Canon EOS-5DBy: Dave EtchellsSlightly smaller and lighter upgrade brings greater speed and ease of use along with higher res and lower image noise. <<Optics :(Previous) | (Next): Shutter Lag & Cycle Time Tests>> Page 6:Exposure & FlashReview First Posted: 04/02/2006 |
Exposure
Like the rest of the EOS line of digital SLRs, the 5D provides as little or as much exposure control as you could want. Standard exposure modes include the usual Program AE (shiftable), Aperture-Priority, Shutter-Priority, and full Manual modes, as well as Bulb and Custom modes. The full Auto mode takes over all camera functions, turning the 5D into a very simple point and shoot camera, albeit a very capable one. 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, though you can "shift" the exposure bias toward faster or slower shutter speeds or larger or smaller lens apertures by turning the Main dial. As you'd expect, Manual mode gives you control over both aperture and shutter speed simultaneously. The Bulb exposure mode continues the full manual exposure control, but allows the shutter to remain open as long as 999 seconds. Finally, Custom mode simply accesses a set of presaved camera settings, saved through the Register Camera Settings option of the record menu.
While the 5D doesn't offer the traditional preset Scene modes seen so frequently on other digital cameras, it does feature a Picture Style menu option, that accesses a series of preset shooting parameters. You can choose between Standard, Portrait, Landscape, Neutral, Faithful, and Monochrome modes, or save up to three sets of custom settings (with predetermined sharpness, contrast, color saturation, and color tone settings). Most of these are pretty self-explanatory, but the Faithful option deserves some further explanation. In Faithful mode, the camera automatically corrects color on subjects photographed under a color temperature of 5,200K. (A slightly warmer color balance than that of "standard" daylight.) In this mode then, the color balance will be referenced (more or less) to daylight, preserving the color cast of the scene illumination. (Very handy for preserving light color in shots captured at dawn or sunset, or under colored artificial lighting.) Under the Monochrome option you have access to sharpness and contrast adjustments, but Filter and Toning effect options are added. In this mode, Filter Effects offers yellow, orange, red, and green enhancements, similar to putting a colored filter over a lens when shooting black and white film. The Toning Effect lets you tone an image sepia, blue, purple, or green.
Commonplace on Canon's high-end EOS SLRs is an ISO expansion option, which increases the 5D's maximum ISO speed to 3,200 and drops the minimum speed to 50. Alternatively, you can adjust the ISO from 100 to 1,600 in one-third-stop increments, or select an Auto setting. For adjusting the exposure, the 5D'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 digital cameras. One-half EV steps are just too broad to set critical highlight exposures accurately.) Automatic exposure bracketing on the EOS 5D 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 5D 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. In capture mode, pressing the "Info" button shows the very detailed display shown at right, listing the current status of essentially all the image-related settings.
In Playback mode, 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. 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 5D 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 right is a pathological example, chosen to show how the feature works. In practice, you'd probably never overexpose an image that badly.)
A particularly nice feature of the Canon 5D's histogram display is the option to show separate red, green, and blue histograms, as shown at right. This can give you further insight into what's going on with an image's exposure, and is particularly helpful with strongly colored subjects, where you may be able to see saturation of an individual color channel that might not be discernible in the brightness-only histogram. The separate RGB curves can also help in judging overall color balance.
Besides the above-mentioned exposure information and feedback, the 5D'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 5D'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 rear-panel multi-controller joystick.
Another feature deserving comment is the Canon 5D's separation of the autoexposure and autofocus lock functions. In consumer-level digital cameras, 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 5D 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.
The EOS 5D 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. The Kelvin temperature setting lets you get even more specific, and offers a range of temperatures from 2,800 to 10,000 degrees Kelvin.
One of the 5D'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 5D, 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 5D'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.
"But wait, there's more!" (To steal a line from TV infomercials.) 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 5D'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-30D.)
Low Light Capability & Image Noise Performance
The EOS 5D offers a Bulb exposure setting for very long exposures (B on the Mode dial). 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 5D 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 digital camera 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 digital cameras 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-5D though, while apparently still using the sophisticated on-chip noise reduction processing we first saw in the 10D, Canon has also included an option for conventional dark-frame subtraction 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 it on. The difference with the 5D though, is that there's precious little image noise to be subtracted out, at least at exposure times of 30 seconds or less, where I did essentially all my low-light shooting. I can imagine the dark-frame subtraction option being useful for astronomers doing 5-minute exposures with the 5D, but it will add little to most users' image quality. (I did try a pair of 10-minute exposures with the 5D, one with long-exposure noise reduction turned on, the other with it off, and there was definitely a noticeable improvement with it enabled. It's sure a long time to wait for the camera to come back to you though, when you're waiting for a 10-minute dark-frame exposure to complete!)
Flash
The EOS 5D does not offer a built-in flash, but instead features a top-mounted hot-shoe and a PC sync terminal. The 5D uses E-TTL II control for compatible external flashes (according to Canon this includes the earlier 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.
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 "film" plane. On the 5D, this requires a flash duration of 1/200-second. Uniform, long-duration flash pulses like this permit use of shutter speeds as high as the 1/8,000-second maximum that the 5D 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 5D:
| 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 5D, pressing the camera's Depth of Field Preview button causes the speedlight to fire at 70 flashes per second for about a 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 5D is 1/200-second. (This is the maximum shutter speed that can be used on the 5D 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.
Another benefit of the dedicated Canon speedlights is that they carry powerful autofocus assist illuminators. As an example, the AF assist beam on the 550EX is rated as good to about 50 feet. (Note that the ST-E2 wireless sync transmitter can also be used for AF assist during non-flash photography, a handy trick.)
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20D with E-TTL II |
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Digital Rebel without E-TTL II |
Continuous Shooting Mode and Self-Timer
The 5D's Continuous Shooting mode is rated by Canon at about three frames per second, for a maximum of 60 large/fine files or 17 RAW ones. As usual though, note that actual frame rates and the maximum number of images in the series will depend on shutter speed, file size, and the amount of space available on the memory 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.
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