UV FILTER 有何分別？

CPL = circular polarizer - used to take photo of water to minimize reflection
- used to take photo of sky and landscape - blue sky & sharp pic
- used to take image through glass to cut down reflection as well
- used to take image of model to reduce oily face
need to rotate the ring to adjust the effect of reducing the reflection, etc. if use potable light meter, need to increase aperature size to allow sufficient light, not affected if use TTL metering

UV HMC - UV filter with coating
both UV and UV HMC are usually used as protection to lens. Some expert would rather not use filter because they think it will affect quality of image
other saying is to buy the most high end filter at 77mm (cost almost $800-1000) and use step ring to fit all lens with different diameter.