Sony NEX-3 Optics

Sony NEX-3 Optics

Sony E-mount Lenses

The Sony NEX-3 features a new lens mount dubbed the Sony E-mount, and at launch, Sony is offering three E-mount lenses compatible with its NEX-series camera bodies -- a 16mm f/2.8 prime, an 18-55mm f/3.5-5.6 zoom, and an 18-200mm f/3.5-6.3 zoom. Two conversion lenses specific to the 16mm prime increase the wide-angle possibilities for E-mount photographers. In addition, the NEX-3 is also compatible with the company's Alpha (A-mount) lenses courtesy of an optional adapter. Thanks to its use of an APS-C sized image sensor, the NEX-3 has a 1.5x focal length crop. Given that the Sony NEX-3 and NEX-5 are the first E-mount cameras to be announced, it might be good to take a quick look at just what the E-mount is all about.

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!

(While they've advertised on our sister site SLRgear.com from time to time, we receive no promotional consideration from Copper Hill for this note. We just think their sensor cleaning products are among the best on the market, and like their way of doing business. -- We think you will too. Click here to check them out.)

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.

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 .