Viltrox AF 28mm F4.5 FE review: tiny, cheap, and a little bit weird

While full-frame mirrorless cameras now dominate the market, the lenses to fit them have tended to become larger, heavier and more expensive than their DSLR equivalents. But Viltrox has decided to buck this trend, with its tiny Viltrox AF 28mm F4.5 FE. This lens is a mere 15mm long, weighs just 60g, and costs under $100 / £100. That makes it by far the smallest and cheapest autofocus lens you can buy for full-frame mirrorless cameras. Initially at least, it’s available solely in Sony E-mount.

Viltrox AF 28mm F4.5 FE at a glance:

• $99 / £99
• Ultra-compact pancake / body cap lens
• 32cm minimum focus
• 15.3mm long, 60g
• Sony E-mount only (full-frame)

To get some perspective on what Viltrox has achieved here, we just need to look at the alternatives. Previously, the smallest full-frame autofocus lens for Sony cameras was the Samyang AF 35mm F2.8 FE, which weighs just 86g, but is more than double the length (33mm). Even if we consider APS-C format optics, the Viltrox 28mm F4.5 manages to be slimmer and fractionally lighter than the tiny Sony E 20mm F2.8.

Looking at other mounts, the slimmest full-frame AF lens overall was previously the Nikon Z 26mm F2.8. But even that is 24mm thick. Indeed somehow, Viltrox has managed to make this lens smaller, lighter and cheaper than the L-mount Panasonic Lumix S 26mm F8, which is manual-focus only, fixed aperture, and gathers little more than a quarter of the light.

Unsurprisingly, Viltrox has made some significant compromises to achieve this tiny size – and some plain eccentric design decisions too. Most obviously, there’s no manual focus ring, the aperture is fixed at f/4.5, and you don’t even get a filter thread. So is this lens really just an attention-grabbing gimmick, or could it be a genuinely useful addition to photographers’ kit bags?

Features

Given its low price and small front element, you might think this lens has skimped on the optics. But as indicated by the ‘VCM ASPH ED’ on its front, that’s not entirely the case. Its 6-element, 6-group design includes two aspherical elements and two made from extra-low dispersion (ED) glass. As tends to be the case these days, most of the glass is concentrated towards the back of the optical unit, with the rear element being dramatically larger than the front, at 26mm in diameter.

Autofocus is driven by a voice coil motor (VCM), with the 32cm minimum focus distance delivering a rather modest 0.11x magnification. There’s no fancy internal or floating focusing mechanisms here, either, with the entire lens moving back and forth as a unit. There’s no adjustable diaphragm, but there is an unusual octagonal aperture plate over the front element – more on this later.

You get no means of attaching filters or a hood, or even a front lens cap. Instead, there’s a built-in cover for the front glass, which is opened and closed using a small lever on the front. This results in a design that’s strongly reminiscent of Olympus’s ‘body cap lenses’ for Micro Four Thirds.

While the lens is designed for Sony’s full-frame cameras, it also works perfectly happily on APS-C models. Here it provides a ‘perfect normal’ focal length equivalent to 42mm on full-frame. This means that when used on Sony’s A6000-series cameras, it imparts an extremely natural-looking perspective to your images.

Firmware updates

Flip the lens around, and you’ll see that Viltrox has embedded a USB-C port in the mount. This is used for updating the firmware, although in a somewhat unusual fashion, via Viltrox’s smartphone app. Firstly, you have to download the app and create an account. Then, connect the lens to a USB-C power supply. This fires up a Bluetooth chip inside the lens, which the app will find, and prompt you to create a connection.

Once connected, the app reads the current firmware version. If an update is available, it’ll prompt you to install it, which again is done wirelessly. It’s all a bit unusual, and nowhere near as easy as connecting the lens to a computer and copying an update file across, as with the firm’s other optics. But it does work.

Build and handling

Despite its bargain price, the Viltrox AF 28mm F4.5 comes across as perfectly decently built. The mount is metal, and the slender plastic barrel doesn’t flex in any way. There’s a nice, ridged grip around the outside which helps with attaching the lens to your camera and removing it after use. It’s all rather nicer than the Samyang AF 35mm F2.8 FE, which feels decidedly cheaply built, in comparison.

Of course, given its tiny dimensions, the lens adds practically nothing to the size or heft of your camera. Even on Sony’s smallest APS-C bodies, it barely extends beyond the handgrip. Use it on full-frame A7-series models, and you’ll hardly even notice it’s there. You could, entirely plausibly, use it instead of a body cap when travelling, which I guess is the whole idea.    

Unusually, when the front cover is open and the lens isn’t powered on, the optical unit slides freely back and forth within the barrel. In fact, it appears that one of the functions of that cover is to lock the lens in the infinity position, so the glass doesn’t rattle around inside. At its minimum focus position, the front element pokes out a couple of millimetres past the cover, and almost flush with the front of the housing.

As a result, Viltrox advises that you should always open the front cover before turning on your camera. This is because the lens goes through a calibration cycle when the camera is switched on, which involves rapidly racking it through its full focus range. So if the cover is closed, the front of the lens will end up pressing against it.

You will, of course, inevitably forget to do this on a regular basis. Thankfully it doesn’t appear to damage the lens, but it can cause operational problems with older cameras. You may have to switch them off and on again, or even remove and reattach the lens, for autofocus to work.

Autofocus

In general, most unit-focus lenses autofocus rather slowly and hesitantly, simply because the focus motor has to move around a relatively large amount of mass. But thanks to its voice coil motor, the Viltrox AF 28mm F4.5 FE generally autofocuses pretty well. However, that relatively slow aperture does mean it can struggle a bit in low light.

I used it on a number of cameras, ranging from the APS-C Sony A6000 from 2014, through to the 60MP full-frame Sony A7R V from 2022. In general, it autofocuses quickly and essentially silently, and I saw no problems with accuracy, either. However, with my old Sony A7 II it appears to use contrast detection only, which makes it decidedly sluggish.

As this is a unit-focusing lens, the angle of view does narrow visibly on focusing closer. Such focus breathing is of little consequence to photographers, but videographers will want to avoid pulling focus between subjects during recording.

While there’s no focus ring on the lens, this doesn’t mean that manual focus is entirely unavailable. You can, if necessary, adjust the focus using either a Bluetooth remote control, or with more recent cameras, Sony’s Creators app on your phone. But it’s a clunky process.

Performance

Obviously, it would be crazy to expect a sub-£100 lens to perform as well in terms of image quality as a premium optic costing ten times as much. But I was pleasantly surprised by the images I shot with the Viltrox AF 28mm F4.5 FE. As long as you don’t get too hung up on pixel-peeping, especially towards the corners of the frame, it’s capable of delivering rather nice results.

As there’s only one aperture on offer, analysis of the optical performance is pretty straightforward. The lens is impressively sharp in the middle of the frame, even on the 60MP A7R V. This pixel-level crispness fades gradually towards the edges, with things getting noticeably smudgy in the corners. Sharpness is maintained well throughout the focus distance range.

That fixed f/4.5 aperture does, however, mean that with real-world subjects, plenty of the scene will be slightly out-of-focus. You won’t really get much in the way of ‘bokeh’ as such – just areas that aren’t perfectly crisp.

This is where the concept of depth-of-field comes in, of course, and often these parts will be ‘sharp enough’ if you look at the full image instead of the pixels. Indeed most of my images looked absolutely fine full-screen on my 24-in monitor, which means they should be good enough for A3 prints.

Viltrox doesn’t appear to make any use of in-camera lens corrections for either distortion or chromatic aberration. However, distortion is very well-corrected optically. There’s perhaps a little pincushion-type bending of straight lines along the edges of the frame, but it’s unlikely to be a problem in real-world use. Adobe software now has the requisite lens profile to correct it fully.   

If you disable shading compensation, you will encounter significant vignetting, and of course you can’t stop down to reduce it. However, it does get suppressed pretty effectively by the in-camera compensation function.

Of course, if you use the lens on an APS-C camera, you won’t see much vignetting at all, as those dark corners mostly get cropped out.

Lateral chromatic aberration can be visible in the form of red/blue fringing along high-contrast edges towards the corners of the frame, even in JPEG files. This is something we don’t see much these days, as usually it’s corrected in-camera. But the effect isn’t huge, and it’s generally a one-click fix in raw processing.

Where things get somewhat funky with this lens is when shooting into the light. With essentially no shading of the front element, can be prone to spectacular flare spots when the sun is just outside the frame. However, you can see this in the viewfinder, and often slightly adjust the composition or shade the front of the lens with your left hand to make it go away.

With bright point light sources within the frame, that octagonal aperture plate on the front kicks in, generating 8-point starburst patterns. It’s an interesting design decision, but I’m not entirely convinced by the effect. If the sun is within your image, the resultant rays can stretch all the way to the edge of the frame, even on a full-frame camera. This makes the effect so strong as to be overbearing.

Viltrox AF 28mm F4.5 FE: Our Verdict

With its AF 28mm F4.5 FE, Viltrox has done a clever job of cutting the design right back to make a true “body cap lens”. It’s pretty amazing that something this small, light and cheap covers full-frame and can still autofocus. It feels churlish to criticise it in any way.

That 28mm focal length can be quite a nice option on both full-frame and APS-C cameras, although in distinctly different ways. I initially thought that the fixed f/4.5 aperture would be neither fish nor fowl: too small to be much use in low light, but too large to deliver sufficient depth-of-field for general photography. And while it’s true that this isn’t a great lens for night-time or indoor shooting, it worked much better than I expected for such things as cityscapes and landscapes.

But does it really make sense? Obviously, nothing can beat it when you really want to minimise bulk. It’s perhaps easiest to recommend to APS-C users, as its tiny size is a great match to A6000-series bodies, and you only see the best part of the optics. But I’m not quite so sure about full-frame. If you’re carrying around a larger A7-series camera anyway, I’d be inclined to go for a more conventional compact prime.

Ultimately, the Viltrox AF 28mm F4.5 FE provides a unique option that no other lens can match. But it’s precisely all the things that make it so small and cheap – the lack of a focus ring, aperture mechanism, or focus thread – that could leave users frustrated. And its starburst effect is, frankly, a bit odd. It isn’t just a gimmick, but I wouldn’t want it to be the only lens I was carrying.

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Viltrox AF 28mm F4.5 FE: Full Specifications

Price	$99 / £99
Filter Diameter	n/a
Lens Elements	6
Groups	6
Diaphragm blades	n/a (octagonal front aperture)
Aperture	f/4.5
Minimum focus	32cm
Length	15.3mm
Diameter	60.3mm
Weight	60g
Lens Mount	Sony E
Included accessories	Rear cap