UV or not to UV

UV or no UV

The topic of whether you should use a UV filter on your lens, or not, has been hotly debated since I can remember. Even amongst professionals opinion is split and advice mixed. To my knowledge, I don’t think enough scientific tests have been conducted to prove that a UV filter is a good or bad thing.

So what is a UV filter and what is its purpose?

It is an ‘Ultra Violet’ filter that screws onto the end of your lens.  Its intended purpose is based on two main arguments:

1.    It protects the end of the lens from scratches and dust.
2.   It blocks out ultra violet light and removes a blue cast on images.

UV Filter

UV Filter

To be honest, I never use UV filters and don’t believe they are a good purchase.  Retailers sell them, almost by default, to any unsuspecting buyer purchasing a lens; this is usually based on the fear factor that you need this to protect that nice shiny new lens you are about to buy. 
I think it’s the same fear marketing you get when you purchase an electrical item from a store and then get told you need to spend another chunk of cash on extended warranties or insurance to protect it.

So let’s go through the main arguments for, and against, the use of a UV filter.Arguments for a UV filter

1.    Lens Protection

“I might drop my camera, scratch the lens or want to keep the lens surface free of dust and dirt”.  

I can assure you that if you drop your camera then the UV filter is probably the least of your worries. Dropping your camera is more likely to do greater damage to the lens barrel than the lens glass. If the UV filter is scratched or broken in the process then it’s very likely that you will have damaged the lens glass too as the tiny shards of glass go onto your lens element.  

You also have the near impossible task of trying to remove the UV filter from the lens that is now permanently jammed because it is slightly buckled.  

Using the lens hood that came with the lens is a good defence for the lens glass: the lens hood protrudes in front of the lens glass so is the first area of contact should you knock or drop the lens.
 
If you are using a UV filter because it keeps the lens glass clean then I don’t understand the difference between having to clean one over the other.  Surely a clean surface, whether it is the UV filter, or lens, is a must either way?

2.    Blocks out ultra violet light and removes blue colour cast

In modern digital cameras this is a bogus argument. In the days of film cameras the film was extremely sensitive to UV light. The sensors in digital cameras are largely insensitive to UV light so the filter will have very little or no effect.

Arguments against a UV filter

1.    Quality of UV glass

In my own experience I have seen a loss of image quality by using a UV filter but there are two factors that need to be considered. First, the quality of the UV filter itself. If you buy the cheaper UV filters, it is almost guaranteed that the quality of the UV glass is inferior to the quality of the lens glass. Secondly when using a higher quality UV filter (B+W, Tiffen etc) the difference in picture quality is marginal; it therefore becomes a question of whether you want to sacrifice any quality, however small, for peace of mind that you have ‘lens protection’.

2.    Flare & ghost images

Cheaper UV filters and bright light are often the cause of lens flare. Flare and ghosting are caused by unwanted and scattered light bouncing off the glass surfaces. The addition of a UV filter will increase the likelihood of this in certain shooting conditions. It’s another marginal factor and only a real consideration on cheaper UV filters.

3.    Loss of light

There doesn’t seem to be any real evidence to support this claim or refute it.  A good quality UV filter should not reduce the quality or quantity of light hitting the cameras sensor. However it should be acknowledged that lens are designed and coated to work optimally without the use of filters. However, sometimes it is essential to use filters, as with polarisers and density filters, to get the exposure and effects you want. My approach is to use as few as possible which, whilst again marginal, reduces any derogation in light.

4.    Loss of resolution

This is simply down to the quality of the filter you buy. Cheaper UV filters may cause some loss of resolution when you are at telephoto focal lengths on the account on being optically flat. The biggest culprit for loss of resolution is a dirty filter. Dirt and dust or smears on a UV are not invisible just because your lens element is free of them – the simple answer is to keep it clean.

5.    Vignetting at wider angle focal lengths

Additional circular filters in front of the lens may cause vignetting (where you will see the black corners in the image frame) when you stack one filter on top of another. As more filters are stacked, the lens at wider angle focal lengths records the edges of the filters in front of it. If you are using a UV filter, polariser, ND and or GND filter then you will not be able to shoot with your lens at 10-24mm focal length without the corners of the photo vignetting.

Conclusion

The arguments for and against the use of UV filters will no doubt be controversial and rage on amongst photographers. For me, I take the simple view that I do not want to compromise any aspect of image quality, however small, and would rather take the small risk of a mishap over the reduction in quality on thousands of photos.  So I don’t use UV filters or recommend them for most people.

In ten years I have only scratched a lens element once – and remember, a scratch doesn’t necessarily mean a replacement.  Take a look at this:
https://www.flickr.com/photos/erictastad/sets/72157616647751423/

If, like me, you simply can’t live with a scratch, however small, then the cost of having a repair or replacement might not be as expensive as you think. Typically the cost to replace or repair a scratch is approximately 10-15% of the price of the lens.

If you want to find out whether your lens, or a lens you are buying has scratches and other issues then take a look at the flashlight test here.
http://www.kenrockwell.com/tech/flashlight-test.htm