Just to answer some of your questions:
1. Yes there is no thread to put on your cap, but I think the slimmer the filter the less it interfers with IQ imo. And also to ensure the IQ, there are multiple coatings on the CPL filter to avoid flaring hence the term "MRC".
2. CPL does improve your IQ, less reflections on the object you're shooting. And it's good for shooting indoors too. Details.. that's the word. The only downside is reduced incoming light by 2 stops. But you can always bump up your ISO or use a tripod when shooting fixed objects.
More contrast and details recorded in your shots.
Last edited by kerisabe; 06-20-2008 at 07:58 AM.