Olympus E-420 Optics

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.

 

 

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.

1	AF Targets	7	Auto Exposure Lock
2	Aperture Value	8	Exposure Compensation Value
3	Shutter Speed	9	Metering Mode
4	AF Confirmation	10	Battery Status
5	Flash Status	11	Exposure Mode
6	White Balance

 

 

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