I must admit I normally avoid using them on ultrawides, because I much dislike the uneven effect. On your 17-40 you'll have less of a problem at the longer end, so it is probably still worth it.
I'm going to be buying the 24-105L which is also 77mm filter size so think I'll give it a go then, thanks
Next question, are "slim" filters necessary or is that only if i want to stack at 17mm with say a nd and c.pol?


















