I've used both the Helios and various Takumar's, the Helios isn't a bad lens at all but an f1.8 Takumar is definitely better at wider apertures.

My first publish image, a magazine cover was shot with a Helios anda Zenit E, but there's something about the Takumar image quality that gives them an edge. But similar 50mm lenses from the rest of big manufacturers, Canon, Nikon, Olympus etc are just as good they just won't fit the Nova as well.

Ian