In reply to The Lemming:
I suspect a UV filter is only useful for protection purposes on a digital camera due to the spectral response of the sensor. "Plain" glass actually blocks UV anyway, so a UV filter probably is just "plain" glass (which is why they are so cheap).
This page explains what the spectral response of the camera is and how you can measure it
http://vitabin.blogspot.co.uk/2013/04/spectral-response-of-nikon-dslrs-d90....
This plot shows another response of DSLR. I have no idea if it's representitive of whatever camera you have.
http://www.astrosurf.com/buil/50d/canon_5d_5d2.png
You can see from the plots that for wavelengths shorter than about 410nm, the sensor is pretty much insensitive. Granted the graph stops at 400nm, but other similar graphs show the response staying low.
Here are some plot showing the spectral response of various filters including a UV filter.
http://www.giangrandi.ch/optics/filters/filters.shtml
The plot shows that the 75% cut off of the filter is about 410nm, so above 410nm, pretty much all of the light goes striaght through. Only below 410nm is the filter doing anything.... and the camera is already completely insensitive to this wavelength.
Therefore for these sensors, and this UV filter, the only effect of the filter is to block a small amount of the light at the blue end which might make the image marginally warmer (which you could do trivially in software anyway). Therefore the conclusion is that this UV filter does nothing for the overall spectral response.
Search around on some of the amauter astronomy webpages for more information. A common modification is to remove the built in IR blocking filter to improve the camera sensitivity to 650nm (almost infra red) which is a very particular colour emitted by ionised hydrogen.
