UV filters are usually used primarily for protecting the front elements of the lens. There's not much difference in IQ when used in most conditions but cheapo UV filters will tend to give you more problems such as flaring and ghosting when the situation arises.

My Hoya UV filter will sometimes give bad ghosting, reflecting sources of light that is outside of the frame.

Good UV filters will give you lesser problems with flaring and ghosting but the best IQ you can get is without using any filters. How to tell? Just take off your lens filter and look at the front elements of your lens. Can you see much reflections on it? Now mount your filter and look at it again. See the amount of reflections that is visible now. The more reflective the filter is, the more problems it will give you with flaring and ghosting.

Your lens elements is specially coated to minimise problems like flaring or ghosting. That's why they are expensive. Mounting a filter kind of negates the coating's effect on your lens because the glass on the filter will probably not have as good a coating as your lens has.

It's a trade off. Most will bear with a little loss of IQ to protect the lens. Most would rather throw away a filter than a lens. Imagine if a drop of soft drink landed on your lens. Wouldn't you prefer the acid in the soft drink to destroy your filter's coating than your lens' coating?

This post has been edited by shootkk: Jun 29 2009, 09:35 AM

Actually, using a fluorescent light is not the best choice of light source to show flaring or ghosting.

Reason being fluorescent lights flickers! We can't see it with our eyes as it flickers much too fast for us but the camera is able to capture as it goes through its cycles.

Those yellow or sometimes brown colour patches are caused by the flickering of the tube. You can try it. Set your cam to continuous shots, aim it at the tube and fire away. You can get similar kind of yellow or brown patches in some of your shots.

It's not recommended to use CPL for indoors unless you want it specifically to cut some reflection on some surfaces. If you want protection then use UV. CPL more for outdoors. CPL as protection is overkill plus it cuts down on light.

If you want best IQ and you're shooting indoors with no obvious hazards then just remove all filters lor.