The wide-angle camera on the Samsung S9+, along with its smaller S9 sibling, comes with an adjustable aperture, offering either F1.5 or F2.4.

In a never-ending quest for better image quality, smartphone manufacturers are turning to all sorts of tricks to eke better performance out of very small image sensors. But through all the software, algorithms and dual-and-triple camera setups, the Samsung Galaxy S9 and S9+ flagship phones have joined a very select club of smartphones with real aperture settings. The S9+ will automatically switch from F1.5 to F2.4 depending on your lighting situation, and you can manually select it in 'Pro' mode.

Going from F2.4 to F1.5 on the Galaxy S9+ gives you nearly a stop and a third of extra light

So what are the potential benefits of having aperture control on a smartphone anyway? According to Samsung, "the category–defining Dual Aperture adapts to bright light and super low light automatically, like the human eye. And you can flex your artistic side, toggling the aperture to create a mood."

Just 'flexing my artistic side' by manually choosing F1.5 and shooting into the sun. Out-of-camera JPEG.
ISO 50 | 1/516 sec | F1.5

All that strikes us as a little 'over-the-top,' but there is some potential here. Going from F2.4 to 1.5 gives you nearly a stop and a third of extra light, and will keep your ISO value down (or your shutter speed up) in dim conditions. But we were also curious about the quality in other situations; after all, these apertures are equivalent to F9 and F14 on full-frame. Could shooting the wider aperture in bright light give you sharper images by having less softness from diffraction?

Landscape quality

As you can see in a variety of areas, this isn't the case - the corners in particular are softer at F1.5.

F1.5 F2.4

Here's an easy-to-see example of the difference in detail capture, despite all the Galaxy S9+ is doing behind the scenes to make these look as detailed as possible. It's important to put this in context, though: when flipping between these two images full-screen on the S9+ they look identical. So unless you're planning on making prints from your cell phone landscapes, it probably doesn't matter all that much which aperture you (or the phone) pick.

Let's see what sort of difference the aperture makes with a close subject, and distant background.

Close focus quality

Disappointingly, the S9+ and its included applications don't allow you to use any computational background blur wizardry on images shot using the wide-angle camera that it does allow on its telephoto one (the smaller S9 on the other hand, which only has a wide angle camera, does let you do this). So does having a wider aperture give you some buttery background blur naturally?

While there is a difference in background blur between the two apertures, it's nothing like shooting with a wide-aperture prime lens on an interchangeable lens camera - but nor would we really expect it to be. But we do see how the phone's noise reduction techniques deal with fine gradients in out of focus areas.

F1.5 F2.4

Low light performance and takeaways

In really low light conditions, the faster aperture will definitely get you better shots on the Galaxy S9 and S9+ than if you were forced to use the camera at F2.4. Optical image stabilization means that you can hand-hold images down to a reasonably slow shutter speed, and the phone can keep its ISO more than a stop lower - as long as your subjects aren't moving.

Out-of-camera JPEG.
ISO 50 | 1/13 sec | F1.5

But as I found out while shooting a dimly lit concert with the Galaxy S9+, Samsung's latest flagship camera phone still isn't a match for low light and moving subjects in its fully automatic mode (you can switch into 'Pro' mode and force higher ISO values or shutter speeds if you're an advanced user). We are still working through our testing and plan on doing side-by-side comparisons with phones such as Google's Pixel 2, which intelligently stacks images together even in low light situations.

This photograph taken at 1/30 sec in 'auto' was the only one that wasn't blurred to oblivion. Out-of-camera JPEG.
ISO 800 | 1/30 sec | F1.5

Now it's true that for casual shooters taking their phones out to dinner and photographing their friends and their food, the camera will automatically switch to F1.5 will help them get shots with more detail and less noise reduction, while using an F2.4 aperture will get them slightly better quality in daylight.

But we can't help wondering if this is a little 'gimmicky' - the drop in detail at F1.5 is unlikely to be a deal breaker for these sorts of users, and if Samsung didn't have to squeeze an aperture blade system into the lens design, could they simply have made the lens perform better wide open? The system looks to have real blades that expand and contract, but you're only allowed a toggle between the two values.

We don't know for sure, but we've still got lots of testing on the Galaxy S9+ over the coming weeks. Stay tuned for our full review.