The Viltrox PFU RBMH 20mm f/1.8 ASPH enters a rather crowded space but it has a couple of differentiators that set it apart from the rest of the gang. There is, of course, the fast maximum aperture of f/1.8. The image quality is perfectly fine in the image center whereas the borders are quite soft. This may or may not be important depending on the target application. If you are into shallow depth-of-field photography, this isn't really an issue for instance whereas for astro photography this isn't ideal. If you stop down, the quality improves quite a bit and it's really good at medium aperture settings. Lateral CAs are low and you don't have to worry about image distortions either. The vignetting is on the high side though. The quality of the bokeh (out-of-focus blur) is pretty good for a lens in this class.

The build quality is excellent thanks to a tightly assembled, all-metal-construction. The price you have to pay for the solid body is the high weight and it isn't a small lens either. Weather-sealing is not provided but that's no surprise at this price point. If you are into videos, you will love the dampened control rings and yes, it has a step-less aperture ring - but no stepped mode. On the downside, it's a fully manual lens with no coupling so if you can't live without AF, a camera-controlled aperture and EXIF data, this lens is not for you. The Viltrox lens comes with two different lens hoods - one that is optimized for the job and a 2nd one that accepts conventional, albeit large filters (82mm). It's a smart approach to have the choice without having to rely on aftermarket solutions. The quality of the lens cap could be better though.

Another differentiator is, of course, the price. At just under 400USD/EUR, it is not only very affordable, but it is also almost a steal considering the large aperture.