The Panasonic Lumix S 20mm F2.5 is a small, affordable wideangle prime that’s designed for the firm’s full-frame mirrorless cameras. In particular, it’s aimed at users of the compact, rangefinder-styled Lumix S9, which is popular for video and vlogging. And this lens’s focal length means it could be very useful for both those activities, in effect turning the S9 into an upmarket version of the DJI Osmo Pocket 4.

　　Panasonic Lumix S 20mm F2.5 at a glance: £429 62mm filter thread 18cm minimum focus 69.4mm diameter x 40.9mm length, 142g L-mount I’m neither a videographer nor a vlogger, but I am a photographer who’s rather fond of the 20mm focal length. It gives a usefully wider view than most standard zooms, without too much of the ultra-wideangle distortion and edge stretching that can become problematic even on 16-35mm zooms. I could see this lens being popular among photographers shooting such things as buildings and landscapes, who’d like something wider than a typical 24-70mm or 24-105mm standard zoom, but in a form that’s small and easy to carry for travel.

　　As an L-mount lens, this doesn’t just work with Lumix cameras, on but Leica and Sigma’s mirrorless bodies, too. It could be a particularly nice match for Sigma’s small fp, fp L and BF models, for example. It’s considerably smaller than its most obvious alternative, the Sigma 20mm F2 DG DN, and more affordable too, at just £429. Of course, the trade-off is the smaller aperture, but f/2.5 should still be useful for shooting indoors and in low light. So how does the lens perform?

　　Features Despite the lens’s compact size, Panasonic really hasn’t skimped on the optics. The design employs 11 elements in 9 groups, including 3 aspherical elements to maintain cross-frame sharpness and 3 extra-low dispersion (ED) elements to suppress colour fringing from chromatic aberration. In comparison, the firm’s similarly-priced 40mm F2 comprises 7 elements in 6 groups in the exact same size barrel.

　　You get a relatively simple aperture diaphragm with 7 curved blades, which provides settings down to f/22. The minimum focus distance is 18cm, equating to a working distance of about 12cm from the lens to the subject. That in turn represents a subject width of around 19cm, so this isn’t a particularly good choice for close-ups.

　　As befits a wideangle prime, the lens is constructed for use in the great outdoors. It features dust- and splash-resistant construction, with seals around the mount and all the controls. This is complemented by a fluorine coating on the front glass to repel fingerprints and raindrops.

　　There’s a 62mm thread at the front for attaching filters, which is shared with both the 40mm F2 and the ultra-compact 18-40mm F4.5-6.3 zoom. But like those lenses, one thing you don’t get is any provision for using a hood, with Panasonic instead preferring to keep the design as slim as possible.

　　I’m not a fan of this at all, as I value the protection a hood provides the front glass against knocks and scratches. With the 40mm, you can just use a 62mm screw-in hood. But with the 20mm, you’d need to find a very shallow one, that’s unlikely to work very effectively.

　　Build and handling As full-frame lenses go, this is a very small and lightweight design. It’s 69.4mm in diameter, 40.9mm in length, and 142g. That makes for a particularly portable combination with the Lumix S9, but I also found it to be a very agreeable partner for the SLR-shaped Lumix S5IIX. It adds barely any weight or bulk to the body at all.

　　In another sign that the lens is primarily aimed at S9 users, the lens has both an AF/MF switch, and a Lens Fn button on the barrel. The former isn’t really necessary with Panasonic’s SLR-shaped cameras, as they all have a focus-mode switch on the body. Indeed, having the same control on the camera and lens can be a recipe for confusion, if one is set to AF and the other to MF.

　　By default, the Lens Fn button is set to Focus Stop, but it can be reassigned to a range of other settings via the camera’s menu. Likewise, you can reassign the focus ring to control a different function when the camera is set to autofocus, such as ISO or exposure compensation.

　　Personally, though, I preferred not to do this, as the focus ring only rotates smoothly without tactile feedback, which means it’s nowhere near as nice to use for such settings as a clicked dial. I found it quite easy to nudge accidentally, too.

　　In manual focus, you can set the ring to either linear or non-linear operation, and choose which direction of travel you prefer. In linear mode, you can choose the angle required to get from infinity to minimum focus, from 90° to 360°. Personally, I set it to linear with a 90° throw, which worked well for my needs.

　　Autofocus When it comes to the autofocus performance, there’s absolutely nothing to complain about. Focusing is fast, silent, and consistently accurate. There’s no hint of focus breathing, either.

　　The lens works perfectly in conjunction with subject detection, too, tracking and holding focus on faces as they move around the frame and closer or further away. That’s great for hand-held arms-length vlogging; set the camera to C-AF and face detection, and it works pretty much flawlessly. All-in-all, it’s an exemplary showing.

　　Performance Optically, the Lumix S 20mm F2.5 is a solid performer. I tested it on a couple of Panasonic’s 24MP Lumix S cameras, the S9 and S5IIX, and it delivered nice, sharp images with no nasty optical defects.

　　Detail resolution is very impressive in the centre of the frame, even at f/2.5. Unsurprisingly, if you examine your images close-up onscreen, there’s a little blurring and loss of contrast visible towards the corners of the frame. This improves quickly as you stop down, although the corners and edges never quite match the centre for outright sharpness.

　　Even so, at the normal working apertures of around f/8-f/16 that I’d use for full-frame, images look pretty crisp and detailed from corner to corner. Stop all the way down to f/22 and you’ll see some blurring due to diffraction, but that may be an acceptable compromise when you need extended depth-of-field.

　　Overall, looking back though all the images I shot with the lens, the most significant source of blur was a lack of depth-of-field at large apertures, which outweighed any optical aberrations. It can be tempting with such a wide lens to assume everything will end up in focus regardless, but that’s not necessarily the case. So you still need to be careful with selecting your focus point when using large apertures in low light (which probably shouldnt come as a surprise).

　　Vignetting compensation is turned on by default on Panasonic’s L-mount cameras, so you won’t see much in the way of corner darkening at large apertures. If you choose to disable compensation, you’ll find that corner darkening is very obvious at f/2.5, but with a gradual fall-off profile that means it’s not unattractive. Stop down to f/5.6, and it’s pretty much gone.  

　　In normal use, straight lines are rendered correctly without any distortion. If you choose to disable profiled lens corrections in raw processing, you can see that there’s some significant underlying barrel distortion. But as this is automatically corrected in software, both in-camera and in raw processing, most users will never even see it. 

　　In a similar fashion, you won’t see much in the way of colour fringing due to chromatic aberration, as it’s automatically fixed by the camera’s processing. Just occasionally, though, I saw a tiny amount of residual green/magenta fringing when processing raw files. But clicking ‘Remove chromatic aberration’ in Adobe Camera Raw put an end to that.

　　About the only aspect of the lens’s performance that I found disappointing was how it dealt with shooting directly into the light, with the sun in the frame. Rather than giving nice, clean sunstars, it smears rather dramatically instead. That could be a cause for concern for landscape photographers.

　　Panasonic Lumix S 20mm F2.5: Our Verdict With the Lumix S 20mm F2.5, Panasonic has made a fine little wideangle prime that, on the whole, performs well. It’s compact and easy to carry all day, weather-resistant for outdoor use, and delivers decently sharp images given the price. Its autofocus is fast, silent and accurate too. Size-wise it’s a great complement to the Lumix S9, on which it should work particularly well for video and vlogging.

　　As a stills photographer, I’m a fan of using small 20mm lenses to complement 24mm standard zooms without the bulk (and expense) of ultra-wide zooms. Here, the 20mm F2.5 does a very creditable job, although landscape photographers might be unhappy with its inelegant sunstars. Personally, I also wish it could accept a hood to help protect the front element from knocks and rain – but equally, other photographers are entirely happy never using a hood.

　　One complication, of course, is that many Panasonic users will already own the Lumix S 20-60mm F3.5-6.3, as it’s long been the kit zoom for the Lumix S5 series. If that’s your primary lens, I’m not sure there’s much reason to buy a 20mm prime. It’s perhaps easier to make a case for it over the S9’s 18-40mm F4.5-5.6, though, on the basis of its larger aperture. That caveat aside, though, for L-mount users seeking a lightweight wideangle prime, the Lumix S 20mm F2.5 is well worth a look.

　　Panasonic Lumix S 20mm F2.5 full specifications Scroll to see more →

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