Olympus TG-4 Optics

Zoom
A 4x wide-angle zoom, with about average performance for its type.

The Olympus TG-4 is equipped with a 4.5-18mm lens, offering an optical zoom ratio of 4x, translating to a 35mm-equivalent focal range of about 25-100mm. The lens is quite fast (bright) at the wide end, with a maximum aperture ranging from f/2.0, however at the tele end maximum aperture is a bit dim at f/4.9.

The TG-4's lens features a 1-stop diaphragm plus 3-stop ND filter aperture mechanism, offering settings of f/2, f/2.8 and f/8 at full wide angle, and f/4.9, f/6.3 and f/18 at full telephoto. (The ND filter cannot be enabled with the diaphragm wide open.) The following table reflects the maximum and minimum apertures as reported by the camera at popular approximate focal lengths:

Far-field performance is about average for its type, which is to say decent but not great. (Apologies for the poor color and exposure -- the blue sky and snow tricked the camera's auto white balance and metering.) At maximum wide angle, sharpness is quite good in the center, but corners are soft and there's some noticeable purple fringing. The lens isn't as sharp at full telephoto and there's still some noticeable purple fringing, but the corners are reasonably sharp. Since the optical zoom ratio is only 4x, we've included a shot with 2x digital zoom above. It actually performed better than average, but the resulting image is quite a bit noisier.

See below for lab results on macro performance, geometric distortion, corner softness, etc.

Macro
A much smaller than average sized minimum coverage area, with very good detail in the center. Flash throttled down well, but illumination is not even.

The Olympus TG-4 captured a much smaller than average sized minimum area measuring only 0.96 x 0.72 inches (24 x 18 millimeters) when using Microscope mode. Sharpness in the center of the frame is pretty good, however corners and edges are quite soft (most lenses show some softening in the corners at macro distances). Note that the TG-4 does not let you adjust the aperture in Microscope mode, and the camera shot wide-open at f/2.3 without flash, and at f/6.3 with the flash. The flash did a good job throttling down, but illumination was not even and the camera's red body caused lighting to take on a red tint on left side, likely due to reflections (this also happened without flash, but to a lesser extent).

Geometric Distortion
Very low distortion in camera JPEGs, but very high in uncorrected RAW files at wide angle.

Thanks to in-camera distortion correction, there's very little geometric distortion in the TG-4's JPEG files, though what distortion there is asymmetrical. At full wide angle, we measured about 0.1% barrel distortion along the top edge, but about 0.2% pincushion distortion along the bottom edge. At full telephoto, barrel distortion along the top edge is much less than 0.1%, increasing to about 0.2% along the bottom edge. Still, very low geometric distortion overall. 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).

To see how much correction is taking place in the camera, we converted RAW files from the above shots with RawDigger, which does not correct for distortion. At wide angle, barrel distortion is very high, between 3.1 and 3.5% depending on which edge is measured, while telephoto varies from 1.0 to about 1.2% pincushion depending on which edge.

We expect to see fairly significant distortion in uncorrected RAW files in fast, compact lenses, as allowing this gives the lens designers greater flexibility in optimizing center sharpness and other aberrations, as well as in reducing cost, size, and weight. The downside is that the distortion correction contributes additional blurring to the corners of the frame where pixels are "stretched" during correction and where lenses are usually already a bit soft. Note that most RAW converters are capable of applying distortion correction automatically, as specified by the manufacturer in a lens profile built into the TG-4's RAW files.

Chromatic Aberration and Corner Sharpness
Moderate chromatic aberration in JPEGs. The lens produces some soft corners, though corner sharpness improves stopped-down.

Chromatic Aberration. Thanks to in-camera chromatic aberration suppression in JPEGs, there's moderate lateral chromatic aberration in the corners at wide angle and fairly low CA at telephoto. At wide angle, there's moderate amounts of blue and yellow fringing while at telephoto, there is milder magenta fringing. As expected, though, uncorrected RAW files (see below) show much more CA than seen above.

Corner Softness. Wide-open at full wide angle, the exhibits extreme corners that are quite soft, and some softening extends into the frame about a quarter of the way. Most of the frame is pretty sharp, though, including the center. Wide-open at full telephoto, corner sharpness is better all around, but contrast isn't quite as good. The center is fairly sharp, but again shows lower contrast than at wide angle.

Vignetting. There's some moderate vignetting (corner shading) wide-open, shown by how much darker the corner crops above are than those from the center, at both wide angle and telephoto

Stopped-down: Stopping down to f/2.8 (one stop) improved corner performance at wide angle, however corners were still much softer than the center. Contrast and vignetting in corners improved along with sharpness, though chromatic aberration remained moderate. The center also became slightly sharper at f/2.8. While contrast, chromatic aberration and vignetting improved in the corners at full telephoto when stopping down one step, sharpness actually fell due to diffraction at f/6.3. Sharpness in the center also fell, but contrast and CA improved. Note that "stopping down" further to the minimum "apertures" of f/8 at wide angle and f/18 at telephoto uses a 3-stop ND filter to avoid additional diffraction, though we did find it reduced sharpness at the telephoto end in real-world shots.

Chromatic Aberration Correction

As you can see in the crops from uncorrected RAW images on the right (taken from .ORF files converted with Adobe Camera Raw which didn't correct for chromatic aberration by default), the TG-4's lens produces fairly high and bright chromatic aberration at maximum wide angle, but it's much lower at full telephoto. The TG-4's processor does a decent job suppressing CA in camera JPEGs (crops on the left), though it does leave some behind and shifts the colors due to slight overcorrection.

Overall, about average optical performance for its class with good sharpness in the center at maximum wide angle but with soft corners, a noticeable drop in sharpness and contrast at full telephoto, and a lot of digital corrections applied to in-camera JPEGs.

Coverage
Very good accuracy from the LCD monitor.

The Olympus TG-4's LCD monitor provided close to 101% coverage at full wide angle and at full telephoto. This is very good performance, especially considering the amount of geometric distortion correction taking place.