There are a ton of old M42 screw-mount lenses out there for cheap. The catch is that you need an adapter to mount them on modern cameras. One option for Nikon shooters is the Viltrox adapter for Nikon F mount.
The Viltrox adapter does what it claims to do: allow for the mounting of M42 screw-mount lenses onto any camera with a Nikon F mount. The overall build quality is quite nice and there are some well-thought-out features, such as plenty of indents and grooves so you can get enough leverage to remove it from a lens easily.
The advertised standout feature, however, is the glass optical element that, according to the manufacturer, allows the lens to focus to infinity. Due to the thickness of the Nikon F mount, the added thickness of the adapter moves the lens far enough from the film plane to be able to focus to infinity. For a wide-angle lens, this is a major problem. For telephoto lenses, this may not be a big deal (e.g. – for portraiture).
And the Vitrox delivers on that promise. You can indeed focus to infinity with M42 mount lenses on a Nikon body. I tested with a Helios M44 55mm f/2 (my review) and a Rikenon 135mm f/2.8. Both lenses mounted, focused, and otherwise operated as they should on a Nikon D3300 (my review). On the Rikenon, I could actually focus beyond infinity.
I find that the Vitrox adapter adds a sort of soft-focus haze to images, and it definitely contributes extra purple fringing and chromatic aberration. I compared both tested lenses also on a Canon 6D with M42 adapter that did NOT have a glass element. The non-glass adapter images had sharper focus and less fringing.
Vitrox M42 Adapter: The Verdict
For Nikon shooters, I would suggest hunting for old Nikkor manual focus lenses instead of going with M42 lenses and an glass-optic adapter. The overall quality is better and you don’t need an adapter. And, there are some great deals out there on older Nikkors, as well Tokina, Tamron, and other F Mount lenses.