Introduction
The newest kid in Viltrox’s ever-growing list of prime lenses is the AF 15mm f/1.8 Air XF – an APS-C format wide-angle lens equivalent to roughly “23mm f/2.6” (full format). It’s a quite attractive focal length with applications such as landscape, architecture, or street photography. It is available in E-, Z-, and X-mount for 239 USD / 269 EUR / 229 GBP / 335 CAD / 39,000 JPY, which is very affordable compared to OEM standards. We’ll discuss the X-mount version in this review.
The 15mm f/1.7 is a member of the “Air” lineup which is about delivering affordable lenses with a small form factor. Despite the lightweight, the build quality is pretty decent, with the lens body made of good-quality engineered plastics based on a metal mount. The broad (plastic) focus ring turns smoothly. A petal-shaped lens hood is supplied. There are no buttons on the lens. Thus, you have to switch the AF on/off via the camera menu. Weather-sealing is not provided which is not overly surprising given the price point.
You won’t really need lightspeed AF on such a wide lens, but the STM (stepping motor) is both pretty snappy as well as silent. Firmware updates are possible via a USB-C port on the mount.
| Specifications | |
|---|---|
| Optical construction | 12 elements in 10 groups, incl. 2x aspherical, 3x ED, 3x HR |
| Number of aperture blades | 9 |
| min. focus distance | 0.23m (max. magnification 0.1x) |
| Dimensions | Ø 65 x 56.7m |
| Weight | 180g |
| Filter size | Ø 58mm |
| Hood | petal-shaped (bayonet mount, supplied) |
| Available Mounts | Sony FE, Fujifilm X, Nikon Z |
| Other features | USB-C port for firmware updates |
Distortions
So far, Viltrox doesn’t provide an auto-correction profile for image distortions in their “Air” lenes, so you will have to live with the original optical correction. Technically, the image distortions are very low at just 0.3%. However, the distortion characteristic is wavy, which may be noticeable in critical scenes at least.
Vignetting
The Viltrox lens is very compact given its maximum aperture settings, and it shows in the vignetting results. At f/1.7, the raw vignetting is very high for an APS-C lens. The light falloff is still higher than our usual APS-C scale at f/2.2 and doesn’t drop below the 1 EV mark even at f/5.6.
Auto-correct does tame the vignetting at large aperture settings, less so at medium apertures.
MTF (resolution) at 26 megapixels
The Viltrox AF 15mm f/1.7 Air XF produced pretty good results for such a wide and fast prime lens. At f/1.7, the center quality is already up there, although there is a fairly steep drop in quality towards the corners. The corners are only slightly soft. Stopping down to f/2.8 boosts the border center as well as the corners. The technically best results are achieved around the f/4 mark where the outer image field reaches very good levels. Diffraction effects set in beyond, and you shouldn’t use f/11 unless you really need the depth-of-field.
The centering quality of the tested sample wasn’t great with a tilted focus plane making it tough to come up with a statement about the field curvature.
Please note that the MTF results are not directly comparable across the different systems!
Below is a simplified summary of the formal findings. The chart shows line widths per picture height (LW/PH) which can be taken as a measure of sharpness. If you would like to know more about the MTF50 figures, you may check out the corresponding Imatest Explanations.
Chromatic Aberrations (CAs)
Lateral CAs are low, with a peak CA pixel width of around ~0.4px at the image borders.
Sun Stars
Below is a sequence of 100% cropped images from f/1.7 all the way up to f/16, illustrating the sun star behavior. Sun stars are an aperture effect that shows up if a bright light source is part of the scene (usually in night shots). Due to the circular aperture shape, the sun stars are non-existent at f/1.7. Beyond, they slowly fade in (with a strange “drop” at f/5.6) and they are getting more obvious at f/8. At f/8 and f/11, the rays are “fan-like” which most won’t consider as overly attractive. The rays are becoming pointy at f/16, though.
Competition
There is currently no other 15mm lens available in X-mount. However, there are a couple with a 16mm focal length. There is, of course, Fujifilm’s own XF 16mm f/2.8 R WR. It’s one of the classic Fujifilm prime lenses and highly attractive due to its small size, weight, and build quality. It is much slower, though. Conversely, the Sigma 16mm f/1.4 DC DN Contemporary is faster – but also much bigger.
Sample Images
The following images were taken with an X-H2 at 40 megapixels. Thus the corners are somewhat softer than the MTFs @ 26 megapixels suggest, of course. The mentioned centering issue (tilted focus plane) is also somewhat visible.
The Viltrox AF 15mm f/1.7 Air XF is another welcome addition to their ever-increasing prime lens lineup. At least on 26-megapixel sensors, the sharpness is perfectly fine from f/2.8. At f/1.7, it's quite usable at least. A 40-megapixel sensor is more challenging, but this applies to most lenses really. Image distortions are on a low level, albeit a bit wavy. The vignetting is a bit on the high side which doesn't come as a surprise given the compact size of the lens. Sun stars aren't a big strength, if that's your thing.
The build quality follows the tradition of the other Viltrox Air lenses. The engineered plastics are of good quality, and everything is tightly assembled. While it doesn't have any kind of weather sealing, the internal focusing mechanism should provide at least a bit of protection against dust. The AF uses an older-style STM motor. However, it's still pretty fast and essentially silent.
It may not be the most fancy lens around, but budget-oriented users may certainly appreciate a lens that is decent, surprisingly fast and which still doesn't cost an arm and a leg
Viltrox lenses are available via the usual suspects such as Amazon or B&H, or directly via the Viltrox Store.
The Good
- Great Value
- Quite sharp at medium aperture settings
The Bad
- High Vignetting for an APS-C lens
- Maximum object magnification is just 0.1x
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Optical Quality
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Build Quality
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Price / Performance