Focus Performance and Accuracy
Having fast and accurate autofocus is an essential feature of a standard zoom lens. These days even the most basic lenses offer a solid focusing performance, but where the top of the line lenses come into their own (along with the better camera bodies) is in being able to focus accurately under challenging conditions. Conditions such as low light, fast-moving subjects, and complex backgrounds require lenses that make the most of the cameras tracking capabilities, and thankfully the Sony EF 24-105mm f/4 G OSS does an excellent job in this regard.
The focusing system relies on Sony’s Direct Drive SSM which is both fast and silent. I did notice some hunting with the lens in low light situations (around ISO 12,800), but in such scenarios the limitations of an f/4 max aperture become apparent. An important aspect to remember when judging a lens focusing ability is that the camera body plays an integral role in the quality of the autofocus and because of this, it is essential to match your lenses with high-quality bodies that can deliver an excellent focusing performance. I was able to test the FE 24-105mm f/4 G OSS alongside the very good Sony Alpha A7III body whose focusing capabilities make the most of the lens. The combination focuses accurately with very high consistency, while also remaining very quiet.
When shooting in AF-S single shot mode, the camera needs to de-focus the lens before focusing on the subject which leads to noticeably slower performance than using Continuous Autofocus. Still, overall focus speed is good enough for most uses, and the accuracy is very high even in relatively low light.
Some users of this lens have experienced issues of focus shift as you stop down when using it in AF-S mode. In AF-S mode, Sony cameras focus with the aperture wide open (to enable more light to reach the sensor), and some samples of the lens showed a significant focus shift due to this. I couldn’t replicate this result with my copy of the lens, and the problem seems to be serial number dependent.
Switching to AF-C continuous focus mode significantly speeds up focus acquisition but at the cost of a lower consistency in accuracy as the camera now uses the shooting aperture (This allows the camera to instantly respond if you press the shutter release, with no delay waiting for the aperture to stop down). While overall accuracy is certainly reduced while using AF-C compared to AF-S, I found the overall performance to be on a high level.
Sony’s unique inclusion of an AF-hold button in a lens of this type, which can be pressed to lock focus at the current focus distance, enables you to use the focus and recompose technique while the camera is in AF-C continuous focus. This is highly beneficial if the cameras focus coverage does not extend out to the corners of the frame to cover your subject (a rarity with the most recent Sony mirrorless camera bodies). The button also acts as a custom button (C5) and can be programmed to do a number of different functions using the camera’s menu.
The manual focus ring is located forward of the zoom ring which is my preferred position. The ring is well dampened and offers a 193° rotation amount which allows for precise manual focusing. Manual focus works by focus-by-wire which is implemented quite well in this lens, but it can be an acquired taste for someone used to mechanical manual focus implementations.
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