Viltrox 24mm f/1.8 Focus Speed and Performance
As a third-party budget lens, the Viltrox AF 24mm f/1.8’s autofocus performance was always going to be scrutinized under a magnifying glass. And while it didn’t perform perfectly in that regard, it still exceeded my expectations.
In short, the lens autofocuses quickly and quietly, similar to name-brand lenses. I didn’t encounter any issues focusing in low light, and the AF didn’t have difficulty locking onto low-contrast subjects. During my entire time in the field with the Viltrox AF 24mm f/1.8, I relied upon autofocus and never felt the need to switch to manual focus.
That said, in a lab environment, I did notice that autofocus accuracy and consistency were not quite as high compared to name-brand lenses. When autofocusing on a test target, the Viltrox never went wildly off the mark. But it would occasionally front-focus or back-focus to a small degree – detectable in a lab but not obvious in real-world conditions.
As for the lens’s close-focusing capabilities, it’s pretty weak. You get a maximum magnification of just 0.1x (1:10) with the Viltrox AF 24mm f/1.8, which is worst-in-class. It’s fine for larger subjects, but not workable for serious close-up photography.
Distortion
The Viltrox AF 24mm f/1.8 exhibits just 0.83% pincushion distortion as measured in the lab. However, in practice, the distortion is a complex “mustache” shape, and I find that Adobe’s default correction in Lightroom does not do a perfect job eliminating this distortion. Specifically, it corrects the barrel distortion in the center without properly dealing with the pincushion distortion in the corners. Turning the distortion correction up to 200% with Adobe’s sliders helps, but it also leads to more cropping of the image.
In any case, the distortion is not high enough that it’s a big cause for concern. But for critical architectural photography work, you should compose a bit wider with the expectation that the distortion correction will require a slight crop.
Vignetting
In uncorrected images, the Viltrox 24mm f/1.8 has high levels of vignetting, even at narrower apertures. I found myself manually correcting vignetting on more f/11 and f/16 landscape photos with this lens than on any other lens I can recall. Here’s a full chart of vignetting levels:
The maximum of about 2.5 stops of vignetting at f/1.8 is high enough that you’ll need to correct it most of the time. For handheld photography in low light, that negates some of the advantage of this lens’s bright f/1.8 maximum aperture.
Even when stopping down to f/8 and narrower, you’ll still see over a stop of vignetting in the corners. That’s fixable in post-processing, and thankfully, Lightroom and other post-processing software has a built-in profile for the Viltrox 24mm f/1.8 that works well.
Lateral Chromatic Aberration
There is a negligible amount of chromatic aberration on the Viltrox AF 24mm f/1.8 at every aperture. Here’s the chart:
Anything under about one pixel is almost impossible to notice in real-world images, even with chromatic aberration corrections turned off. At these levels, you are unlikely to ever see lateral chromatic aberration on the Viltrox AF 24mm f/1.8.
Sharpness
The moment you’ve all been waiting for! I was curious how the Viltrox 24mm f/1.8 would hold up in sharpness considering that it’s a pretty cheap lens. Here’s what my testing showed:
This is a decent performance – nothing special, nothing terrible. Central sharpness is solid at every aperture, while the corners are weak at f/1.8 and f/2, but sharpen up pretty nicely starting at f/4. For landscape photography at f/8 and narrower, or for handheld photography where central sharpness is most important, I wouldn’t hesitate to use the AF Viltrox 24mm f/1.8.
That said, there is a ton of wavy field curvature on the Viltrox 24mm f/1.8, which is responsible for the low midframe sharpness numbers that you see in the chart above at f/2.8 through f/5.6. Whether field curvature matters in practice depends upon the flatness of the subject. There is also focus shift on this lens – so, for maximum sharpness, make sure to set your aperture first, then focus second.
As for performance at infinity focus, here’s a sample photo at f/5.6 followed by a 100% crop from the bottom right corner:
This is a best-case scenario, with f/5.6 measuring as the sharpest aperture on this lens for corner sharpness. To me, the crop above looks pretty crisp except for the most extreme edge, where it definitely softens some. When corner sharpness is critical, it’s probably best to crop your photos from this lens ever so slightly, or to enable distortion corrections that automatically crop it a bit. When you do that, you’ll have a sharp 25mm-ish lens from corner to corner, at least at landscape apertures.
All in all, the Viltrox AF 24mm f/1.8 is below average in sharpness for a prime lens, but at a given aperture, it’s still better than plenty of zooms.
Off-Center Issue
I’d like to mention one oddity with this lens’s test results, which you may have noticed when looking at the chart in the previous section. Namely, at f/11 and f/16, the midframes consistently measured as sharper than the center on our test chart. Normally, this would indicate a focusing error on my part, so I took a series of 10 photos with slightly different focus distances and graphed the results. You can see that here:
The point marked “Optimal Focus?” gave the highest total sharpness numbers, so I included it in the final MTF results shown a moment ago. However, the center of a lens is nearly always going to be the sharpest point, so why was this lens different?
After looking at a few more tests of vignetting and sharpness at various points in the frame, I believe the answer is that my copy of the Viltrox 24mm f/1.8 was not sitting totally square to the camera sensor. Instead, the lens was sitting up a bit higher than central. (Note that this is different from the commonly used definition of decentering, which involves individual lens elements and harms corner sharpness the most.)
I should point out, it isn’t uncommon for lenses today to sit slightly off-center from the camera sensor. It doesn’t harm a photo’s overall sharpness very much, and it is rarely a cause for concern. However, the Viltrox AF 24mm f/1.8 also has dramatic, wavy field curvature as I discussed a moment ago. Combined, these effects lead to unexpected sharpness results at various points in the frame – especially at narrow aperture values where center/midframe/corner sharpness numbers are already so similar. Hence the results you see above.
This sort of thing is not going to be very relevant to real-world photography. However, I bring it up because it raises some questions to me about Viltrox’s manufacturing tolerances. If I get the opportunity to test more copies of the Viltrox AF 24mm f/1.8 in the lab, I’ll see if it’s a common theme or if I was just unlucky with this copy of the lens.
Bokeh
Bokeh is another word for the qualities of the background blur in a photo. “Good” bokeh is completely subjective, since different photographers have their own preferences for how the background blur looks. That said, photographers commonly want their background blur to be soft, not distracting. Out-of-focus highlights that are round, uniform, and soft-edged are usually considered favorable.
To me, the Viltrox AF 24mm f/1.8 has good bokeh that meets expectations for a 24mm lens. Out-of-focus specular highlights do take on a bit of an edge, and there’s also some longitudinal chromatic aberration (AKA color fringing). But the bokeh is still smooth and not distracting, at least to my eye. Here’s a very typical example:
And here’s a crop of the above photo:
Granted, you won’t tend to get a lot of background blur with a 24mm lens. But if you use f/1.8 and focus up close on a small subject, it’s still a factor. The Viltrox AF 24mm f/1.8 performs just fine in those situations.
Flare and Sunstars
I’m always curious about flare and sunstar performance on wide-angle lenses, since it’s pretty common for the sun to be in your frame at 24mm and wider. Here’s a representative sample photo showing both of these characteristics at once:
In short, the Viltrox AF 24mm f/1.8 has pretty weak sunstars, while the flare performance is good but not great. The lens retains high contrast in backlit situations thanks to the multi-layer nano coating, but there are several colorful dots of flare (both near the sun and away from it) that detract from the performance.
Lens Comparisons
If you’re interested in head-to-head performance comparisons between the Viltrox AF 24mm f/1.8 and some popular alternatives, I’ve written the following extensive comparisons:
- Viltrox AF 24mm f/1.8 vs Nikon Z 24mm f/1.8 S
- Viltrox AF 24mm f/1.8 vs Nikon Z 28mm f/2.8
- Viltrox AF 24mm f/1.8 vs Viltrox AF 35mm f/1.8
I’ve also written a full review of the Viltrox AF 35mm f/1.8 if you want to see how this lens’s sibling performs.
In short, the Viltrox AF 24mm f/1.8 holds its own, but it definitely falls short of the Nikon Z 24mm f/1.8 S in critical performance. Probably not a surprise when comparing a $380 third-party lens to a $1000 Nikon!
The next page of this review sums up everything and explains the pros and cons of the Viltrox AF 24mm f/1.8. So, click the menu below to go to “Verdict”:
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