Importance of good quality filters
With the mass proliferation in the supply of filters due to the increased demand of lenses, did anyone ever wonder what are exactly the differences between a good filter and those inferior types, and how would it affect your images?
Good quality filters (usually the more expensive ones) are those that undergo precision double sided polishing process to ensure a certain standard to be achieved for parallelism. The difference would be apparent when taking pictures at telephoto position. At 100% view, those taken with 'unpolished' filter would show a high level of image degradation in terms of picture clarity. Those that are polished would not compromise on image clarity and would produce a crystal clear image as though no filter is attached to the lens.
Another importance feature to look out for is the coating. It is of paramount importance that filters must be 'multi' coated so that your images would receive maximum light transmission (usually >98%) and minimal reflection (<1%) to produce a well exposed beautiful picture. The uncoated version, on the other hand, would only allow approximate 85% of the ambience light to enter the lens and also causes light reflection of up to 5%. The result: The captured image would have low lighting and higher reflection which then lead to the degradation in image clarity.
So when looking for filters to protect your valuable lens, always ensure that you are getting the best possible filter (that would fit into your budget) without compromising on the above mentioned points (or at least to a certain acceptable level).