As its focal length is in the middle of Sony’s recently introduced trio of compact primes (24, 40 and 50mm), the FE 40mm f/2.5 G could easily be overlooked, but it’s worthy of serious consideration. It can also arguably do the job of the others if you’re prepared to step forwards or back to alter the framing.
To summarise the Sony FE 40mm f/2.5 G, it’s small, light and razer-sharp, everything you want from a take-everywhere lens.
Compact and lightweight
Maximum aperture 'just' f/2.5
What is the Sony FE 40mm F2.5 G?
The Sony FE 40mm F2.5 G was announced at the same time as the Sony FE 24mm F2.8 G and FE 50mm f2.5 G and is a very similar size and weight to those lenses. It’s a compact prime lens with an angle of view very close to that of the human eye.
As it’s a full-frame lens with the Sony E-mount, the FE 40mm F2.5 G is designed for use on Sony’s full-frame mirrorless cameras such as the Sony A7 III and A7R IV or Sony A1. A 40mm focal length is also very popular for video, which means it could appeal to videographers using the Sony A7S III.
Furthermore, because it’s the same size a very similar and weight to the FE 24mm F2.8 G and FE 50mm f2.5 G, swapping between the three optics causes minimal disruption when shooting with the camera on a gimbal such as the Zhiyun Weebill 2 or Weebill-S.
Diameter x length (extension from lens mount): 68 x 45mm / 2-3/4 x 1-13/16 inches
Sony makes the FE 40mm F2.5 G’s barrel and removable hood from aluminium and there are seals to keep out dust and raindrops.
Optically, the lens is constructed from 9 elements arranged in 9 groups and there are 3 aspherical elements to help deliver high resolution across the entire frame.
Like the FE 24mm F2.8 G and FE 50mm f2.5 G, the Sony FE 40mm F2.5 G has two linear focusing motors for fast, quiet focusing. When the autofocus (AF) system is engaged, the FE 40mm F2.5 G has a closest focusing distance of 28cm or 0.92ft, at which the magnification is 0.2x. However, switching to manual focus enables the focusing distance to be reduced to 25cm or 0.82ft while the magnification rises to 0.23x – almost a quarter of lifesize.
Adopting the same design as its 24mm and 50mm siblings, the the FE 40mm F2.5 G has an aperture ring with settings running from f/2.5 to f/22 in 1/3EV steps. There’s also an ‘A’ setting which enables the aperture to be set using the camera’s control dial. This ring has click stops but it can be ‘de-clicked’ using a switch on the barrel.
In addition, there’s a customisable Focus Hold button and a switch to set the lens to automatic or manual focusing.
Build and handling
With a diameter of 68mm or 2-3/4-inches and a length of 55mm or 1-13/16 inches from the lens mount, the Sony FE 40mm F2.5 G is exactly the same size as the FE 24mm F2.8 G and 50mm F2.5 G – although the 24mm lens uses a different type of lens hood. And at 173g or 6.2oz in weight, it’s just 11g (0.4oz) heavier than the 24mm lens and 1g lighter than the 50mm lens. Those differences are not noticeable when the lenses are mounted on a camera.
When the Sony FE 40mm F2.5 G is mounted on the Sony A7R IV, the overall kit weighs less than 840g, including the battery and a memory card, making a nicely portable full-frame set-up.
The lens is also nicely sized and balanced on Sony’s current full-frame mirrorless cameras. As the manual focus ring is at the far end of the lens, it’s easy to locate and it only takes a little pressure from your left index finger to rotate it.
As the FE 40mm F2.5 G has linear response manual focusing, it reacts quickly to rotation of the focus ring and it’s precise. However, the focusing is by wire which means there are no physical end stops to the focus ring’s rotation. There’s also no distance scale on the lens barrel, but a scale pops up in the viewfinder or on the screen as soon as the ring moves. This shows a numerical value for the focus distance.
I’m a fan of aperture rings on lenses, so I’m pleased to see one on the FE 40mm F2.5 G. It’s also good to see that there’s a switch that gives you the option of using it with or without click-stops. The click switch sits close to the lens mount, just where my left index finger rests, which is convenient if you like to swap between the two settings on a frequent basis for some reason.
When it’s de-clicked, the aperture ring moves smoothly, but when the clicks are engaged, there’s nice feedback as the ring turns.
Just above the AF/MF switch on the left of the lens barrel, there’s a customisable button. In continuous focusing mode, this is often used for pausing the focus (focus hold), but Sony A7-series cameras enable one of a long list of features to be assigned to it. I find it handy to use it to toggle between the Eye AF subject options.
I used the Sony FE 40mm F2.5 G on the Sony A7R IV, which, with 61-million effective pixels, is the highest resolution full-frame camera currently available. That means that the lens’s resolving power had every chance to show itself, and I’m very impressed by the amount of sharp detail visible at the centre of its images.
Even at maximum aperture, f/2.5, there’s a very high level of sharpness and nice micro contrast. However, closing to f/2.8 ups the game slightly and at f/4 and f/5.6, the sharpness is stunning – it’s hard to imagine that there can be more detail in an image.
When images are sized to fill a 27-inch screen, there’s a slight fall-off in sharpness apparent at f/2.5 but it’s not problematic. Closing to f/2.8 improves the situation and by f/4 the fine details are crystal-clear.
Sharpness levels stay very high up to around f/11 and beyond, but by f/16 there’s a suggestion of the impact of diffraction and if you examine images at 100%, you’ll see the corners soften again fractionally. Diffraction means that the results at f/22 suffer in comparison with those captured at mid-range apertures. They’re not bad, but it’s worth sticking to f/16 or wider if you can.
Out of focus areas generally look good from the Sony FE 40mm F2.5 G, they’re pleasantly smooth and rounded. However, scrutinising the ‘bokeh balls’ created by pinpoint highlights reveals that some have a hint of bokeh chromatic aberration and concentric circles (onion skin effect) within. Also, the highlights towards the edges of the frame take on a ‘cat’s eye’ shape.
If the in-camera or post-capture correction profiles aren’t applied, very slight barrel distortion is visible in images with lots of straight lines. There’s also a little vignetting at f/2.5, but it’s well within an acceptable range and using the correction profile or closing to f/4 eliminates it if you find it troublesome.
Even with the correction profiles applied, I found a few examples of chromatic aberration causing purple fringing along backlit edges. However, it’s not a major problem and it’s dealt with in a matter of seconds using Adobe Camera Raw’s ‘Defringe’ tool.
Sony supplies a conical or inverted type lens hood with the FE 40mm F/2.5 G and this does a great job of keeping flare at bay. If the hood if removed and the lens is angled so light skims across its surface or the sun is towards the edge of the frame you can force the issue and introduce a little flare, but that’s inevitable and its controlled well.
As you’d expect, the Sony FE 40mm F2.5 G is fully compatible with Sony’s latest autofocus systems, including Eye AF. It gets subjects sharp very quickly and silently. However, adjusting the focus from the closest focus point to the furthest, or vice-versa results in a change in the framing, which could be an issue for some videographers or photographers looking to focus stack.
As a wide-angle fan, I was immediately drawn most to the FE 24mm f/2.8 G in Sony’s new trio of prime lenses, and while that is a great lens, the FE 40mm f/2.5 G is arguably more versatile. It’s also optically very good, delivering super-sharp images without any significant flaws.
The Sony FE 40mm f/2.5 G is also very compact and light, making it a great partner for a Sony A7 III or any of Sony’s other full-frame mirrorless cameras. It’s a great choice for environmental portraiture, street photography and reportage or even landscapes.
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