The problem with owning a $900 camera is the fact you always want to buy just one more thing for it. Just one more thing. Just one last thing. The newest one last thing at the moment is a Sigma EX Multi-coated UV Filter, 58mm.
Ultimately, unless you actually need a UV filter (ie, for outdoor shots with a lot of haze, wide open blue sky, or reflective water), you usually just buy one as a way to protect your lens by not having it open to the elements; it’s easier (and cheaper) to buy a new $20 UV filter after you ruin it, than a new $150+ lens.
That said, this filter is optically clear, and doesn’t affect the brightness, color hue, or color saturation of shots, and is made of a single piece of glass with a solid metal frame that screws right into the front of my lens, and my existing lens cap fits over that. So, now I don’t have to worry about cleaning dust and other destructive substances off my lens, since the lens filter seals the front of the lens off from the outside; so I just have to clean the outside of the filter.
It weighs an ounce or two, so it does make the camera feel heavier; not that its a bad thing, I always thought my Rebel XT was a tad on the light side. Even though it weighs more, it doesn’t effect the autofocus function in any way (including the rate at which it focuses), and isn’t heavy enough to cause lens creep1.
I paid around $30 for mine from Adorama, and I’m quite happy with the performance. Since I’ve never owned a lens filter before, I was worried that it would alter the quality of the shots, but it hasn’t in any way. If you own a professional-level camera, I highly recommending buying a Sigma EX Multi-coated UV Filter for your lens(es), too.
: A problem with some lenses where the moving part of the zoom lens slowly moves outwards/inwards when tilting the camera forwards/backwards.