Olympus EVOLT E-500By: Shawn Barnett and Dave Etchells8.0 megapixels, ZUIKO DIGITAL lens mount, digital SLR design, and loads of features! <<Optics :(Previous) | (Next): Exposure & Flash>> Page 7:Lens TestsReview First Posted: 09/25/2005, Updated: 12/05/2005 |
Lens Tests!
Using the DxO testing technology that we developed for our lens review site SLRgear.com, we thought it would be interesting to take a look at the optical quality of the two "Kit" lenses that commonly ship with the Olympus E-500. These tests use the DxO Analyzer program from DxO Labs, together with some back-end graphing and presentation software that we wrote in-house. For details of how we conduct these tests, just what they reveal, and equally importantly, what they don't reveal, visit SLRgear.com, and check out the links covering these topics on the right hand side of the home page.
Meanwhile, the paragraphs below describe the results of our evaluation of the E-500's kit lenses. Click on any of the thumbnail images, to view either the full-size graph, or to launch an interactive viewer to see how blur and chromatic aberration vary as you change the focal length and aperture.
We need to make a very important note about the results seen here, before we actually discuss them. The Blur Index graphs are showing a measure of "softness" that's derived from MTF curves measured at multiple points across the image plane. This measure correlates very well with visual perceptions of sharpness, but is also quite susceptible to variations in the sharpening applied to an image. To remove this factor as much as possible in our measurements, we choose the sharpening setting for each camera that produces the most accurate edge profile, that shows the steepest slope as an edge transitions pixel boundaries, but with the least possible overshoot or undershoot on either side of the edge, caused by the sharpening algorithm. In the case of the Olympus E-500, the default sharpening produced a noticeable "halo" around high-contrast edges, and even the low sharpening setting didn't completely remove this artifact. The impact of in-camera sharpening is generally to generate artificially low blur numbers, so we adjusted the raw values from the DxO tests in order to achieve a good correlation with the results over on SLRgear.com. While you can never make direct 1:1 comparisons between results from different digital camera platforms, we feel confident that the normalization factor we've applied to the results form the E-500 result in a high degree of parity between the results shown here and those we've collected on other platforms in the past. (This serves to illustrate quite well the difficulty of making cross-camera comparisons with the DxO data, and the care needed in doing so.)
Olympus Zuiko Digital 14-45mm f/3.5-5.6
Blur Index |
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| Chromatic Aberration  |
Vignetting (Shading) ) |
Distortion) |
(Click on the thumbnails to see full-size graphs and interactive charts.) |
This is the lens that ships in all kits with the E-500, whether they be single- or dual-lens kits. Offering a range of angular field of view equivalent to that of a 28-90mm lens on a 35mm camera, this is a good general-purpose lens to use with the camera, and the one that most users will probably keep on the camera most of the time.
Looking at the interactive blur plot, we see that the Olympus 14-45 looks a lot like other inexpensive wide angle zoom kit lenses from other manufacturers. (Over on SLRgear.com, you can find test reports for competing optics from Canon and Nikon, if you'd like to compare how they perform.)
Wide open, the 14-45 does quite well in the center of the frame, but gets soft on the edges, particularly toward the middle of its focal length range, at 25-35mm actual focal length. (Note: We think that the increased softness in the upper right corner of the frame may have been caused by a slightly cockeyed chip in the E-500 body we used to do the tests with: The 40-150mm lens showed very similar behavior.) Many inexpensive zoom lenses tend to show softness in the corners of the frame, so this isn't exactly news. What's a bit different about the 14-45 is that it actually does quite a bit better at both the wide angle and telephoto ends of its range than it does in the middle. Also like many inexpensive zooms, the 14-45 settles down quite nicely when you stop it down one or two f-stops. In fact, two stops down (f/5.6 at wide angle to f/8 at telephoto), it actually preforms quite well, comparing favorably with much more expensive lenses. As you stop down further, things stay more or less the same until you get toward f/11 at wide angle or f/16 at telephoto, at which point diffraction limiting begins to have an effect. As usual, stopped down to its minimum aperture of f/22, the entire frame is soft, but at least there's no additional softness in the corners.
Chromatic aberration in the 14-45mm ranges from moderate at wide angle to quite low at telephoto, with relatively little variation across the range of apertures at any given focal length. Matching our own experience when shooting with it, geometric distortion is quite high at wide angle, at nearly 1% barrel distortion, decreasing to almost zero at telephoto. (Interestingly, the distortion always stays slightly to the barrel side of the graph, never crossing over to pincushion distortion.) Finally, uncorrected vignetting or shading ranges from a moderate 0.3-0.4 EV at both side angle and tele focal lengths to less than 0.2 EV in the middle of the zoom range. Vignetting also decreases as the aperture is reduced, remaining below 0.2 EV at f/8 and higher for all but the longest focal lengths.
Important to note is that the in-camera shading compensation offered by the E-500 body can almost completely eliminate the shading or vignetting seen in the above tests.
Overall, this is a pretty decent lens considering the low cost of the camera body and either one or two lenses. Its performance is very much in line with that of the kit lenses for other entry-level d-SLRs that we've looked at.
Olympus Zuiko Digital 40-150mm f/3.5-4.5
Blur Index |
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| Chromatic Aberration  |
Vignetting (Shading) ) |
Distortion) |
(Click on the thumbnails to see full-size graphs and interactive charts.) |
This is the lens that ships in the two-lens kits with the E-500. Offering a range of angular field of view equivalent to that of an 80-300mm lens on a 35mm camera, this is a pretty good telephoto, as long as most users are likely to need for common shooting situations. Thanks to the small dimensions of the Four Thirds sensor, it's also a surprisingly light and compact lens.
Looking at the interactive blur plot, we see that the Olympus 40-150 does pretty well across most of its focal length range, but softness at maximum aperture does increase somewhat as you go from 100 to 150mm. As we've noted with many inexpensive lenses, stopping down two f-stops makes a very significant difference in sharpness across the board, and the 40-150 is actually a very good performer under that condition. As is usually the case, the lens gets softer across the entire frame and at all focal lengths when stopped down to its minimum aperture of f/22. - But the degree of softening there isn't as severe as we've often observed in other lenses.
Where the 40-150mm does get a little wild and woolly though, is in the area of chromatic aberration. Starting out from quite a low value at the 40mm end of its range, CA drops slightly at 48mm and then increases progressively (and rapidly) as you move to longer focal lengths. At 150mm chromatic aberration is rather high, although you'll mostly notice it only around the edges of the frame. Geometric distortion in the 40-150 ranges from a slight barrel distortion at the wide angle end (about 0.3%) to a fairly noticeable (also about 0.3%) pincushion distortion across much of the longer end of its range. (The inflection point of zero distortion is right around 48mm, with pincushion distortion increasing fairly rapidly up to about 68mm, and then more slowly as you zoom to 100mm.) Uncorrected vignetting or shading is pretty high a large apertures across the entire focal length range, varying from 0.25 to about 0.4 EV. The shading decreases quite rapidly as you stop down though, decreasing to less than 0.2 EV at f/5.6 for all focal lengths, and to an imperceptible 0.1EV or less from f/8 onward. (As above, it's important to note that the Olympus E-500 body can almost entirely compensate for lens shading if its shading correction option is enabled.)
Overall, this lens falls about in the middle of the range of inexpensive ~50-200mm zooms that we've tested. It falls short of the surprisingly excellent Nikon 55-200mm f/4-5.6, but beats the Canon 55-200mm f/4.5-5.6 quite handily, particularly at longer focal lengths. When you factor in the very low incremental cost of acquiring this lens as part of a bundled package with the Olympus E-500 body and the 14-45mm f/3.5-5.6, it's an exceptional bargain.
"Supersonic Wave Filter (tm)" Automatic Sensor Cleaning
Here's a feature that made me sit up and take notice on the E-300, and I'm glad to see it included on the E-500 as well: Built-in ultrasonic sensor cleaning! This was first introduced on the E-1 SLR, and has been carried forward to the E-500, 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 to damage the sensor chip.)
In the E-1, E-300, and now the E-500, 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 all three Olympus cameras that use the system.
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 E-500 calls for special comment as well, although the test results we've seen from it and other E-series SLRs from Olympus (which use the same basic sensor technology) lead us 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 cameras with Olympus, they appear poised to regain significant market share for their chips. While Kodak has recently withdrawn their own pro cameras from 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-500 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, E-300, and E-500 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 dSLR models) and 8 megapixel resolution means that the pixels in the E-500's CCD chip are rather small, with a 5.4 micron pitch.
In our testing of the Olympus E-500 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 E-500 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-500. I'd like to see significantly lower noise at ISO 1,600, 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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