Hi all,

I was looking to buy a Lee Big Stopper recently and was talked out of it by a salesman who advised the brand Nisi was the same quality but a bit cheaper. So, I ended up buying the NISI as others seemed to like it. It's meant to be a 10 stop filter but I'm having trouble believing that. Today it was overcast so I used it on mt 24-70 2.8 at F11 on AV and it stretched it out to 30 seconds, which was fine, but anything more than that and it won't handle it. I've read of people in low light being able to use them to exposures of a few minutes but not this time.

Any advice? Are they good or have I been had?