Firstly, I have to say that this is, all in all a good, useful filter and totally worth the price. I'm only taking one star off for some aspects of its performance where I thought it would do better, and another for a problem I fixed myself with a little maintenance, but should really not have been there.As far as stopping light - this filter performs as advertised! It does cause a brownish cast over images at nearly all settings, which can really reduce the vibrance of colours - something you can pretty easily restore in post-processing, but it does mean making that extra step.This filter performs very well for me on lenses between 28mm and around 60mm focal length. Where I was a bit disappointed with it was at longer focal lengths - because with those, it not only mutes the colours, but begins to effect image sharpness, and that is a no-no. Worse, I noticed it doing that a bit unevenly across the image.Closer examination showed that the filter has signs of what seemed like water or oil stains on the inside, between the two glass layers. I ended up taking the filter apart and cleaning the inside surfaces myself - the stains, happily, were not permanent and wiped away neatly after a very light cleaning with ROR liquid. Still, this is something that the filter should not have shipped with and could've been easily quality-controlled.I still find that it doesn't quite perform well on longer lenses - but it's handy on my vintage "nifty fifties". It's just that if I knew I wouldn't be too happy with the filter's performance at longer focal lengths - I would've bought it in a smaller thread size than 72mm.So, my recommendation: if you want an affordable variable ND filter for use on lenses between 28 and 60 mm focal length - go for one that fits your filter thread. Your lens(es) in that range are more likely to be somewhere between 49mm and 58mm, maybe 62mm filter thread. No need to buy a larger 72mm filter for those! And for anything larger/longer - I recommend looking into a higher-quality filter. Even K&F concept actually has some much better ones, albeit for about double the price.