's more unique features is its two-dimensional White Balance Shift/Bracket control. Conventional white balance "tweak" adjustments are generally limited to adding blue or red, or perhaps just shifting a color temperature setting that's calibrated in units of degrees Kelvin. The problem is that controls of this sort treat color as if were a one-dimensional entity, when it's really three-dimensional in nature. I've often been frustrated when trying to adjust a camera's color balance, for instance wanting to shift it toward green, when the camera offers options of only blue or red.
On the 30D, Canon offers a two dimensional adjustment for tweaking white balance, as shown above right. The current color balance is represented by a white cursor floating in a grid representing color space. Moving the cursor up or down results in a shift toward green or magenta respectively, while moving it left or right produces a shift toward yellow or blue. Each adjustment step in the yellow/blue direction corresponds to five mireds worth of color conversion filter, and green/magenta steps are of a similar magnitude, although the green/magenta axis doesn't translate to the color-temperature shift units of mireds.
At first glance, you'd think that a two-dimensional color adjustment tool still wouldn't cover a three-dimensional color space, Canon's approach actually does just that. To understand the control, it's important to remember that color (hue and saturation, as opposed to brightness) in an RGB image is determined by the relative amounts of red, green, and blue present, not necessarily by the absolute values of each color channel. The 30D's color shift display lets you control the green channel with either positive (green) or negative (magenta) adjustments, and the blue channel with either positive (blue) or negative (yellow) adjustments. By adjusting two of the three color channels up or down, the relative amounts of all three channels can be controlled. I suspect that the actual operation on the file is more complex than we've been discussing, but one way of looking at it would be to consider the red channel to be fixed and the blue and green channels to be adjustable against the constant red level. Canon's color adjustment tool thus lets you dial in any white balance shift you'd like to make, even though it's only a two-axis control.
The Bracketing aspect of the White Balance/Bracketing control comes into play when you turn the Quick Control Dial right. This expands the single cursor dot into a horizontal row of three dots, with slightly variable spacing. These represent the successive color values that will be used for a set of three shots that bracket the white balance. You can thus set whatever basic color balance you want, and then bracket with more or less red, or more or less blue, depending on where you are in the color space. Not enough? Turning the quick dial back left switches the set of three dots from a horizontal to a vertical array, letting you bracket with more or less green/magenta, rather than red or blue.
About the only possible remaining option would be the ability to rotate the set of three dots to arbitrary angles, but I guess the Canon engineers had to stop somewhere. Regardless, the EOS 30D's white balance adjustment control goes far beyond anything we've seen on any non-Canon digital cameras, regardless of price point. (The same color control first appeared on the Canon EOS 20D and is also found on the new EOS 5D.)
Low Light Capability & Image Noise Performance
When operating the camera in full-manual exposure mode, the EOS 30D offers a Bulb exposure setting for very long exposures. Normally, exposure times are limited to a maximum of 30 seconds in Aperture- or Shutter-Priority modes, but in Manual mode, you can expose for as long as 999 seconds by selecting Bulb mode and holding down the Shutter button for as long as you want the shutter to remain open. Obviously, 999-second exposures aren't a practical reality, as sensor noise will totally swamp the signal long before that point is reached, but the 30D does seem quite able to take very long exposures with very little image noise resulting.
A full discussion of image sensor noise is beyond the scope of this review,
but the simple story is that the most obvious and objectionable noise you'll
see in long digicam exposures is so-called "fixed pattern" noise,
caused by variations in "dark current" between sensor pixels.
"Dark current" is just what it sounds like. Current (a signal)
appears even when the sensor isn't being exposed to light. When you look
at a long time exposure shot with a digital camera, you'll often see very
bright pixels, where minor manufacturing defects have resulted in unusually
high "dark current" levels. Often called "hot pixels,"
these flecks of color are very distracting visually.
The normal way to deal with hot pixels is to take an exposure with the camera's
shutter closed, immediately after shooting the subject. If this "dark
frame" is exposed for the same time as the subject was, you can largely
eliminate the hot pixel problem by subtracting the dark frame information
from the actual exposure. In practice, this works fairly well, but has the
disadvantage that you have to wait for the dark frame exposure to be taken,
requiring an appreciable amount of time in the case of long time exposures.
(If you shot a one-minute exposure for the photo itself, you'll have to
wait another minute for the dark frame exposure to be made.)
While most other high-end digicams on the market use a dark frame subtraction
method to deal with image noise, previous d-SLRs using Canon's CMOS sensor
technology apparently did something quite different, as there was very little
delay between the end of the primary exposure and the writing of the image
file to the memory card. There was clearly no "dark frame" exposure
involved. I suspect that this advanced noise reduction processing was another
consequence of the "active pixel" CMOS technology Canon developed
internally. Having active circuitry associated with each pixel in the sensor
array allows lots of fancy processing that would be impossible otherwise,
and it looks like Canon's noise reduction system takes advantage of this.
In the EOS-30D though, while apparently still using the sophisticated on-chip noise reduction processing we saw in the 10D and the conventional dark-frame subtraction we saw in the 20D, Canon has added an Auto option as well. Accessed via Custom Function 02, the "Long exposure noise reduction" seems to operate just the same as dark-frame subtraction on other cameras we've seen. The new Auto mode allows the camera to decide whether the scene and the accompanying noise needs dark frame subtraction applied. Both Auto and On do their work only on shutter speeds of 1 second or longer.
Flash
The EOS 30D's built-in flash has a guide number rating of 43 feet (13 meters) at ISO 100, translating to a range of about 15 feet at ISO 100 with an f/2.8 lens. (Reasonably powerful, but not dramatically so.) The 30D gives you a great deal of control over flash exposure, allowing you to adjust flash and ambient exposure independently of each other, in one-half or one-third EV increments. This makes it very easy to balance flash and ambient lighting for more natural-looking pictures. The 30D also uses E-TTL II control for both the built-in and compatible external flashes (according to Canon this includes the older 550EX flash, as well as the current 580EX), a new standard that promises better, more balanced exposures. Custom Function 14 turns this mode off and returns to an average metering system. E-TTL II is only available with the built-in flash or when the camera is paired with either the 550EX or the new 580EX flash.
Another nice touch is the Flash Exposure Lock button, which fires the flash
under manual control before the actual exposure, to determine the proper
exposure setting. This struck me as very handy, akin to the more conventional
autoexposure lock function for handling difficult ambient lighting conditions.
A Flash Exposure Compensation feature controls the flash exposure +/- 2
stops in 1/2 or 1/3-stop increments.
Several of the more impressive features of the Canon flash system depend on the dedicated 550EX or 580EX speedlight. Among these are true FP (focal plane) flash sync, flash exposure bracketing with external flash units, flash modeling, and E-TTL II exposure control. FP sync requires a flash unit to provide uniform light output for a relatively long period of time, long enough for the focal plane shutter curtain to fully traverse the sensor plane. On the 30D, this requires a flash duration of 1/250-second. Uniform, long-duration flash pulses like this permit use of shutter speeds as high as the 1/8,000-second maximum that the 30D is capable of. This can be invaluable when you want to exclude ambient light from the exposure. (FP sync mode is referred to as "high speed" mode on the Canon 550 and 580 flash units.)
Here's the rundown on Canon Speedlights and their compatibility with the 30D:
| Speedlight Model | On-Camera Capability | E-TTL Wireless Compatibility |
| 580EX | All | Master or Slave |
| 550EX | All | Master or Slave |
| 480EG | External auto plus manual operation | None |
| 540EZ | Manual operation only | None |
| 430EZ | Manual operation only | None |
| 420EX | All | Slave Only |
| 420EZ | Manual operation only | None |
| 380EX | All | None |
| 220EX | All | None |
| 200E | Not Compatible | None |
| 160E | Not Compatible | None |
| MR-14EX Macro Ring | All | Master Only |
| MT-24EX | All | Master Only |
| ST-E2 transmitter | E-TTL, attach to camera | Master Only |
| Non-dedicated shoe-mount units | Manual operation only | n/a |
| Studio strobe packs | Manual operation only, connect via threaded PC sync socket on camera body | n/a |
You'll note the references to "E-TTL remote"
capabilities in the table above. Canon's Speedlight system permits TTL flash
metering with multiple remote units, and even allows you to set differential
power ratios between the slaved units, over a six-stop flash exposure range.
The "Flash Modeling" feature of the 550/580EX speedlights is quite useful. With a F550/580EX connected to the 30D, pressing the camera's Depth of Field Preview button causes the speedlight to fire at 70 flashes per second for about one second. This creates the illusion of a constant light source for your eyes, letting you preview the lighting on your subject when the flash fires. VERY handy, and likely to save lots of shoot/check/reshoot time!
As alluded to above, the "X-sync" speed of the 30D is 1/250-second. (This is the maximum shutter speed that can be used on the 30D when working with a non-dedicated, FP-capable speedlight.) When used with higher-powered studio strobe systems, Canon recommends a maximum shutter speed of 1/125-second or slower, to accommodate the variable time/intensity profile of such units. Finally, via a Custom menu setting, you can program the 30D to use a shutter speed of 1/250-second in Aperture-Priority exposure mode regardless of ambient light levels. (I guess this is useful, if you know you're going to be hopping in and out of flash mode, but other than a convenient preset for the shutter speed, it's little different from simply using Manual mode to set both shutter speed and aperture simultaneously.)
Another benefit of the dedicated Canon speedlights is that they carry powerful autofocus assist illuminators that can extend the range of the built-in AF assist light of the 30D significantly. As an example, the AF assist beam on the 550EX is rated as good to about 50 feet, versus the roughly 13 feet of the lamp on the 30D itself. (Note that the ST-E2 wireless sync transmitter can also be used for AF assist during non-flash photography, a handy trick.)
 |
20D with E-TTL II |
 |
Digital Rebel without E-TTL II |
Two Continuous Shooting Modes and a Self-Timer
Among digital SLRs currently on the market, the 30D is above average in terms of shooting speed, very competitive with units it'll be stacked up against in the marketplace. The Continuous Shooting mode is rated by Canon at five frames per second, a number that matched exactly the 5.0 frames/second that I measured in my own tests. This actually exceeds the ability of most d-SLRs, which typically come in at about 3.0 frames per second, but it's nonetheless slower than the blazing 8.5 frames per second of Canon's own EOS-1D Mark II. Professional sports shooters will doubtless want more (they being a primary target of the 1D Mark II), but for most situations, I expect that the five frames per second of the 30D will be plenty fast enough. The 30D also has an unusually "deep" buffer, as it's able to capture up to 31 large/fine JPEG images or 12 RAW or 9 RAW+JPEG ones before having to pause for the memory card to catch up. The 30D also has a new 3.0 frame per second mode for those shooters who want greater buffer depth despite the loss of speed. The 30D also seems well-able to take advantage of fast memory cards, as its buffer-clear time is only 19 seconds with a Kingston 100x 2GB CF card, and only 12 seconds with a SanDisk Extreme III 1GB (Large, Fine JPEG). The maximum burst in RAW mode is 11 frames, with a 17 second time to clear with the Kingston card.
The camera's Drive setting also accesses a Self-Timer mode, which opens
the shutter 10 seconds after the Shutter button is pressed, giving you time
to dash around in front of the camera.
Reader Comments! --> Visit our discussion forum for the Canon EOS 30D!
Follow Imaging Resource: