Olympus E-420 Optics

Lens mount. The Olympus E-420's lens mount is compatible with the full array of Four-Thirds mount lenses.

The Olympus E-420 is equipped with an interchangeable lens mount that accommodates the full range of Olympus Zuiko Digital or third party Four-Thirds lenses. A lens release button to the right of the lens mount releases the lens, and a set of alignment marks on the mount itself helps you line up the lens appropriately. Because the camera is compatible with a range of lenses, focal lengths and aperture ranges will vary with the lens in use.

The Olympus E-420's N-MOS sensor is about half the size of a 35mm frame, so the angle of view at any given focal length will not be the same as on a 35mm camera. To find the approximate 35mm equivalent focal length, multiply the focal length of the lens by 2. (Thus, a 50mm lens will provide about the same view as a 100mm lens on a 35mm camera.)

The Olympus E-420 employs a three-point TTL Phase-Contrast Detection autofocus system, and the three AF points are outlined in black in the viewfinder display. Through the LCD menu, you can 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 LCD menu lets you select Manual, Single AF, or Continuous AF modes. There are also options for Single AF and Continuous AF with 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 on the right of 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. The modes combining Single and Continuous AF with Manual focus tell 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.

Like the E-410, the Olympus E-420 always operates in focus-priority mode, where the shutter won't fire unless the subject is properly focused.

Olympus E-420 Live View AF modes

Arguably the biggest advance in the Olympus E-420's design comes in its autofocus system. Olympus pioneered the development of "Live View" in digital SLRs, which has since become a must-have feature for many users upgrading from conventional digicams. While the attraction of an SLR (Single-Lens Reflex) is that the optical viewfinder lets you look through the same lens the camera will take the picture with, digicam users are loathe to give up their big rear-panel LCD viewfinders. Conventional SLR design precludes this, but various manufacturers have found various ways around the issue.

A limitation of Live View in digital SLRs is that the reflex mirror must be raised to expose the main image sensor for viewfinder use. The problem is that this disables the SLR's normal autofocus system, which relies on a secondary mirror and a sensor in the bottom of the mirror box. (It must be noted that Olympus' original Live View DSLR (the E-330) and Sony's most recent Live View models use a secondary image sensor inside the viewfinder optics to avoid this necessity.) As a result, Live View DSLRs have tended to have very sluggish shutter response, because the mirror must be dropped before the exposure in order for the lens to focus. While Live View is an attractive from a convenience and familiarity standpoint, the sluggish shutter response eliminated one of the most important features of SLRs; namely, low shutter lag.

In the E-420 though, Olympus has included an option for contrast-detect autofocus, the same type of autofocus system used in digicams. This may be slower than the phase-detect system the E-420 and other SLRs use for normal focusing, but is likely to be a good bit faster than the conventional Live View system.

Live view in the Olympus E-420 should perhaps come as no surprise: Olympus and Panasonic are partners in subsystem design for Four-Thirds SLRs, and the Panasonic DMC-L10 offered a contrast-detect AF option when it was announced a little while ago. Nikon also introduced contrast-detect AF in their D300, announced last summer. On the D300 though, contrast-detect AF can only shift the lens position rather slowly, leading Nikon to refer to it as "tripod" AF mode.

In fact, via a menu option, the Olympus E-420 offers three different AF options: Phase Detection (the conventional SLR AF technique), Contrast Detection (the normal digicam method), and Hybrid AF (a combination of the two).

The illustration above (click on the image to see a slightly larger view) shows Phase-Detect operation while in Live View mode. Note that the mirror must be dropped every time the focus is adjusted: Once whenever you press the AEL button, and again when you fully press the shutter button to snap the picture.

This set of diagrams illustrates what happens when the Olympus E-420 uses contrast-detect autofocus. The lens can be focused without dropping the mirror, so Live Viewing isn't interrupted to achieve focus: Just half-press the shutter button, and the lens focuses, using signals coming straight from the main image sensor. When you finally do fully press the shutter, the mirror will drop and raise again, but there's no additional time required for focus operation.

Finally, this last set of drawings illustrates Hybrid AF operation: You can focus the lens by half-pressing the shutter button in Live View mode, but when the shot is actually taken, the phase-detection AF sensor will be used.

One benefit of contrast-detect autofocus on DSLRs may not be apparent in the above diagrams: When you're using the main image sensor for focus determination, suddenly you can autofocus on subjects anywhere in the frame, not just where the AF sensors are located. Even more dramatically, main-sensor AF opens the possibility of more intelligent AF modes, such as Face Detection -- which is exactly what Olympus has implemented in the E-420.

Olympus E-420 AF Assist

An AF illuminator option can be turned on through the camera's Custom 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 for this option to be available. The flash can however be disabled, so that natural light images can be captured with AF assist enabled, however this is not as convenient as a dedicated AF assist lamp.

Olympus E-420 Anti-Dust Technology

The built-in Supersonic Wave Filter was first introduced on the E-1 SLR, and has been carried forward to newer models including the E-420. 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-420, every time the camera is turned on, and when starting and stopping live view, an ultrasonic system activates, vibrating the protective cover glass over the sensor, thereby dislodging 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.)

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.

Olympus E-420 Optical Test Results

Below are the results of our optical tests on the Olympus E-420. We used the 14-42mm kit lens as the benchmark, since most people will buy and use the camera in this configuration.



Very good performance from the 14-42mm, 3x zoom lens that comes with the Olympus E-420 kit.

14mm 42mm

The Olympus E-420 digital SLR comes with an Olympus Zuiko Digital ED 14-42mm f/3.5-5.6 lens in the bundled kit, equivalent to a 28-84mm lens on a 35mm camera, about the same equivalent range covered by the 18-55mm kit lenses on SLRs with 1.5x crop factor sensors. Results were very good at 14mm, with minimal corner softness and good detail throughout the frame; though it is slightly soft overall, it's consistent across the frame, and sharpens well. Coma distortion in the trees was quite low, although there is some minor chromatic aberration visible in the corners and edges. Results were even better at the 42mm setting, with no signs of visible coma distortion or chromatic aberration.

An average-sized macro area with the kit lens, though good detail and high resolution. Flash exposure was uneven up close.

Standard Macro with
14-42mm Kit Lens
Macro with Flash

The Olympus E-420's kit lens performed well, though macro performance will vary with the lens in use. With the 14-42mm kit lens, the E-420 captured an average minimum area of 2.72 x 2.04 inches (69 x 52 millimeters). Detail and resolution were both good, though details are a bit soft overall, with moderate softening in the corners. (Most kit lenses have some softening in the corners at macro distances.) You'll get much better results with a dedicated macro lens. The built-in flash produced a dim, uneven exposure here, partially blocked by the lens barrel, so plan on using external lighting for macro shots with this lens.

Moderate barrel distortion with the 14-42mm kit lens at wide angle, though very low distortion at telephoto.

Barrel distortion at 14mm is 0.7 percent
Distortion at 42mm is virtually nonexistent

The Olympus E-420's 14-42mm kit lens produced about 0.7 percent barrel distortion at wide-angle. Though this is slightly below average among the cameras we've tested, we still find it a little high to our eyes. At the telephoto end, the distortion was so low, it was difficult to measure. 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).

Chromatic aberration
Moderate and bright at wide-angle, but very low at telephoto with the 14-42mm kit lens.

Wide: Moderate and bright,
top left @ 200 percent
Wide: Moderate and bright,
top right @ 200 percent
Tele: Very low,
top left @200 percent
Tele: Very low,
top right @200 percent

Chromatic aberration is moderate at the full wide-angle setting of the Olympus E-420's 14-42mm kit lens, showing 6-8 pixels of bright coloration on either side of the target lines. The effect was only slightly noticeable in some images. At full telephoto, this distortion is much fainter and not very evident at all. (This distortion is visible as a slight colored fringe around the objects at the edges of the field of view on the resolution target.)

Corner Sharpness
Minor softening in the corners of the frame at wide angle with the 14-42mm kit lens.

Wide: Slightly soft in the
corners (upper right).
Wide: Sharper at center.
Tele: Hardly any softness in
the corners (upper right).
Tele: Sharp at center.

The Olympus E-420's 14-42mm kit lens produced slightly soft corners in a few shots, but to a lesser extent than we're accustomed to seeing in cameras we test. Corners at wide angle were a little bit softer than at and full telephoto, but the center was also softer at wide angle. Overall, a very good result.


Olympus E-420 Viewfinder

The E-420 has an optical viewfinder, although it's a little cramped. Still, you get something better than Live View mode on the LCD: a true live view of what you're about to shoot, with no electronic delay. A dioptric adjustment dial to the right of the viewfinder accommodates eyeglass wearers, letting them adjust the viewfinder optics between -3.0 to +1 diopters. According to Olympus, coverage is approximately 95%, and our test results agree. The viewfinder has a magnification of 0.92x for a 50mm lens and -1 diopter of dioptric correction. The eyepoint is fairly low: 14mm at -1 diopter.

Three autofocus points are arrayed across the center of the screen. At the right of the screen, the E-420 keeps you posted about its settings and status, including Aperture, Shutter speed, Focus confirmation, Flash status, Exposure compensation, Metering mode, Battery status, and Exposure mode. See the complete list below.

AF Targets
Auto Exposure Lock
Aperture Value
Exposure Compensation Value
Shutter Speed
Metering Mode
AF Confirmation
Battery Status
Flash Status
Exposure Mode
White Balance


Viewfinder Test Results

Good accuracy with both the optical viewfinder and LCD monitor's Live View mode.

14mm, Optical
42mm, Optical
14mm, LCD
42mm, LCD

The Olympus E-420's optical viewfinder proved fairly accurate, at just over 95% at both wide angle and telephoto (with the 14-42mm kit lens), though it's not quite centered with respect to the image sensor. The camera's Live View LCD mode was very accurate, with about 100% accuracy at both wide angle, and telephoto.


The images above were taken from our standardized test shots. For a collection of more pictorial photos, see our Olympus E-420 Photo Gallery .

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