Originally posted by mrdogbear
For Q1, what is the diff between high end UV filter and low end UV filter? only the ability of reducing UV makes diff? If I buy a low end one, will it affect photo quality or become darker?
Since you're using a digicam, the actual UV absorption function of the filter doesn't really matter all that much, because digicam sensors are basically insensitive to UV radiation (or at least certainly much more so than film).
As such, the only real reason one might want to get a UV filter is for protective purposes, because if anything happens to scratch or otherwise damage the front element of your lens+filter tube, it's much cheaper and easier to replace a $10 filter than to repair a lens that costs hundreds or thousands of dollars.
That being the case, you will want a filter that basically leaves the incoming visible light radiation completely unchanged, so that you don't end up sacrificing image quality just for protection (what's the point of getting an expensive super-sharp lens if the filter you stick on top of it ruins the image?). This is where filter coating quality comes into the equation. Basically, the idea is that every additional glass-air interface you add will result in some light being reflected, and you may end up with unwanted internal reflections within the lens tube--and these will show up as rather distracting out-of-focus spots on your image. This is typically called "lens flare".
While reflections are inevitable, filter coatings reduce the amount of reflections tremendously; as mervlam posted, an uncoated UV filter typically reflects about 4% of incident light (note that this occurs on
both surfaces of the filter), whereas a good multi-coated filter will reflect only about a small fraction of a percent (i.e. much less than 1%) of incident light. This difference may not be obvious when you observe each filter on its own, but put two such filters side by side and the distinction should be (literally) very clear. For instance, I sometimes mistake my Hoya SMC UV filter for a step-up ring, because I don't notice that there is glass inside it.... (ok, this is really embarrassing... :embrass: )
The downside of multi-coated filters is that they are (a) more expensive; and (b) more difficult to clean. Let me also qualify what I wrote above by saying that multi-coated filters are
not absolutely essential--no one piece of equipment in photography ever is--but they are certainly good to have. I would at least seriously consider investing in one if I were intending to leave the filter on my lens all the time.
