One of the greatest Variable ND filters for its price range.Of course, If you are looking for Zeiss grade accessories, pricewise it will cost you something 10x times more and when talking on such precise and high grade attachments for your lenses, Variable ND filters are not the options - you should have bunch of fixed ND filters, with finest and highest grade glass and coating.This one does same if not more as similar Variable ND filters for $50-70, Slim design, so if you stack it on top of standard protective UV filter, it doesn't generate vignet.Glass is fine and high grade - no significant distortion for most $700-$1200 lenses, which I think is not bad, comparable to lens distortion values itself. Again, if you are such picky for distortions and using Zeiss Otus or even Milvus Primes for over $3000, then you should afford getting fixed ND filters from same Zeiss :)If you have DSLR, your backpack is almost heavy enough, so instead of carrying bunch of fixed ND filters for regular outdoor shootings (and weather is coming up and more bright sunny days we'll have :) ), Variable ND filters are desirable lens attachments and for most of APS-C and Full Frame cameras with sensors common 24 MP sensors, this one is one of the optimal solution.BTW, after great medium range tripod from K&F Concept, this is another camera accessory I've got and I like both - great manufacturing quality, nite and clean, functions as it should be and excellent Price/Quality ratio....