by Klaus Schroiff, published December 2017
Introduction
Recently, we reviewed the Zeiss Batis 85mm f/1.8 – as it turned out, it’s quite an awesome lens. However, the Zeiss lens isn’t alone in its quest – it has a couple of Sony mates. There’s the insanely expensive 85mm f/1.4 GM and a more mainstream option, which we’ll discuss here – the Sony FE 85mm f/1.8. Some readers may not be too excited about it but as you will see later on it has its merits. Technically, an 85mm f/1.8 is a sweet spot in lens design. It is neither fast nor long enough yet to run into difficult optical correction issues. The Sony lens also avoids the complexities that come with an image stabilizer thus the design is very simple … and simple is often beautiful (…). Priced at around 600USD/EUR it is unusually affordable by Sony standards so this time we’ll not complain about it. 😉
One of the positive aspects of the “sane” speed is the resulting compact size – unlike e.g. the Sony FE 85mm f/1.4 GM it doesn’t feel alien on tiny mirrorless cameras. However, it is worth pointing out that it isn’t any smaller nor more light-weight than its DSLR counterparts. In terms of construction, the lens surprises us with a quite impressive build quality. It’s an all-metal body including the smoothly operating focus ring. The physical length remains constant throughout the focus range. Interestingly, Sony also incorporated a dust- and moisture-resistant sealing. A focus-hold button can be customized to a variety of functions. A barrel-shaped lens hood is also part of the package.
A question circles around the actual focal length of the lens. We tested the Zeiss Batis 85mm f/1.8 and the Sony lens side-by-side and the tele effect is clearly more pronounced on the Zeiss lens. Thus the Zeiss lens is either longer than 85mm or the Sony is shorter – we weren’t able to determine that. That being said it doesn’t really matter in the real world.
The Sony lens uses a Direct Drive SSM (a double linear motor) for auto-focusing. It is silent, fast and fairly smooth so that it is also feasible for getting used during movies (albeit most will prefer manual focusing in this case). Manual focusing works “by wire” thus you drive the focusing motor by turning the focus ring. The manual focus precision is good.
| Specifications | |
|---|---|
| Optical construction | 9 elements in 8 groups inc. 1x ED element |
| Number of aperture blades | 9 (circular) |
| min. focus distance | 0.8m (1:7.7) |
| Dimensions | 78x82mm |
| Weight | 371g |
| Filter size | 67mm |
| Hood | supplied, barrel-style, bayonet mount |
| Other features | Dust- and moisture resistent, focus-hold button |
Distortion
Image distortions are very well controlled. The RAW distortion is already low at just ~0.6% (pincushion style). When activating image auto-correction, the distortion is negligible.
Vignetting
In the Zeiss Batis 85mm f/1.8 review we were somewhat concerned by the very high vignetting – a Zeiss trademark. The Sony FE 85mm f/1.8 isn’t great either in this respect but it does a better job nonetheless. The RAW vignetting is clearly visible with a light falloff of 2.2EV (f-stops) at fully-open aperture. Stopping down to f/2.2 reduces that quite a bit but it takes f/2.8 to push it below the 1EV (f-stop) mark. If you use image auto-correction, the vignetting is reduced by 1.3EV to ~0.9EV (f-stops) at f/1.8 (thus the image noise increases accordingly) which is quite acceptable.
MTF (resolution)
It may come as a surprise to some but the Sony FE 85mm f/1.8 is tack sharp and it rivals the Zeiss Batis in this respect. The goodness starts straight at f/1.8. The quality is already so high that the image quality doesn’t really increase anymore when stopping down. Interestingly the characteristic also mirrors the Zeiss lens at smaller aperture settings. Diffraction kicks in “too late” thus it seems as if there’s an inaccuracy in the aperture mechanism – this may also explain why we had to compensate for an overexposure during our vignetting tests at these settings.
The centering quality of the tested sample was good. Field curvature is minimal.
Please note that the MTF results are not directly comparable across the different systems!
Below is a simplified summary of the formal findings. The chart shows line widths per picture height (LW/PH) which can be taken as a measure for sharpness. If you want to know more about the MTF50 figures you may check out the corresponding Imatest Explanations.
Chromatic Aberrations (CAs)
The Zeiss lens produces a low amount of lateral CA (color shadows at harsh contrast transitions) starting with an average CA pixel width of ~0.7px (borders) at f/1.8 increasing to ~1.2px at f/11 onward. This is usually not disturbing.
Bokeh
Outstanding sharpness is one thing but fast lenses are also about producing a shallow depth-of-field. For many users, a nice bokeh (rendition of the out-of-focus blur) is a major purchasing criterion.
The Sony lens continues to have a run here. Out-of-focus highlights are beautifully rendered with a very smooth inner disc and just very slight outlining. The circular shape remains intact at f/2.8. An edgy aperture shape starts to kick in at f/2.8.
Near the borders, the circular discs deteriorate to “cat eyes”. This is more pronounced than on the Batis lens but the inner zone is certainly smoother.
The general blur in the critical focus transition zone is pretty much perfect for a conventional lens. The background blur (to the left below) is marginally smoother than the foreground (right) here.
Bokeh Fringing
So-called bokeh fringing is an effect that occurs around the focus point (on the Z-axis). It’s visible as halos of different colours in out-of-focus areas – magenta (red + blue) in front of the focus point and green beyond.
The Sony FE 85mm f/1.8 may feature an ED element but it isn’t corrected for this type of fringing. The coloured halos are clearly visible at large aperture settings and traces remain at f/4.
If you traverse through the aperture range below, you will also observe that the focus remains static (thus no residual spherical aberrations).
The Competition
Those interested in the Sony FE 85mm f/1.8 will probably not really consider “the brick” – the Sony FE 85mm f/1.4 GM is shown to the left below. A more interesting question may be whether it’s worth to upgrade to the Zeiss Batis 85mm f/1.8 (center below). Honestly, the upgrade story is rather weak. The sharpness of both lenses is comparable and the Sony lens even has an edge in some of the other characteristics. The Zeiss lens features an image stabilizer which may be a plus depending on the camera body but then most Sony cameras feature in-body stabilization anyway. The Zeiss lens can have an edge at very close focusing distances though.
Visual comparison courtesy of camerasize.com.
Moderately fast (as opposed to insanely fast) 85mm or 100mm lenses are generally an easy choice unless something went terribly wrong during the design phase. Still, honours where honours are deserved - the Sony FE 85mm f/1.8 is an epic lens. It combines outstanding sharpness with a buttery bokeh which is a quite rare combination actually. Lenses that are pushing sharpness are usually not quite as smooth when it comes to the quality of the bokeh. Lateral CAs, as well as image distortions, are low. In terms of weaknesses, we'd list the bokeh fringing - albeit it isn't any worse than the competitors, a fairly high RAW vignetting at f/1.8 and a reduced quality at very close focusing distances (if that matters in this lens class).
The build quality of the lens is surprisingly high considering the fact that the lens is primarily targeting the consumer market. It's a tightly assembled, all-metal construction and it's weather-sealed, too. Manual focusing (by wire) works nicely and the auto-focusing speed is above average.
And to complete the nice story, all that is available at a very affordable price. Therefore, unless you really need that extra speed of a 85mm f/1.4 (and most don't really), we finish with … highly recommended!
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Optical Quality
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Build Quality
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Price / Performance