Hi Manfred, thanks again for sticking to my thread
1. I was stupid not to know that I do not have to stick to the diameter 67 mm when choosing a lens. I thought my camera (NIKON D90) can only be fit with this diameter. It is sometimes difficult to find out what lens would fit with my camera (without using adapter. just simply what fits with the camera)
In any case I should choose a lens first and then go for the filter.
2. I find my lens not fast enough. One day I was photo-shooting my friend, dancing in the low light and it was very difficult shooting her movements. I thought it would make it even more difficult for the active photo-shooting if I get the lens like 70-200 mm. Another concern I had was a weight. I already find the current total weight pretty heavy :'(
3. Clear explanation. Thanks
4. I already have a protection filter (it says "MC filter") so I guess I wouldn't go for UV filters then. Not sure if this one removes the ultraviolet (probably not), but I think it's ok for now...
About the confusion I had, I thought you meant there is no big difference between expensive polarizing filters and inexpensive ones very much, and Richard meant opposite. Sorry you both meant the same.
May I ask what the "Multi-coated" polarizing filter?