When to worry about vignetting?

[tikkeltokkel]

i am going to get the 17-40L and read the day about slim filters. I havent owned a wide angle lens before and already own a 77mm circular polariser (not slim) when i get my multi coated UV for the new lens must it be slim to avoid vignetting at 17mm and will my current polariser be okay ... theyre so darn expensive!?

[PaulB]

I don't think you need to worry about vignetting - especially if you are using a 10D - with the 1.6 crop factor.
However some people have reported that some filters sit too close to the front element on the 16-35/2.8L and touch the front element as it moves forward. Mine doesn't but it might with a very slim UV on the front - it is very close. Check your 17-40/4L to see if this could be a problem, a very slim filter could be worse than a normal thickness one.
I think that Canon say that the 16-35 and 17-40 should be fitted with filters as a matter of course to effectively seal the front of the lens anyway.

[jmublueduck]

you'll be fine. I use a standard B&W UV filter on my 16-35 & don't get any vingetting, nor does the front element hit it.

so don't sweat it ;)