Olympus EVOLT E-300By: Shawn Barnett and Dave Etchells8.0 megapixels, ZUIKO DIGITAL lens mount, digital SLR design, and loads of features! <<Viewfinder :(Previous) | (Next): Exposure & Flash>> Page 6:OpticsReview First Posted: 11/08/2004, Updated: 03/12/2005 |
Optics
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At the introduction of Olympus's original Four Thirds camera, the E-1, the Zuiko Digital lens system offered a variety of focal lengths, including 50mm and 300mm lengths, and two zoom lenses (14 - 54mm and 50 - 200mm). A 1.4x teleconverter was also available. Since then, Olympus has expanded their lens line considerably, to now include a 11 - 22mm f/2.8 - 3.5 wide zoom, a 40 - 150mm f/3.5 - 4.5 zoom, and a 150mm f/2.0 (!) telephoto. All of these early lenses were very much aimed at the professional market, with features, optics, build quality, and prices to match. With the introduction of the E-300 EVOLT, Olympus has also brought out a 14 - 45mm f/3.5-5.6 lens that's quite a bit more affordable.
Note that the 22.3mm diagonal dimension of the sensor translates into a 1.94x focal-length multiplier relative to 35mm cameras. For the sake of easy math though, Olympus and most reviewers (ourselves included) simply refer to it as a 2x ratio. This means that the focal lengths mentioned above should all be multiplied by two to arrive at the equivalent focal lengths in the 35mm film world. That makes the bundled 14 - 45mm lens equivalent to 28 - 90mm lens (using the literal 1.94x multiplier, it's 27.16 - 87.30mm).
Olympus has for some time insisted that the three-dimensional structure of CCD sensors demand a radically different lens design for optimum performance. Their E10 and E20 fixed-lens SLRs embodied such a design, in which additional optical elements collimated the light, insuring that light from the subject would strike the CCD surface perpendicularly across its entire surface. By contrast, with conventional lenses, light from the subject strikes the film or sensor plane at an increasingly oblique angle, as you move toward the edges of the image circle. (See the illustration above right, courtesy of Olympus.) Depending on the sensor design, this varying angle of incidence can cause problems in one of two ways. If the sensor employs microlenses to concentrate light on each pixel's active area, changes in the angle of incidence can lead to unwanted optical effects due to diffraction by the microlenses themselves. On the other hand, if no microlenses are used, collection efficiency is lower, and the decidedly three-dimensional structure of the CCD's surface can result in some of the light being shadowed from the active silicon surface by surrounding surface structures on the chip. Either case results in imperfect coupling of the light to the sensor elements.
In Olympus' "Digital Specific" lenses, an extra group of optical elements collimates the light (makes all the rays parallel), so it impinges on the CCD at right angles to its surface all across the frame.
Actually, Olympus has done a number of things in the design of their lenses for the Four Thirds system to improve image quality. To call attention to the extent of these design improvements, they've branded them as "Zuiko Digital (tm)" lenses. (I'm told that Zuiko means "Light of the Gods," presumably in Japanese.) In addition to the special "digital specific" design described above, Zuiko Digital lenses also incorporate improvements in lens molding and polishing accuracy, multi-coating, centering of the lens elements within the mounting system, increased use of ED glass and aspheric elements, and dual-sided aspheric elements, the latter of which Olympus claims as an industry exclusive. The actual impact of these enhancements remains to be seen (if/as/whenever I manage to find time to test both Zuiko and third-party optics on an EVOLT or other Four Thirds camera), but the promise is that Zuiko Digital lenses will have better resolution, color rendering, and flare characteristics than even the best conventional designs. The 14-45mm "kit" lens that's bundled with the EVOLT shows moderate barrel distortion at the wide angle end of its range, but has surprisingly little chromatic aberration and excellent corner sharpness for an inexpensive optic.
Another area in which the Olympus E-300 EVOLTs capabilities exceed the general run of d-SLRs out there has to do with the in-camera lens-correction processing that it's inherited from the E-1. One of the biggest innovations embodied in the Zuiko Digital lenses is that they also support a greater degree of communication between lens and camera than has heretofore been the case, with some interesting consequences. Olympus claims that part of this increased communication will benefit autofocus speed and exposure determination, although they haven't said how this might work. It does appear though, that Zuiko Digital lenses pass information about their optical characteristics to the camera body, including information on geometric distortion. In the pro-oriented E-1 SLR, this information can be used to correct light falloff in the corners of the frame, via a menu option called "Shading Compensation." (For those of you unfamiliar with the term "shading," this phenomena is almost universally, if erroneously, referred to as "vignetting.") Based on a conversation with Olympus, the E-300 apparently always performs this correction in-camera, rather than providing it via a menu option. Perhaps more interesting though, is that the data about geometric distortion that's captured by the camera body is written into its RAW files, so the Olympus Master software can correct for such lens defects after the fact, back on a host computer. The result can be very low distortion with relatively inexpensive lenses. (To the best of our knowledge though, only the Olympus Zuiko Digital lenses offer this capability: Third-party Four Thirds format lenses do not.)
The Olympus E-300 employs a three-point TTL Phase Difference Detection autofocus system, and the three AF points are outlined in black in the viewfinder display. Pressing the AF Area Selection button on the rear panel lets you manually select which of the AF points you'd like to base focus on, or set the AF area to automatic selection (all three AF points active). The AF button on the rear panel lets you select Manual, Single AF, or Continuous AF modes. There's also an option for Single AF + Manual Focus. When manual focus is enabled, you simply turn the focus ring around the outside of the lens to set focus. The focus indicator in the optical viewfinder (a solid green circle) lights to indicate that you've achieved accurate focus. Note that this is not a true mechanical or analog focus, however. Turning the ring simply activates the camera's focus mechanism, actuating the focus motor built into the lens. Single AF mode means that the camera only sets the autofocus when the Shutter button is halfway pressed, while Continuous AF mode continuously adjusts the focus without you having to halfway hold down the shutter release (good for moving subjects). Continuous AF uses what Olympus calls Predictive AF technology, in that the camera anticipates where the subject will move to next and adjusts focus just before it reaches that point. As far as we could tell from the operation of the prototype sample we received for this review though, the Predictive AF doesn't involve following an active subject from one AF region to another, but rather simply predicts whether a subject under a single AF point is approaching or receding The mode combining Single AF and Manual focus tells the camera to set focus with a half press of the Shutter button, but leaves the manual focus ring active so that you can fine tune the setting before pressing the shutter button the rest of the way to trip the shutter..
The Olympus E-300 also lets you tell it whether to adhere to focus- or release-priority. In focus-priority mode, the shutter won't fire unless the subject is properly focused. Conversely, release-priority means that the shutter will fire whenever you tell it to, whether the subject is focused or not. In a nice touch, the E-300 lets you determine select focus or release priority independently for single-shot and continuous shooting modes. (I can imagine myself wanting to insist on focus priority for single shots, but preferring release priority for continuous shooting, to let the camera just take its best shot at tracking a moving subject, perhaps settling for slightly misfocused images, rather than missing the shot entirely.)
Though aperture settings will differ depending on the lens in use, the EVOLT does feature a Depth of Field Preview button that stops down the lens to the set aperture when pressed. Common on most high-end SLRs, this lets you focus with the lens wide open for a bright viewfinder image, and then preview depth of field by momentarily stopping down to the shooting aperture.
An AF illuminator option can be turned on through the camera's Record menu, to help the camera's AF system determine focus in dark shooting conditions. The camera actually uses light from the flash as the AF illuminator, so the flash must be upright and enabled for this option to be available. Though our prototype unit couldn't, the final version of the Olympus EVOLT will fire the flash for AF assist even while the flash itself is off; that is, it must still be deployed, but you can still take a long exposure sans flash.
Third-Party Four Thirds-System Lenses
One of the drawbacks to the original E-1 system was the high cost of the Olympus Zuiko Digital-Specific lenses. While of very high quality and not dramatically higher-priced than pro-grade lenses from manufacturers like Nikon and Canon, their cost could put the whole E-1 system out of reach for even well-heeled amateur photographers. (Or pros with limited budgets, for that matter.) For quite a while after the E-1's announcement and retail availability, there was no option in the marketplace for E-1 lenses other than Olympus' own offerings. Olympus is now moving to correct this issue, with the announcement of their own 14-45mm optic that I mentioned above. In Spring of 2004 though, Sigma announced Four Thirds-compatible lenses at CeBit. Sigma's announcement covered three lenses, an 18-50mm f/3.5-5.6 zoom, a 55-200mm f/4-5.6 zoom, and an 18-125mm(!) f/3.5-5.6 zoom. As of this writing (early Spring, 2005), Sigma has announced additional "DC" lenses, including a 10-20mm ultrawide zoom lens, an 18-50mm f/2.8, an 18-200mm f/3.5-6.3 zoom, and a 30mm f/1.4 fixed focal length model. (This last is particularly interesting. The 30mm focal length corresponds to 50mm focal length considered "normal" for 35mm film cameras when it's used on most d-SLRs, or a 60mm equivalent on the Olympus E-300. What's significant is that this is the first significantly new optical formulation for a "normal" lens to hit the market in many years, taking advantage of modern lens design and technology. Sigma is well-known for producing optically sharp lenses at very attractive prices, and these Four Thirds models appear to be no exception. With an independent lens manufacturer now making lenses, the Four Thirds system has taken a big step forward toward being a true multi-vendor standard. (All that's missing now is for another manufacturer to produce a Four Thirds camera body.)
"Supersonic Wave Filter (tm)" Automatic Sensor Cleaning
Here's a feature that made me sit up and take notice: Built-in ultrasonic sensor cleaning! This was first introduced on the E-1 SLR, and has been carried forward to the E-300, despite the latter's greatly reduced cost. This is a feature that's hard to evaluate in any sort of a rigorous, quantitative way, but that appears to work quite well, based on subjective observation.
Dust has proven to be a bane for digital SLR users from the beginning. In film cameras, the imaging surface (the film) is constantly refreshed as each new frame is advanced. Any dust that might accumulate on one frame will thus not affect subsequent ones. In digital SLRs though, the sensor surface is fixed, so any dust falling on it tends to stay there, the surface becoming increasingly dirty over time. Various accessories are available to clean CCD surfaces, but their use presents an ongoing risk of accident. (That is, while the cleaning gadgets themselves may be perfectly safe, every time you open your SLR and start sticking things inside the camera body, there's a finite risk that you'll do something stupid and damage the sensor chip.)
In the E-1 and now the EVOLT, every time the camera is turned on (or commanded to do so via a separate menu setting), an ultrasonic system activates, vibrating the protective cover glass over the sensor at a frequency of 350,000 cycles/second, thereby dislodging any dust particles that may have settled on the sensor's surface. (Dislodged dust is collected and trapped in an internal receptacle, so it won't float around the mirror compartment to cause more problems down the line.) A full cleaning cycle takes only 200 milliseconds. (0.2 seconds) As noted, I don't have any way to objectively measure the effectiveness of this system, but can say that I've seen virtually no evidence of dust on the sensor throughout my testing and use of both the original E-1 and now the new EVOLT.
To set appropriate expectations for Olympus' Supersonic Wave Filter system,
it's important to note that it almost certainly won't be effective against grease smudges caused by fingerprints. - So continue to be careful about putting your fingers inside the mirror compartment when the sensor is exposed.
Image Sensor
The sensor chip used in the EVOLT calls for special comment as well, although the test results I obtained from a production-level E-1 model (which uses the same basic sensor technology) lead me to wonder slightly whether the special attention is in fact deserved. Its claims to fame should be lower noise
and increased dynamic range, but there are a lot of system-level factors that
can affect noise levels and dynamic range, regardless of sensor characteristics.
The Four Thirds initiative is a joint effort by three companies: Olympus, Kodak, and Fuji. We haven't heard anything about Fuji's possible plans yet, but Kodak was clearly a major partner of Olympus in the E-1 and now in the EVOLT, as it's their sensors that are used in both cameras. Kodak was a dominant player in the early digital SLR market, thanks largely to their advanced sensor technology. Now, with the advent of Four Thirds and their participation in the E-1 and EVOLT with Olympus, they appear poised to regain significant market share for their chips. While Kodak has recently struggled in the SLR marketplace, their CCD sensor technology has historically been second to none: Kodak's specs for quantum efficiency, electron capacity, and thermal noise levels are thoroughly state of the art. They also have a very well-developed design base and semiconductor manufacturing process for creating "full-frame" CCDs, which have considerable inherent advantages over the more common interline-transfer designs used in most digital cameras currently on the market.
While considerably more difficult to manufacture than interline sensors, the full-frame design potentially provides better light sensitivity and a significantly improved signal to noise ratio. This is because almost 100% of the silicon's surface area is available for light collection, since the charge transfer off-chip occurs in the sensing elements themselves. By contrast, in an interline-transfer CCD design, the charge-transfer registers are located alongside the photodiodes, consuming considerable silicon real estate. This also means that frame-tranfer CCDs have less need for the "microlenses" commonly used with interline-transfer chips to improve light collection efficiency, although it turns out that the sensor on the Olympus E-300 still uses them to concentrate light on the area of each pixel with the best light sensitivity.
The electronic structure of full-frame CCDs also results in a much higher "saturation voltage" than that of equivalent interline-transfer designs. Combined with the low thermal noise that characterizes Kodak's chips, the overall result is that the CCDs used in the E-1 and EVOLT should have nearly twice the dynamic range of competing interline-transfer units, with the same pixel dimensions. (Dynamic range is the range of light to dark values that can accurately be recorded.) Note though, the emphasis placed on the issue of pixel dimensions in the previous statement. The combination of smaller overall sensor dimensions (which result in the 2.0x focal length multiplier, vs the 1.5-1.6x that's more common in competing d-SLR models) and 8 megapixel resolution means that the pixels in the EVOLT's CCD chip are rather small, with a 5.4 micron pitch.
In our testing of the Olympus E-300 EVOLT, we found that its image noise levels were higher than those of competing d-SLRs having the larger APS-sized sensors, but not dramatically so. (Image noise at ISO 1600 was markedly higher, but that also appears to be at least partly due to the rather conservative anti-noise processing that Olympus uses, the engineers apparently having chosen to preserve more subject detail at high ISO, at the cost of somewhat higher noise. - A choice that I personally prefer.) It's not clear whether it's a consequence of the frame-transfer design or not, but the image noise in high-ISO images from the EVOLT has a rather fine "grain structure," which makes it less objectionable than it might be otherwise.
The net of all this is that Kodak's frame transfer technology seems to just about make up for the smaller pixel dimensions that result from the smaller sensor dimensions of the Four Thirds standard, and higher pixel count used in the E-300. I'd like to see somewhat lower overall noise at ISO 1600, but would probably find the noise levels I did encounter there acceptable for situations where the resulting images would be printed at smaller sizes. (Say, 5x7 or below.)
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