I just bought a new canon dslr camera and I want to protect the lens. What kind of filter do I need to protect my lens? Is it ok to just leave the "protector" lens? Can I add another filter on top of this lens "protector"? Please help. TY.
Opinions are very divided about using filters to protect lenses. A lens hood and the lens cap should be enough, but if you want a filter, the best option is probably a skylight (clear glass) or UV filter. The skylight can be kept on the lens while others are added in front. The problem with a lens filter is that there could be dust between it and the lens, which obviously shows up as specks on your image. If you do use a filter, it is good practise to remove it occasionally and clean both it and the lens with an appropriate lens cloth.
I dropped a zoom once, which had a skylight filter on it; the filter was buckled and the glass in it broken, but the optics of the lens were okay, so in that instance it probably saved any damage to the lens itself.
The only time I use filters are when I am shooting in either a very harsh environment, i.e. sand blowing around, very dusty, or torrential rain. Then I use a UV. The only other time I use filters is when I need ND's or circular polarisers. Other than that my lenses remain naked. To pick up on what Stormsong states regarding dust becoming trapped between the filter and the front element of the lens. Dust can become trapped in there, but it will actually not show on the image as it is not on the focal plane. You could actually put something as large as a grain of rice on the front element of your lens, and still be hard pushed to detect it on the image. It's all to do with the laws of diffraction and physics and such technicalities.
There are now 'Protector' filters available on the market. Hoya do a pro quality digital protector filter made from toughened optical clear glass that should not effect either the sharpness or colours captured through your lens. It's also multi-coated to prevent lens flair and vignetting. I use one on my everyday carry round lens that stops on the camera at most times and it does a very good job.
Never use filters on my lenses and never had a problem. The lens hood should give you all the protection you need. In the case of my Nikon 14-24mm F2.8 lens there isn't a filter that could be used and the lens hood is fixed and quite small, but never had a problem.