Intro

The Sigma 18-50mm f2.8 DC DN is a general purpose zoom with a constant fast aperture for mirrorless cameras sporting cropped APSC sensors.

Announced in October 2021 at a very reasonable price of $599 or 429 pounds, it’s actually Sigma’s first zoom designed for mirrorless cameras with cropped APSC sensors. At the time I made this review it was only available in Sony-e and Leica L mounts, but I’m sure I’m not the only one who’d also love to see Fujifilm X and especially Canon EF-M flavours. However many versions Sigma ends up making though, the premise remains the same: a general-purpose lens that’s a step-up in aperture and sharpness from often disappointing kit zooms. In my video review below, I’ll compare the e-mount version of the lens against Sony’s ubiquitous 16-50mm f3.5-5.6 kit zoom, but if you prefer to read the written highlights, keep scrolling!

Sigma wasn’t the first with this idea though. In August 2019, Sony launched the E 16-55mm f2.8 G, sharing the same aperture as the new Sigma but with a fractionally broader range. However the Sony’s larger, heavier and at $1399, much more expensive.

Meanwhile at the end of 2020, Tamron launched the 17-70mm f2.8, again for Sony e-mount with the same aperture, but this time extending the range further, especially at the long-end. Inevitably this also makes it heavier and longer than the Sigma, but at $799 it’s priced keenly for its range especially as it’s the only one of these three 2.8 zooms to also include optical stabilisation.

I hope to make some direct comparisons between the Sigma, Tamron and Sony 2.8 zooms in the future, but for this video I’m going to concentrate on the performance of the new Sigma versus the Sony 16-50mm 3.5-5.6 as it’s one of the most widespread kit lenses out there. Just before I start, this video is sponsored by none other than you dear viewer. You’re clearly a person of great taste so thanks for watching and if you’re not already subscribed please consider it so you don’t miss any of my future reviews! For more information on, er, you, check the link below, oh no, I’ll just get on with it.

Ok, so here’s the Sigma 18-50 2.8 mounted on my own Sony A6400. It may have a shorter range than the Sony 2.8 and especially the Tamron, but at 60x76mm it’s comfortably more compact than either model, and at just 288g, roughly half their weight too. In terms of controls, there’s just two: a fairly narrow manual focusing ring with ribbing that’s flush to the barrel making it a little awkward to turn at times, and a wider zoom ring that extends the barrel by about 24mm. Like the other two premium options, Sigma supplies the lens with a plastic hood, although the 55mm filter thread is narrower than the 67mm on the Sony and Tamron.

But while the Sigma becomes the most compact of the three 2.8 zooms, none can match the tiny 16-50 3.5-5.6 from Sony, supplied over the years with so many A5000 and A6000 cameras. Whatever criticisms you can level against this lens, being too big is not one of them. It weighs-in at a barely noticeable 118g and employs a collapsing barrel which starts off at just 65x30mm, before extending when powered-up. The single control ring adjusts either the zoom or manual focus, while an additional lever provides an alternative zoom control. Note the zoom is motorised on this lens.

The Sigma is weather-sealed at the mount, albeit not throughout the entire barrel, but this is an upgrade over the Sony 16-50 kit zoom which has no sealing and feels quite rattly in comparison.

To test the focusing I mounted each lens on my A6400 and recorded the view in both Single AFS and Continuous AFC modes. Starting with the Sigma 18-50 at 50mm f2.8 in AFS, the focusing is very swift with only the usual minor contrast wobble to confirm and it’s effectively silent too. And next here’s the Continuous AFC version which uses phase-detect autofocus and avoids the wobble; it’s a little faster too.

For comparison, here’s the budget Sony 16-50 kit zoom at 50mm, although its maximum aperture is two stops slower at this point at f5.6. Still, the result with Single AFS is quick and again it’s effectively silent. And for reference, here’s the same kit zoom in Continuous AFC mode where again it’s quicker still. The kit zoom certainly has its faults, but none in the autofocus department.

Alright, now it’s time to check out some photos, starting with the range of the Sigma 18-50mm, mounted on my Sony A6400 at 18mm where it delivers a 27mm equivalent field of view. Compare that to the Sony 16-50 at 16mm and you can see the little kit zoom clearly capturing a slightly wider field of view, so that’s the first question you’ll need to ask yourself: is the Sigma wide enough? Here it is again at 18mm, and of course I’d prefer it to start at 16mm, but as you’ll see the quality is superior to the kit zoom and the aperture brighter too, so you’ll need to weigh-up the pros and cons.

And now for the Sigma 18-50 at 50mm where it delivers a 75mm equivalent field of view that’s great for portraits as I’ll show you in a moment. In my tests the Sony 16-50 matched this view at the long-end as its specs suggest.

Before comparing their quality across the frame I wanted to make a quick note about distortion and lens corrections. When zoomed to the widest 18mm end, the Sigma 18-50, like many wide lenses, exhibits quite strong barrel distortion. It’s particularly noticeable when shooting face-onto shapes you know to be square in real-life like brick walls or buildings. Luckily the 18-50 responds well to lens corrections, so here’s the same shot taken with Distortion set to Auto in the Sony menus and you can see it’s much better, albeit with a mild crop as a result. I found the distortion quickly reduced as the focal length increased and wasn’t an issue for mid to longer lengths. But you will notice it at the wide end unless you have lens corrections enabled.

Ok to compare their quality I’ve angled my landscape view so that details run into the corners, starting here with the Sigma 18-50 at 18mm f2.8. Taking a close look at the middle shows good detail as you’d expect, and there’s little benefit to closing the aperture other than a minor boost in contrast. Heading out into the corner, still at f2.8, you’ll see the Sigma maintaining the sharpness, and again there’s only small benefits to closing the aperture, like a mild boost in contrast and a small reduction in fringing. I’d be happy shooting wide-open where necessary or desired for a shallow depth of field, but for the maximum quality across the frame, try f5.6 to f8.

Ok now for a side-by side with the Sigma at 18mm f2.8 on the left and the Sony 16-50mm kit zoom at 16mm f3.5 on the right. Looking at the centre of each image shows a similar result, but moving to the far corner, where they show different sections of the pier due to their different focal lengths, reveals a dramatic difference in sharpness. The Sony 16-50 kit zoom is notoriously bad at 16mm, at least in my tests with multiple copies, and this is my best one. Part of the issue is lack of field flatness and in this example I had both lenses focused in the middle of the frame, but even if I switch the Sony image on the right for one focused in the corner, it still falls below the Sigma. The Sony lens can improve in the corners, but you’ll need to close it to around f8.

Next for the Sigma roughly halfway through its range at 35mm for standard coverage, again wide-open at f2.8 where the story remains the same as before. It’s nice and sharp in the middle with only the slightest hint of fringing in areas of high contrast. Close it by a stop and you’ll eliminate that along with gaining a small boost in contrast, but again I’d be pretty happy with the result wide-open if I had to shoot at 2.8. Moving out into the corner continues the story of decent performance with the aperture wide-open. Again there’s little to be gained from closing the aperture here other than to lift what was already fairly mild vignetting.

Returning to the middle of the frame with the Sigma on the left at 2.8 and the Sony on the right at f5 which is the maximum aperture for that lens when set to around 35mm, and the results look pretty similar. Head into the far corner though and you’ll see the Sigma on the left looking noticeably sharper, and remember this is when its aperture is almost two stops brighter too. The Sony kit zoom can match this sharpness, but you’ll need to close it to around f8, by which point it’s three stops slower.

And finally for the Sigma 18-50 at 50mm f2.8, and taking a closer look in the middle shows no problem at all with sharpness with plenty of detail and high contrast from the get-go; again closing the aperture can fractionally improve the overall crispness, but I’d be happy shooting wide open if I needed to.

Moving into the far corner at 50mm f2.8 and you’ll see the Sigma maintains the sharpness across the frame, and stopping-down only results in a mild boost in contrast. As before the best results are at around f5.6 to f8, but it looks great at f2.8.

So for my final distant comparison here’s the Sigma on the left and the Sony on the right, both at 50mm and their maximum apertures of f2.8 and f5.6, so two stops apart. Comparing their results in the middle again shows the Sony on the right can keep-up in this part of the frame, but in the corner there’s a noticeable difference with the Sigma visibly out-performing the Sony kit zoom. Again you’d need to close the Sony down to f8 or smaller to match the Sigma when it’s operating over three stops faster. So a great result for the Sigma 18-50 2.8 for distant subjects.

Ok now for portraits, so here’s one taken with the Sigma 18-50 at 50mm f2.8 where you can enjoy some blurring in thee background – not as much as a faster prime of course, but more than a typical kit zoom. Looking closer at my eyes shows a good amount of crisp detail and you’ll also see the background blur is reasonably smooth and unfussy.

Pop the Sigma on the left with the Sony on the right, both at 50mm, and you’ll immediately see the difference between a lens that can open to f2.8 on the left versus one that’s limited to f5.6 on the right. To be fair, the Sony’s actually fairly sharp on the focused areas, but there’s unsurprisingly little blurring behind me to speak of. Just out of interest, I’ll switch the Sigma image on the left for one with its aperture closed to f5.6 to match the Sony on the right to compare their rendering styles, and in this instance I’d say the Sony is a fraction less busy, but as you’ll see in the next test the Sigma takes a lead.

Ok so now for the rendering of bokeh balls at close range, again starting with the Sigma 18-50mm at 50mm f2.8 and focused close to its minimum distance. At the maximum f2.8 aperture, the Sigma lens is delivering fairly large bokeh balls with a little outlining and some mild textures within – not surprising for a zoom of this size, but still a step-up from budget models. And now closed to f4, then f5.6 and finally to f8.

Now here’s the Sigma on the left and the Sony on the right, both from the same distance, both set to 50mm and their maximum apertures of f2.8 and f5.6 respectively. Here the two stop benefit of the Sigma on the left is obvious with a much shallower depth of field, but the rendering is much more attractive too with the blobs from the Sony on the right suffering from much more obvious onion-ring textures within. So as expected, the Sigma offers a step-up in rendering quality over the basic Sony kit zoom.

At the other end of the scale, here’s what happens when the Sigma is set to 18mm f22 for that sunstar effect.

And finally a macro test with the Sigma at 50mm f2.8 and focused as close as it could to the ruler where it’s reproducing a subject size of 85mm across the frame. And now for the Sigma at the top and the Sony at the bottom, the latter at 50mm f5.6 and again as close as it would focus, where it reproduces 93mm across the frame.

Moving onto video, the Sigma 18-50 provides a useful general-purpose range with greater opportunities for blurring than a typical kit zoom. 27mm equivalent is too long for handheld vlogging, but zoom the lens to 50mm as I have here and it’s great for presenting tripod-based pieces to camera at various distances. Opened to f2.8 you’ll enjoy some nice blurring and the lens kept me focused easily on the A6400. For comparison, here’s the Sony 16-50 kit zoom at 50mm f5.6 where it too can keep me in focus, but you’ll see much less opportunity for blurring in the background.

Here’s another example of focus-pulling for video, starting with the Sigma 18-50 at 50mm f2.8 and now for comparison the Sony 16-50 at 50mm f5.6 where again there’s much less blurring possible.

As for focus breathing, here’s the Sigma 18-50 at 18mm f22 where you’ll notice barely any impact on magnification as I focus from infinity to the closest distance and back again. And now at 50mm f22, again focusing from infinity to the nearest and back again, and again virtually bereft of magnification differences due to breathing. 

For comparison, here’s the Sony 16-50 first at 16mm f22 and focusing from infinity to the closest distance and back again where you’ll notice a more obvious magnification change due to greater breathing. And the same with this lens zoomed to 50mm, where the magnification changes as you focus from infinity to the closest and back again. So in this regard the Sigma wins, exhibiting virtually no breathing at either end of its range.

But the Sigma doesn’t hold all the cards. The Sony 16-50 has a motorised zoom which I may not like for stills, but which allows for smoother and more consistent zooms during video which you may find useful. The Sony lens also includes optical stabilisation for stills and video which you can see in action on this handheld clip, allowing me to hold it steady. Compare this to the Sigma which sadly doesn’t have optical stabilisation, mounted on my A6400 which doesn’t have sensor shift IBIS, so a wobbly combination for handheld video.