Purists say that filters should not be used, however the reference says that the protective lens has little effect on the image quality:
http://www.dpmag.com/how-to/tip-of-the-week/tech-test-using-filters-for-lens-protection-01-16-12.html#.VAmdERY0_hIAlso: Good discussion saying that little effect:
http://www.dpreview.com/articles/7333331953/should-you-use-a-uv-filter-on-your-lensFilter prices are based on hype and some on quality. For a simple protective filter, you really do not care if the UV filtration is low transmission. Mount material can be a factor, I prefer low cost plastic since it will not damage the lens threads...a sacrificial lamb.
So... Glass... optical or float glass. Historically, no question optical, float was not flat and "perhaps" could affect the image like a fun-house mirror. Historic is not now. Float glass quality is "near that of optical" and of course much lower cost.
http://www.pilkington.com/pilkington-information/about+pilkington/education/float+process/step+by+step.htm
So, I would not be concerned about that and would not pay the high price for "name branded" filters and order direct from china without the name brand put on the same filter.
Oh, Oh, left out an important factor... The caveat is the anti-glare coating. If not coated the light bounced back and forth between the back of the filter and the lens and can cause some loss in quality. To be safe we would buy "Good Known Name Brand" filters, right???
If you buy a low cost filter make sure it says multi- coated. Coatings actually roughen the surface of the glass by depositing partials so that the surface is not mirror like.
So obliviously, the name brands are going to be better...NO, BUNK. Actual testing in a scientific side by side shows some name branded to be the worse... ever heard of Canon, Tiffin (expensive!)both historically good brands ?? yuck!! Mucho$ for junk.
"Camera Lens UV Filter Test: Does multi-coating matter? "
https://www.youtube.com/watch?v=V-ituue1zeoHoya and Promaster came out the best. Hoya now has a "promaster"
There are other youtube videos listed at the right side of the reference video ... too often UHH people give you hype and wet finger in the air (weather prediction) opinions and they are not backed by references. Do not rely on what someones Aunt Sally said... educate your self.
The above is my best estimate without spending a lot of time researching and making it my life's work!! Correct me if I am wrong... But please use scientifically valid reference to back up your comments.