Sunday, 1 March 2015

What is the downside of a cheap UV filter that is used solely for the protection of the lens?



I have a Canon EF 17-40L, and I am seeking to buy a UV filter solely intended for the protection of the front glass of the lens. I know that I have a hood for protection, but it makes the equipment bulky and it doesn’t fit my current bag, so I think that a UV filter is also a good solution.


I have seen lots of cheap and expensive UV filters, but I don’t understand the difference between them. What would be the possible downside of using a cheap UV filter in this case? Does it cause the lens flares, and/or reduces the light? I have read some related posts from SE, but they are more general, rather than explaining the differences between filters.



Answer



Cheap is not necessarily cheap - you can get a cheap filter that is good, but if you get one that is bad, the following are side effects that have been reported/observed by other users:



  • focussing problems with cheap UV filters

  • loss of sharpness in the image

  • flares/weird reflections



Add to that, a front lens element is a lot stronger than most people realize it and a lot harder to scratch than most people realize too. Unless you will be shooting in an environment where you need a filter to seal the lens or where you know you will have dirt on your lens (say a beach/desert with sand, a rally event where mud may hit your lens) it is not advisable to use a filter for "protection" unless you desire the effect of the filter.


A broken filter may also scratch your lens - which leads to the question whether they really offer protection (they shatter first but the shards could damage the lens).


If you are worried about the "odd bump", a lens hood is the better option.


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