This is not the first M42 300mm lens I have. I had a Vivitar 300mm f5.6 but the optical quality was somewhat lacking. I was fortunate to acquire the Takumar 300mm f4 recently (Thanks Stuart!).

Very light for its focal length, especially when the tripod ring is removed.

Took some quick shots with the slow, dinosaur like Kodak SLR/c, and I am extremely happy with the results. Sure, most of the shots are blurry, but not due to the quality of the lens, but focusing hand-holding issues. This lens is absolutely usable wide open too, which is unbelievable for a lens of this vintage.