In this review we take an in-depth look at Sony’s FE 40mm F2.5 G lens, a compact and lightweight lens that is a great match for a compact E-mount camera like the Sony a7C.
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40mm is, for many people, a surprising focal length. It sits in-between the more common 35mm and 50mm. However, lenses in this range are not new. Pentax released a 43mm Limited back in 1997 (and still sells it today) and a 40mm in 2004. Prior to that, back in 1976, the company had relesed their first 40mm lens. Canon also released a 40mm in 2012, Voigtlander proposes an Ultron 40mm, Nikon proposes such a lens for the Z-mount, Leica has a Summicron, the list goes on.
Even on the E-mount, there are now a few proposals close to this focal length. In addition to Sony’s 40mm, Sigma offers a 45mm, as does Samyang.
Focal lengths around 40mm are, in fact, close to “normal” than 50mm. A normal focal length is one where the focal length is the same as the sensor’s diagonal; for a full frame sensor, this is exactly 43mm.
A normal focal length delivers a “natural” field of view, close to what the eyes see (in particular regarding perspective). 50mm is a good approximation, but 40-45mm is closer to the mark. These focal lengths are versatile and can be used for a variety of purposes.
The Sony 40mm is part of a trio of lenses, including a 24mm F2.8 and a 50mm F2.5, all with identical body sizes and almost identical weight. These lenses are intended for users looking for lightweight primes, but also for vloggers and users of gimbals, who will enjoy not having to recalibrate their equipment when changing lenses
In this in-depth review, we will take a look at all the technical and artistic parameters which help to define a lens. Read on to find out everything there is to know about the Sony FE 40mm F2.5 G!
|Lens Name||FE 40mm F2.5 G (Model SEL40F25G)|
|Optical formula||9 elements in 9 groups|
|Image circle||Full frame|
|Field of view diagonal||FF: 57°|
|Aperture blades||7, curved|
|Max magnification||0.2x (AF), expands to 0.23X (MF)|
|Minimum focus distance||280mm (AF), expands to 250mm (MF)|
|Filter thread diameter||49mm|
|Lens cap||Plastic, clip-on|
|Lens hood||Removable taper|
|Diameter x Length||68 x 45 mm (2.75 x 1.8 in)|
|Weight||173 g (6.2 oz)|
|Price (US MSRP)||$598|
Construction and Handling
In this section, we take a look at the physical characteristics of the Sony 40mm F2.5.
The front of the lens bears its name, minimum focus distance and filter diameter. The glass takes up a relatively small part of the total front surface.
The lens uses a small 49mm filter thread. This diameter is shared with its siblings the 24mm and 50mm. It makes it easy to use a single set of filters for several lenses.
The lens cap is plastic.
The Sony 40mm has a small body with a surprising amount of features and controls. It is also extremely light weight, despite being made of metal. It is identical to that of the Sony 24mm F2.8 G.
The bottom of the body, near the camera mount, the lens name and alignment dot. This dot protrudes for easier alignment.
Higher up is a section dense with features. In the center, bold lettering states for focal length (to distinguish it from the similar 24mm and 50mm).
To the left is the customizable focus hold button, as well as an AF/MF switch. Next to those is the G label, denoting (on paper) a higher level of quality than more consumer-oriented lenses.
On the opposite side is a switch to “de-click” the aperture ring, a feature desirable for videographers.
Next is the aperture ring. The ring is ribbed and easy to find, but narrow. There is an A (automatic) position to allow aperture control to be performed by the camera, and aperture values selectable in 1/3 steps increments.
In P and auto modes, the aperture ring does nothing. It serves in A and M modes. One thing to note is that the ring has no lock, and will often rotate with a little friction, for instance when inserting in a camera bag or just when mounting/unmounting the lens. Users will need to be careful not to move the ring unwillingly.
The last element, towards the front, is the focus ring. Wider than the aperture ring, is has an adequate, but by no means remarkable, level of friction.
The lens does not extend when focusing.
The lens is fully sealed against dust and moisture.
The Sony 40mm uses 7 curved aperture blades. As can be seen above, the curvature is moderate, and mostly manifests at wider apertures.
The lens mount is metal, and features a thin black o-ring to protect against water ingress.
The lens ships with a metal lens hood. It cannot be reversed for storage as it has a tapered shape, creating a window in front of the lens itself. While it increases the total size, it can be left on at all times since is features the same 49mm thread as the lens, and can hold the lens cap.
Mounted On Camera
The Sony 40mm looks right at home on the Sony A7C, for which it is an excellent match thanks to its small size.
Side by side
Here is the Sony 40mm next to Sony’s FE 28-60mm and the Tamron 20mm. It is an excellent match for the A7C’s kit lens; this similarity is probably intentional. It is dwarfed by the Tamron, which is often regarded as a compact lens.
The Sony 40mm F2.5 G uses no less han two linear motors to provide fast and precise AF. In particular, tracking is supposed to be enhanced.
In use, the Sony 40mm gives confidence in its focusing capabilities. The lens is almost completely silent.
Focusing feels very fast, responsive and reliable. The silent AF enhances this impression. The 40mm keeps up easily with subject tracking using AF-C. It supports every focusing mode available on the A7C.
There is a focus hold button, and an AF/MF switch on the lens. The switch is low on the lens barrel, making it harder to find at times. The focus ring is correctly dampened and shouldn’t move accidentally. It also gives adequate feedback to the user, not particularly pleasing, but accurate. The precision of the focus adjustments will be dictated by the speed of rotation of the focus ring. Sony did a good job even though focus-by-wire is not as direct as mechanical focusing.
We observed no occurrences of hunting during our tests, and rare misfocuses in low light.
AF speed was tested with the A7C. The subject was a black cross on a white background, about 1.5 meters in front of the camera. We used the central focus point. Three measurements were averaged for each data point.
For reference, 5 EV corresponds roughly to a small room lit with a 60 W bulb, a sunny day corresponds to 16 EV, and a moonlit night to -2 EV.
Even in low light, the Sony 40mm F2.5 G is fast and reliable. Around 0.9 seconds is a pretty good result. When light levels increase, AF becomes almost instant in our test, so quick it is hard to measure. These results, in line with those obtained with the Sony 24mm F2.8 G, are as good as we’ve seen.
Note that actual AF speed varies with the subject distance and conditions.
AF tracking, or continuous AF, is a hallmark of Sony cameras. As such, it is important to evaluate whether or not the Sony 40mm can keep up with fast movements of the subject.
In our experience, the lens performs very well in this regard, well within expectations. Once focus is locked, the camera keeps up with most subject movements. We rarely never encountered occurrences when the camera would lose its focus lock once achieved except at close distances.
The following animation shows a series of 30 images, and involves movement towards the photographer, followed by a rotation. The last 3 images are the only ones out of focus. The subject was still farther away than the minimum distance.
General Image Quality
Before diving into the technical aspects of this review, let’s have a look at the more subjective elements which can make or break an image.
Field of View
As discussed above, 40mm is close to a perfect normal, making this lens very versatile, a jack-of-all-trades.
It is suited for a variety of usages, from portraits to candids, landscapes and cityscapes. Distortion is easy to control on a 40mm lens.
40mm will also be well liked by vloggers who want a tighter angle than, say, 24mm, withwell-controlled distortion and a natural perspective. Portraits photographers will also enjoy the well-controlled aberrations; 40mm is useful as a portrait lens, especially in tight spaces where longer focal lengths are limiting.
The Sony 40mm F2.5 lacks any true close focusing capabilities. That is one limitation of this lens. It can still isolate subjects thanks to its moderately wide maximum aperture.
Color and Contrast
The images produced by the Sony 40mm F2.5 G are pleasing, with well-toned images, nicely saturated without going overboard. The rendering is fairly neutral, but with good tonal range.
Starbursts are not particularly impressive. Below F8 there is nothing to see and, even at that value, what rays we observe are diffuse. Even at F11 and beyond, the starbursts are never particularly remarkable. Users should not use this lens with the intent to create starbursts.
Metering and Exposure
Exposure was mostly consistent and reliable. We observed some rare occurrences of underexposure, but these were not frequent.
Sharpness, or a lens’s ability to resolve small details, is far from the only important characteristic of a lens, but it is probably the one which many users look at first. Soft images distract the viewer and the sharpest point in an image draws the eye of the viewer.
There are several ways to measure resolution. Some are quantitative, such as the number of lines per millimeter that can be resolved, while others are comparative, such as using a standardized scene to pit lenses against one another. We will use the latter, and supplement it with real-life samples.
To evaluate sharpness, we use a standard test chart that can be used to compare lenses to one another. We place the camera and lenses at a distance of 100x the focal length, so that the chart occupies the same area on all test images. This results in distances of 4 m in the present case. The chart is positioned successively in the center, on the edge and corner off the frame, testing all apertures each time. Focus is repeated for each position to avoid field curvature contributions.
This test will not show how good a lens can be. Quite the contrary, it is a stress test to illustrate the limits of a lens’s capabilities.
Resolution is of course sensor-relevant. For this test we use the A7C camera’s 24 MP sensor.
Test results at 40mm
The following images illustrate the results at all apertures at 40mm.
These results illustrate the Sony 40mm’s capabilities and limitations. In general, they are in line with our findings with the company’s 24mm.
In the center, the results are already excellent wide open, and improve marginally F5.6 and F8. F16 remains usable, while F22 can serve in a pinch, but shows decreased resolution.
Edges are never as good as the center. The difference is small at F8 and F11, but wide open it is significant, and will be noticeable.
Corners show poor sharpness. F11 shows a peak in resolution, where the difference with the edges and center is less prominent. Wide open and until F5.6, the corners are unacceptably soft.
These results are good news for photographers who wish to isolate their subject from the background, but bad news for anyone else. Portraiture won’t be affected all that much, but anyone looking for a wide field of view with edge-to-edge sharpness simply won’t find it with this lens.
In the plus side, the discrepancies between the edges and center will not always materialize, in particular because the “center” section expands to a large part of the frame.
Excellent center sharpness, poor corners and no more than adequate edges. Users expecting tack-sharp results across the whole frame will not be satisfied.
Vignetting, or the darkening of corners at wider apertures, is both a defect and a feature, as it can be used creatively to put emphasis on subjects closer to the center, create a mood or a vintage look. It can also be corrected automatically by modern cameras so is less of a problem than in the past. That is only true for lenses with electronic contacts, including the Sony 40mm.
The following chart illustrates the vignetting of the lens for full frame when left uncorrected.
The Sony 40mm’s designers visibly decided to rely on automated corrections for vignetting. This is not surprising but certainly something to be aware of. Wide open, vignetting is strong and will be apparent. Closing down brings the effect lower, but still around1 EV, remaining noticeable. We recommend using automatic correction profiles to avoid the effect.
Note that, when using JPEGs, the camera does not allow disabling of the automatic corrections. It seems the designers were aware of the strong vignetting created by the Sony 40mm.
The images below show the lens’s vignetting at varying apertures.
|Full frame 40mm|
Bokeh is a Japanese term describing the quality of the background blur. It does not relate to the depth of field but to the areas in the image that are beyond the range that is expected to be in focus.
Bokeh is highly subjective. In general, a smooth bokeh with blurred shapes and contours is generally perceived as being of a higher quality. A shallow depth of field does not always equate a more pleasing bokeh.
To evaluate the characteristics of the background blur, we took pictures at varying apertures, using a scene with a lot of detail and bright highlights. The following images show the results.
Thanks to the F2.5 maximum aperture, depth of field can be made shallow. Subject isolation is easy and transitions between in-focus and out-of-focus are gradual and pleasing. In this the Sony 40mm does superbly. Even at smaller apertures, transitions remain smooth and subject isolation is present. Even the busier textures are well rendered (see the leaves between the two leftmost flowers’ stems).
Highlights are circular between F2.5 and F4. There is some cat’s eye effect on a significant part of the frame, but these are not disturbing. The background allows a pleasing 3D “pop”. This subjective rendering is better than usual.
Closing the aperture beyond F4 gives more shape to the highlights. They do not remain circular despite the curved aperture blades. Despite this, the background blur remains quite smooth and isolation is still present.
Bokeh rendering is one of this lens’ stronger elements.
Flare and Ghosting
Flare is a decrease in contrast caused by reflections on internal lens elements. Ghosting is the appearance of orb-shaped artifacts in an image containing a light source, caused by the same internal reflections. High-quality coatings reduce the importance of flare and ghosting in an image.
We test flare and ghosting by taking pictures of a bright light source positioned at the center and on an edge of the frame, at varying apertures.
Test results at 40mm
There are two lines showing in the center at F4 and F5.6. Those were caused by a plane and shouldn’t be considered.
In the center, at wider apertures flare is well controlled. There are some ghosts, but they are not very apparent. At medium apertures, the ghost become more apparent, becoming more numerous and more visible as the aperture closes. Thankfully, there is no hint of flare or decrease in contrast.
With the light in the corner, results are impressive, and much better than expected. There are some ghosts close to the light source, but almost none elsewhere. We typically observe a row of ghosts on the diagonal with this kind of test, and none are visible here. Stellar results.
Chromatic aberration (CA) occurs because different colours do not always have the same focal point. With modern lenses designs, which are better corrected than vintage designs, this is more likely to occur in out-of-focus areas. CA effects are more visible near fast transitions from bright to dark areas.
Most modern cameras have built-in tools to remove CA. Digital manipulations can have an impact on other aspects of an image, thus it is useful to know how a lens performs when those automatic corrections are disabled.
Our test sets up the camera at 45° and focuses on the center of the frame, with targets at the center, top and bottom. Images are captured at varying apertures.
The center is devoid of any chromatic aberration effects. The same can be said for the top section. However, the bottom shows some CA below F5.6. It is not bothersome but still present. Automatic in-camera corrections will take care of it.
There were no occurrences of purple fringing in our tests with the Sony 40mm.
Distortion refers to a lens’s ability to represent straight lines as straight lines… Wide angle lenses frequently generate barrel distortion, while longer focal lengths are more likely to cause pincushion distortion.
The Sony 40mm is a normal lens. As such, we expect excellent control over distortion.
We use a standard test pattern of straight lines and test at 40mm.
The Sony 40mm shows almost perfect control over distortion. We measured 0.1% of barrel distortion, which will have no impact on images whatsoever.
Here is a gallery of samples images captured with the Sony 40mm. You can click on individual images for a larger view.
With this review, we continue our exploration of Sony’s trio of compact, metal and weather-resistant primes.
The 40mm F2.5 surprised many people, in part because many users are not familiar with this focal length. Also, as a lens which will, for some, be compared with the many 50mm options on the market, the 40mm’s moderately fast aperture of F2.5 won’t offer a compelling advantage over walkaround zooms such as Tamron’s 28-75mm F2.8 and equivalents from Sigma and Sony.
The 40mm pales when compared with the big guns from Sony. Many people expect primes to have large apertures, and the company’s GM lenses happily comply. Their size and price are also large, however. Compared to that, the 40mm F2.5 G is almost the same size as the company’s retractable kit zoom, and weights a paltry 173g (compare that to the 50mm F1.2’s 778g!).
Sony touts the trio of G primes as designed for gimbals, since they can be swapped without recalibrating the gimbal. They also make a lot of sense as a lightweight travel kit. Carrying the 28-60mm kit lens with a few of those primes will weight less than one single fast-aperture prime, and take up much less space. Such a strategy has the zoom serve as a general-purpose lens, with the primes filling in for lower light or shallow DOF applications.
Build quality on the Sony is excellent. The metal housing feels utilitarian instead of jewel-like, and gives a sense of ruggedness. The small size of the lens must be emphasized.
There are a lot of buttons and switches for such a small lens. They are welcome and useful. The AF / MF switch is sitting a bit low for easy access. One thing to mention is that the aperture ring does not lock into place and often moves when handling the lens.
Optical performances are a mixed bag, with some very good points but a few important problems.
Center sharpness is excellent, even wide open. Edges are not as good except at medium apertures, but the true problem is that corners are never good at all. This might or might not be a problem, but users should dive in knowing this limitation.
Vignetting is also disappointing, being present in significant amount at all apertures. It can be automatically corrected, but is still a weak point of the optical design.
Chromatic aberration is not completely absent, but very well controlled.
Distortion control is near perfect, reaching no more than 0.1%.
Bokeh and out-of-focus rendering is extremely pleasing, with gradual transitions and well-rounded highlights, particularly at wider apertures. There is some cat’s-eye effect, but it is not distracting.
Flare and ghosting are a strong point. Particularly with light sources near the corners, the lens does admirably.
Starbursts are nothing special even at small apertures, the rays are diffuse and diverging.
Autofocus is stellar. Silent, very fast (hard to measure in good light), dependable, it certainly is a perk of this lens.
In summary, the Sony 40mm F2.5 G is hindered by the (easy to correct) vignetting, and more importantly by the weak corner sharpness. Whether or not that is a problem will depend on the application. If edge-to-edge sharpness is important, then the 40mm isn’t the best choice. If the intended use implies centered subjects and narrow DOF, the combination of center sharpness and beautiful bokeh will be beneficial (and the vignetting can be used beneficially).
Like its siblings, the Sony 40mm proposes a very compact body, light weight (especially given the metal housing), blazing fast AF, very good center sharpness, good control of flare. 40mm is a less common focal length that often grows on users, many of whom will get back to 50mm’s narrower FOV grudgingly.
There certainly is a growing market for lenses close to 40mm, with proposals from Samyang and Sigma among others to compete with Sony’s product. The Sony is more expensive, but is the only one to propose full weather sealing. For anyone wishing to travel light, this might be reason enough to pick the Sony lens.
- Light and extremely compact
- Weather resistant
- Several buttons and switches on the lens
- Excellent center sharpness at nearly all apertures
- Blazing fast, silent AF
- Low distortion
- Good control over flare and ghosting
- Great bokeh rendering
- Strong vignetting when left uncorrected
- Underwhelming sharpness on edges, poor in corners
- Aperture ring does not lock in place
- Expensive when compared to the competition
Before You Go
Do you already own this lens? Are you curious about it? If you do, we’d love to hear your thoughts in the comments below.