Sony NEX-3 Optics
Sony NEX-3 Optics
Sony E-mount Lenses
Much like the Micro Four Thirds format pioneered by Olympus and Panasonic, and the NX format from Samsung, Sony's E-mount standard is designed to significantly reduce the size and weight of interchangeable lens digital cameras, by eliminating the bulky mirror box from the design. With the mirror box gone, the "back-focus distance" (or back focal length) of compatible lenses can be reduced. Technically, back focus distance is defined as the distance from the vertex of the lens's rear element to the sensor, but for practical purposes, it's easier to speak in terms of the distance from the lens-mounting flange to the sensor surface. In the existing Alpha (A-mount) DSLR system, this dimension was 40mm. For the Sony E-mount, it has been slashed to just 18mm. That's significantly less than the 25.5mm flange-back distance of Samsung's competing NX format, and it's even a little less than the 20mm flange-back of Micro Four Thirds. This despite Sony's use of the same APS-C sensor size as in its Alpha DSLRs (also shared by Samsung's NX format), which is some 60% greater in area than the smaller Four Thirds sensors used by Panasonic and Olympus. The decreased flange back distance has allowed Sony to significantly reduce both the size and weight of the camera body, as compared to its Alpha DSLRs.
That's not the only benefit, though. Like its rival formats, the Sony E-mount offers not only the possibility of smaller and lighter camera bodies, but also of a significant reduction in the size and weight of the lenses. While the physical size of a lens depends somewhat on the size of the image circle it must produce, it also depends strongly on the back focus distance the lens was designed for. Reducing the back focus distance can significantly decrease the length of the lenses needed to cover the area of an APS-C image sensor. Lenses for the new system can also be somewhat smaller in terms of diameter as well, and indeed the new mount is just slightly smaller than those of Sony's existing Alpha (A-mount) lenses. The maximum dimension of an E-mount lens flange is 1.815" (46.1mm), versus 1.939" (49.7mm) for A-mount lenses.
Removing the mirror box does have some potential disadvantages, though. Obviously, it removes the possibility for any E-mount camera to offer a true through-the-lens optical viewfinder, with no way to divert the optical path to the viewfinder between exposures. Just like Micro Four Thirds and NX designs, Sony E-mount cameras are limited solely to using a Live View mode, where data streaming from the image sensor is used to provide a preview image for framing. For current NEX-series cameras, the LCD display is the sole option for live view, as Sony doesn't offer an electronic viewfinder. (The FDA-SV1 viewfinder accessory is an optical viewfinder with its own separate objective lens.)
Likewise, with nowhere in the optical path to put dedicated sensors for metering or phase detection autofocus, E-mount cameras are reliant on the image sensor itself for both functions. This means using contrast detection autofocus, which can offer higher focusing accuracy (and negates problems with front or back focusing), but is typically rather slower than the phase detection systems found in digital SLRs. Since contrast detection relies on stepping the focus and confirming whether contrast at the AF point has increased or decreased as a result, this also places rather greater demands on the lens' focus drive mechanism.
To improve contrast detection AF performance, Sony has reduced the weight and adjusted the positioning of the focusing group in its new E-mount lenses, while focus drive is provided by a stepper motor. With NEX-series cameras also featuring video recording capability, another important design factor for Sony was to ensure that the sensitive onboard microphone didn't pick up focusing noise. Thankfully, the new focus drive is pretty near silent, which couples with its speed to make autofocus a genuinely useful proposition in video recording. A second stepper motor is used for electromagnetic iris control, and this too is near-silent).
Because of the demands of contrast detection AF, NEX-series cameras only offer autofocusing when using E-mount lenses, which have been designed with these requirements in mind. Alpha-mount lenses attached courtesy of the optional LA-EA1 mount adapter (priced at $199) can only be focused manually, with no autofocusing possible. (Note that NEX firmware update version 03 adds autofocus support when using a variety of Sony's Alpha-mount lenses on NEX-series cameras using the LA-EA1 mount adapter, once the adapter firmware itself has been updated to version 02. See our NEX firmware news article for details with links to the firmware downloads.) It also doesn't allow SteadyShot stabilization, and its use reduces continuous burst speed. The good news is that the mount adapter does pass aperture information between the attached lens and camera body, and is compatible with all Sony's Alpha-mount lenses. (Third party lenses may or may not work with the adapter, depending on how closely they mirror the design of Sony's own lenses.)
The initial three lenses for the Sony E-mount system all feature all-metal construction with aluminum lens barrels, and steel mounts. Both zoom lenses offer optical image stabilization, with the E 16mm f/2.8 lens (model SEL16F28) being the sole model to forgo image stabilization. For that small sacrifice, it's also the smallest and lightest E-mount lens thus far, as well as offering the closest focusing of the group. The stabilized E 18-55mm F3.5-5.6 OSS lens (model SEL1855) has the same barrel diameter, but is just a little under triple the length and weight. Usefully, the 18-55mm lens accepts the same 49mm filter threads as the prime -- doubly helpful because it means the pair can also share lens caps, saving fumbling in your pocket for the second cap every time you switch lenses. Finally, the E 18-200mm F3.5-6.3 OSS lens (SEL18200) offers by far the most telephoto reach of the trio. Featuring the more powerful SteadyShot Active stabilization system, the E 18-200mm also provides the highest maximum magnification of the trio, at approximately 0.35x. It's also the largest of the group, with a barrel diameter that tapers outwards a little over 20% wider than its siblings, and being two thirds longer than the 18-55mm lens. It also weighs over two and a half times more than the 18-55mm lens, and takes a significantly larger 67mm filter thread.
Full specifications for each of the three lenses are as follows:
Full specifications for the mount adapter and conversion lenses are as follows:
Sony NEX-3 Autofocus
The Sony NEX-3 has a 25-area contrast-detect autofocus system, using the main imaging-sensor to determine focus, similar to how most Point & Shoot cameras work. There are three AF Area options: "Multi" mode, where the camera automatically selects the active area(s) for you, "Center", where only the single AF point at the center of the image frame is used, or "Flexible Spot" mode, where you specify the active area by selecting it with the 4-way controller. This last mode provides greater positioning accuracy and a smaller AF point, which can be placed anywhere within a 17 x 11 grid that fills most of the image frame, except for the extreme edges.
In addition, the NEX-3 offers a Face Detection function, capable of simultaneously locating up to eight individual faces. The face selected by the camera as being the main subject is outlined with an orange frame, and is then taken into account when focusing and metering. Each additional face that the camera finds is indicated on the display or electronic viewfinder with a white frame. Much like the Flexible Spot AF mode, you're not limited to the NEX-3's 25 autofocus points - the camera will lock focus on a face anywhere within the frame except for the extreme edges. It can also differentiate between the faces of adults and children, and while the NEX-3 can't recognize specific individuals' faces, it can at least prioritize either the kids, or the grown-ups. The Face Detection capability is also used to offer a Smile Shutter mode, which can automatically trip the shutter when at least one person in the image frame is smiling -- and the degree of smile that's required for the shutter to be tripped is adjustable in three steps.
The NEX-3 includes a bright orange AF assist illuminator adjacent to the Sony logo on its front panel, which can be very helpful with attaining a focus lock in poor ambient lighting, at least for nearby subjects. The same lamp also functions as an indicator for the camera's self-timer and smile shutter functions. If its use might prove distracting or objectionable, such as in a museum or place of worship, the AF illuminator can be disabled altogether. Note that even when disabled for AF assist, the lamp will still function for self-timer or smile shutter shooting, however.
Of course, the Sony NEX-3 also offers manual focusing - either as the sole focusing method, or for fine-tuning focus once AF is complete. In the manual focus modes, an option called MF assist optionally causes the camera to magnify the preview image by either 7x or 14x, whenever the focus ring is adjusted. The zoom level is adjusted by pressing a soft key, and MF assist preview is centered around either the user-selected focus point in Flexible Spot or Center modes, and around the AF point selected by the camera in Multi AF. (If more than one AF point is considered to be in focus, then the camera selects one of these points around which to base the preview, although we're not exactly sure what the criteria for choosing the center point is.) Given that Alpha (A-mount) lenses offer only manual focusing through the mount adaptor, MF Assist will prove doubly useful for owners of Alpha digital SLRs who want to share their glass between bodies. Of course, while the fly-by-wire E-mount lenses can tell the camera when focus is being adjusted, this isn't possible with A-mount glass, so the MF Assist function must be manually triggered when needed.
As we note elsewhere, the LCD on the NEX-3 is superb, with great contrast and an extremely high resolution of 921.6K dots. It's also generously sized, with a 3.0" diagonal, and can automatically account for ambient lighting to adjust its brightness. Add in its double-hinged tilt mechanism for shots overhead or low to the ground, and the NEX-3 becomes a joy for precise manual focusing, from most any angle.
As well as manual focus, Autofocus servo modes consist of single shot or continuous autofocus. In S-AF mode, focus is locked along with the exposure when the shutter button is half-pressed, and this behavior can't be changed. If you want to meter off one subject, but focus on a subject at a different distance, the only workarounds are to use continuous autofocus, or one of the manual focus modes. In continuous AF mode, the camera continuously cycles its AF system, which helps it track moving objects, keeping the current lens focal distance setting closer to the current subject distance than it might otherwise be. This can reduce AF "hunting" when it comes time to snap the actual shot. Because contrast-detect AF systems have to perturb the focus in order to tell whether the image is actually in focus or not, the NEX-3's Continuous-AF mode disturbs the viewfinder display on the LCD while it's operating. That is, the viewfinder image continuously shifts in and out of focus when C-AF is active, as the camera constantly re-checks its focus setting. This is a necessity for any contrast-detect AF system, but the amount of defocusing required by the NEX-3 is subjectively a little less than we've seen in some other systems. It does seem to vary by subject even with static scenes though, with some scenes provoking only a modest but frequent shuffling of the focus point, where other subjects prompt less frequent (but more dramatic) shifts in focus.
AF in Movie mode
In Movie mode, the NEX-3 offers a choice of either continuous autofocus, or manual focus, and appears to use multiple-point focusing. The AF system seems to respond more slowly to changes in subject distance, and to make the focus adjustment at a reduced rate compared to still-image shooting, but the AF operation is relatively smooth and for the most part free of the hunting that's seen with continuous AF in still image mode. Thanks to the aforementioned E-mount lens design, focus motor operation isn't picked up by the camera's internal microphone, making both autofocus and fly-by-wire manual focus a useful proposition. (You do have to be careful about handling noise while you're holding the camera, if adjusting focus manually, of course.).
Sony NEX-3 Sensor Cleaning
The Sony NEX-3 features an electromagnetic vibration dust-reduction system, coupled with a charge protection coating on its low-pass filter that aims to prevent dust adhering -- especially important since the NEX-3's shutter is normally open for full-time Live View. The vibration seems to be at a rather lower frequency than some competing systems (or perhaps to have a harmonic at a lower frequency), because it's clearly audible as a brief, high-pitched whine when operating. Intelligently, the system automatically runs only at power-off, meaning that it doesn't delay camera startup. It can also be triggered at any time while using the camera, should you notice that dust specks are present in your images.
We have found, however, that in-camera dust-removal systems are less than perfectly effective. You're still going to need to use a sensor-cleaning kit fairly often, so the advantage of in-body dust removal is perhaps less than it might seem. If you've got dust specks on your sensor (and sooner or later you will), you're going to need to clean it. There are a lot of products out there intended to address this need, but a distressing number of them work poorly (if at all), and many are grossly overpriced. Advertising hype is rampant, with bogus pseudo-scientific jargon and absurd product claims. And prices -- Did I mention prices? How about $100 for a simple synthetic-bristle brush?
So how do you know what product to use?
We don't pretend to have used everything currently on the market, but we can tell you about one solution that worked very well for us. The "Copper Hill" cleaning method is straightforward and safe, and in our routine usage here at Imaging Resource, highly effective. Better yet, the products sold by Copper Hill Imaging are very reasonably priced. Best of all, Nicholas R (proprietor of Copper Hill) has put together an amazingly detailed tutorial on sensor cleaning, free for all.
Sensor cleaning is one of the last things people think about when buying a d-SLR, but it's vital to capturing the best possible images. Take our advice and order a cleaning kit from Copper Hill right along with your d-SLR, so you'll have it close at hand when you need it: You'll be glad you did!
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Optics Test Results
The Sony NEX-3 is available bundled with either the 18-55mm f/3.5-5.6 OSS lens for $650, or the 16mm f/2.8 prime for $550. Below are test results from both lenses mounted on a NEX-3.
Lens Test Results
Good performance with the 18-55mm OSS kit lens.
|18mm @ f/8||55mm @ f/8|
The Sony NEX-3 is available bundled with the Sony E18-55mm f/3.5-5.6 OSS lens, the first E-mount zoom lens. This lens possesses a very typical optical zoom ratio of about 3x, with a 35mm equivalent focal range of about 27-83mm because of the NEX-3's 1.5x "crop factor." Results were good at 18mm with strong detail across most of the frame, though there was some softening in the extreme corners, even at f/8. Coma distortion in the trees was moderate in the corners, as was chromatic aberration along high contrast elements near the edges of the image. Results were similar at the 55mm setting, with good sharpness across most of the frame, but extreme corners were soft. Chromatic aberration at full telephoto was negligible. Overall, good results for a kit lens, and the built-in image stabilization should come in handy for low-light shooting.
16mm: Good results with the 16mm f/2.8 lens.
|16mm f/2.8 lens @ f/8|
Also available bundled with the NEX-3 is the Sony E16mm f/2.8 lens. Its equivalent focal length is 24mm, which is wider than most kit lenses. It performs similar to the 18-55mm lens with fairly sharp detail across most of the frame, but with moderate softness in the extreme corners, as well as moderately high levels of chromatic aberration. This is a good (but not great) performance for a wide prime. Note that the 16mm f/2.8 lens is not optically stabilized.
The Sony NEX-3 offers up to 10x precision digital zoom (interpolated) when a prime lens is attached, however we did not test that feature.
18-55mm: An average minimum coverage area (for an SLD* zoom kit lens), with soft detail overall. Flash did a pretty good job throttling down.
18-55mm kit lens @ f/5.6
|Macro with Flash|
As with zoom performance, the Sony NEX-3's macro performance will depend entirely on the lens in use. However with the 18-55mm kit lens set to 55mm, the Sony NEX-3 captured an average minimum area measuring 2.97 x 1.98 inches (76 x 50 millimeters). Detail was quite soft in the center, and the corners were softer still. (Most lenses have some softening in the corners at macro distances.) The detachable flash did a pretty good job throttling down, resulting in just a slightly overexposed image. The flash had no trouble clearing the lens, though, as there is no detectable shadow.
*SLD = Single Lens Direct-view
16mm: Very large minium area, but with excellent detail in the center. Flash coverage was uneven.
16mm f/2.8 lens @ f/5.6
|Macro with Flash|
With a very large minimum coverage area of 10.9 x 7.2 inches (278 x 183 millimeters), the 16mm f/2.8 makes a very poor "macro" lens. Detail was very good in the center of the image, but there was significant softening in the corners that extended fairly deep into the frame. Flash coverage at this distance is very uneven.
18-55mm: Higher than average geometric distortion at both wide-angle and telephoto.
|18-55mm: Barrel distortion at 18mm is 1.1 percent|
|18-55mm: Pincushion distortion at 55mm is 0.4 percent|
The Sony NEX-3's 18-55mm kit lens produced about 1.1 percent barrel distortion at wide-angle, which is higher than average and noticeable in some of its images. At the telephoto end, there's about 0.4 percent pincushion distortion, also slightly higher than average but not as noticeable in images. This is the tendency for the lens to bend straight lines outward (like a barrel -- usually at wide-angle) or inward (like a pincushion -- usually at telephoto).
16mm: Moderate geometric distortion.
|16mm f/2.8: Pincushion distortion is 0.5 percent|
The Sony 16mm f/2.8 lens showed about 0.5% pincushion distortion, which is a little high for a prime, but reasonable for a wide-angle lens. The distortion is complex, with most of it occurring near the corners. It's unusual to have pincushion distortion in a wide-angle prime lens, though, as most have barrel distortion.
The Sony NEX-3 does not appear to be applying any geometric distortion correction to its JPEGs, as uncorrected RAW files show the same amount of distortion.
Chromatic Aberration and Corner Sharpness
18-55mm: Moderately high chromatic aberration at wide-angle; much lower levels at full telephoto. The lens produced some soft corners.
Chromatic Aberration. Chromatic aberration in the corners with the NEX-3's 18-55mm kit lens at wide-angle (18mm) is moderate in terms of the number of pixels, but quite bright, so the effect is noticeable. At full telephoto (55mm), C.A. is also moderate in terms of pixels, but the colors in the fringes are quite muted, partially due to loss of contrast. Color fringing gradually reduces in brightness and width as it approaches the center of the image, where it is almost nonexistent at both full wide-angle and full telephoto.
Corner Softness. The Sony NEX-3's 18-55mm kit lens produced some soft corners in most shots. At full wide-angle the left-hand corners exhibited moderate blurring, with the top left corner being the softest. The center of the image was sharp with good contrast. At full telephoto, the top corners were quite soft and suffered from a loss of contrast, and the softness extended pretty far into the frame from the left side. The bottom was better but still soft in the extreme corners, while the center was slightly soft. A slightly below average performance overall for a kit lens here. (Note that the lens was "wide-open" for these shots, and corner sharpness generally improves when a lens is "stopped-down" a couple of f-stops below full aperture.)
16mm: Moderately high chromatic aberration and strong blurring in extreme corners.
|16mm f/2.8 lens @ f/2.8|
|Wide: Lower right
C.A.: Moderately high
Softness: Strong blurring
Chromatic Aberration. Chromatic aberration with the 16mm f/2.8 lens is moderately high in the corners, and it extends fairly far into the frame where it reduces overall sharpness and definition. Some minor chromatic aberration is visible in the center as well.
Corner Softness. The Sony 16mm f/2.8 produced strong blurring in the extreme corners, with the right-hand side corners being slightly softer than the left. Though the extreme blurring didn't extend very far into the frame, there was some softness across much of the frame, except near the center which was fairly sharp and contrasty. There also appears to be a fair bit of vignetting in the corners, as they are noticeably darker than the center. Keep in mind these shots were taken with the lens wide-open, and that corner sharpness and vignetting improve when the lens is stopped-down a bit. See: NEX3hVFA16L.JPG for the same target, but with the 16mm lens stopped down to f/5.6.
The Sony NEX-3 doesn't appear to be applying any chromatic aberration in its JPEGs, as uncorrected RAW files show similar amounts.
The images above were taken from our standardized test shots. For a collection of more pictorial photos, see our Sony Alpha NEX-3 Photo Gallery .
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