circular polariser?

Ok been thinking of getting a circular polariser for my lens(17-40L, and 70-200L) im looking for a 77 mm to fit, and wondered if i need to get a 'thin' type ? as ive heard stories of vignetting on some wide angle lenses, would this affect my 17-40L on a 20D? (or will a 'normal one be ok?)
I called into my local store and they wanted £125.00 for the hoya pro one , can anyone suggest a cheaper 1 (but still need good quality).
Yes i know i need to look around but would appreciate suggetions for other good/reputable makes before i check the prices out
thanks phil

it will vignette anyway, and with a thin the lens cap won't work. just get a normal and don't use any other filters with it.

thank corey the lens cap isnt to much of a worry as i would only be using the filter as and when reqd so the filter wont be on it when i put the camera away.any suggestions for other makes?

A normal 77 mm filter shouldn't vignette on the 17-40 on a 20D. If you upgrade to FF, you might have a problem, but for an APS-C camera I think you'll be OK.

I use a thin B+W multicoated on my 17-40L. No vignetting and I don't mind the friction-fit cap.

philbyuk wrote in post #2191294
Ok been thinking of getting a circular polariser for my lens(17-40L, and 70-200L) im looking for a 77 mm to fit, and wondered if i need to get a 'thin' type ? as ive heard stories of vignetting on some wide angle lenses, would this affect my 17-40L on a 20D? (or will a 'normal one be ok?)
I called into my local store and they wanted £125.00 for the hoya pro one , can anyone suggest a cheaper 1 (but still need good quality).

I use Sigma's thin CPL for my 10-20 and 17-40L. It is threaded so your lens cap will fit on it. I'm quite happy with it and recommend it. It was US$140, which is a bit less?

thank you all for your replies will look at the alternatives

You've got to consider the other brands Like B + W, Heliopan, and Hoya...

I'm researching to purchase additional 77mm filters, including the Circular Polarized Filter...there really aren't that many choices or brands offering a quality multi coated CP when sorted out...I'm now sorting by price to see what the best one is that I can afford...

Go to the vendor web sites and sort by type, size and price, and compare...You'll be surprised at the few to choose from at your estimated cost of purchase.

Heliopans are all "slim" style now, but maintain front filter threads for use with lens caps. B+W I'm not as familiar with but are also of very high quality otherwise. Next up are typically Hoya Pro1 filters.

Not all "slim" types have front threads. As long as it does then you can still use a cap. I might suggest picking up a "Tamron style" cap, which has extra pinch areas in the middle of the cap, making removal much easier with a hood affixed - and fit better on slim filters since the thread depth is less than the average Canon cap.