The first thing I do when I buy a new lens is put a “UV Haze filter” on the front, mainly to protect the lens. If you ever have something hit the front of your lens and scratch it, it is cheaper to replace the filter than to replace the lens.
Every lens I own has a filter on it to protect it. There are times where you might need to take it off, if the extra layer of glass causes any problems with light flare or reflections. That is most likely to happen if you are pointing the camera toward light sources such as street lights at night or looking toward the sun.
You will find some people who believe putting any additional layer of glass on the front of a lens degrades the image quality, but frankly that impact is so very small, it is really negligible compared to the value of having the protection provided by the filter. The only time it is really a concern is if there is a problem with flare.
Most lenses show their filter size in millimeters (mm) somewhere on the lens, usually on the front. The filter size is not the same as the focal length. So, look for the right filter size before you make a purchase!
Be safe or sorry!
Happy Picture Taking!
Kevin Gourley
I would much rather replace a clear/UV haze filter then a lens any time! However, it is a personal choice.
Here is a link I found useful about use of filters:
http://www.the-digital-picture.com/Reviews/UV-and-Clear-Lens-Protection-Filters.aspx