both lenses are equally good, as well as its sibling Industar-61 L/Z MC (M42 multicoated version). They definitely are from the very best lenses ever made by USSR - a highly-improved Tessars with close focusing abilities. From my own experience with these I can say that the lanthanum version yields a better color saturation and contrast, also it's claimed to have a better overall resolution. I-61 makes also a good enlarger lens, and gives no flare in all lighting conditions due to its design (built-in hood and small frontal element). I can recommend the lanthanum MC edition - it's improved, really. But a plain I-61 is a great performer, too.
Originally Posted by Dave Wooten