If you’ve read my reviews before, you may notice that I always discuss sharpness first, but I’m switching things up for this review because the discussion on distortion will impact the discussion on the other imaging parameters. The reason for this is that when viewing uncorrected RAW files, the 18-105mm f/4 G OSS has the worst distortion characteristic of any lens I have ever used for any format. The lens exhibits moderate pincushion distortion at 18mm and it simply gets worse from there, with more severe pincushion throughout the zoom range. The level of distortion is rather extreme, and is actually somewhat more complex than typical pincushion distortion, as using standard distortion correction tools will still leave residual bending of lines at the image edges.
The distortion is severe enough that I view the digital correction of this distortion to be absolutely essential to using the lens. The distortion is visible not only in shots of architecture and other images with straight lines, but can even be noticeable in portraits or more abstract work. It has the potential to ruin images if left uncorrected.
Luckily, if you are shooting JPEG images or shooting videos on a more recent E-Mount body, the camera will apply built-in distortion correction to the images, and this correction is even displayed when the camera is showing you the live view. Additionally, Lightroom 5 has a profile for this lens that corrects the distortion perfectly, which I would highly recommend applying upon import if you are shooting RAW. As such, after discovering this and setting an import preset to apply profile corrections, I don’t ever see the distortions any more in practice.
View the two images to the right, showing uncorrected and corrected levels of distortion. I would not recommend using the 18-105mm if you are shooting RAW and you typically use a RAW converter that doesn’t have a profile for this lens.
The reason I discuss this first, is that the evaluation of all the other imaging qualities in this review is based on images that have had the digital distortion correction applied. I didn’t bother evaluating sharpness on uncorrected images because in my opinion, images from this lens are essentially useless without correcting the distortion. As such, sharpness and CA was evaluated after applying the profile corrections in Lightroom 5.4.
So, given the ‘G’ designation on this lens, I expected a relatively high level of sharpness from this lens, and I have to say, it didn’t quite meet my expectations, though it wasn’t too far behind. The 18-105mm f/4 is a lens that provides very good sharpness over the central 80% of the frame throughout the range, right from f/4. However the edges and corners do lag a bit behind at f/4. Stopping down brings edge and corner resolution at most focus distances to ‘good’ territory, but never into outstanding territory.
The lens is the weakest at the wide end of the zoom range, with the edges of the frame retaining a bit of softness even stopped down, though for most shooting there is plenty of detail across the vast majority of the frame, and the center is excellent. Click on the image to the left and then click on the green arrow to enlarge to see a large sample. The mid range towards the long end of the zoom sees some improvement overall, with a very good performance here, with just a slight bit of corner softness. The center softens slightly at 105mm, but still provides acceptable results, though image borders at 105mm remain only average stopped down.
The best way to sum up the sharpness of this lens is to say that it is always competent, but rarely exceptional.
Wide range standard zooms are usually not renowned for their excellent bokeh, but the 18-105mm does a very nice job in this department. With a longer range than most standard zooms, the f/4 aperture will still allow for a fair bit of background blur, and when blurring the background, the 18-105mm produces quite pleasing bokeh. Out of focus areas are generally smoothly rendered and specular highlights are round and evenly lit. ‘Onion’ rings in the highlights can occasionally be observed due to the aspherical elements in the lens, but overall, a very nice performance that stays consistently good at all focal lengths.
Color, Contrast, Flare and Aberrations
The 18-105mm provides a very neutral output with regards to contrast, with somewhat muted midtones. The result is a file that can be tweaked to your desire, but won’t provide huge amounts of pop right out of the camera. Color on the 18-105mm tends towards the cool side, with color saturation being neither dull nor extremely rich. While this means that straight out of the camera, you may need to add some minor contrast and saturation tweaks, it also means that you’ve got a great starting file from which to work.
Overall, the lens performs pretty well against bright light. Some minor flare ghosting can occur in the right circumstances, but overall the lens does a nice job here. In the right circumstances, some lateral chromatic aberration can be visible, though I found it rarely posed an issue in everyday shooting. Indeed, I have to go looking for it for the most part. A lot of this is not so much that the absolute level of CA is low, but rather that for some reason, where it shows up, the saturation of the fringe isn’t particularly high, so it often blends into the adjacent detail without issue.