Since you own a couple of filters and need some info i refer you to these two sites www.camera-filters.com and www.kaya-optics.com..... Just before i saw this post i was viewing those two sites. The first referenced sight i believe it was gave a good description of when and where to use some filters ..EX was the circular polarizer lens you talked about... I hope this helped some... I was looking to find a infra red filter for my xl1 camera Its of course the 72mm size and i am finding difficulties finding it.Do you know any sites i can find a infa-red filter for the Canon xl1???????(posted 8369 days ago)