One of the most discussed, debated and often heated arguments on photography websites and forums revolves around the use, or not, of protective filters on lenses. On one side of the camp are those that believe filters are useful and beneficial additions to expensive lenses and do not affect image quality and, on the other side are those that believe any filter degrades the quality of any lens. To be up front, I have always used high quality filters on all of my lenses from day one and believe that the benefits far outweigh any minor issues that they may cause. There’s a reason for that and I’m going to explain why. While at the end of the day you might not agree with me, I will at least have provided my side of the argument for the use of filters.
One of the most often stated reason for not using a filter goes along the lines of ‘Why put a cheap piece of glass’ (often referred to in prehistory as a Coke or milk bottle, as they came in glass bottles) in front of your expensive lens?’ Well, if you use a ‘cheap piece of glass’ on your lens, then it’s probably not going to provide acceptable results unless you’re after a specific effect, as has been the order of the day for generations. Photographers used to put Vaseline on their filters, stretch stockings over lenses and use all manner of ideas to get creative effects; however, the latter isn’t so necessary nowadays with available software that, to a large extent, can emulate most of these effects. That said, there is no reason why you should use a ‘cheap piece of glass’ on your lens. There are numerous filters available that use the highest quality optical glass with the best possible coatings, such that they equal or better those found on some lenses. The inference that every filter is just a ‘cheap piece of glass’ is completely erroneous and certainly shows a lack of understanding on the part of the proponent.
Another major fallacy when it comes to protective filters is the belief that photographers use them to protect the front element of the lens from impact. That is usually the very last reason, if one at all, for using a filter. A lens hood provides far more impact protection than anything else, as well as the benefit of flare reduction (I’m constantly amazed at how many photographers never use a lens hood, or simply keep it reversed on the lens). What protective filters do is protect the front element from the hazards of being out in the open, in such places as a beach with flying sand or a boat subjected to salt spray; outback locations with abrasive, clinging, dust; fields or forests with mud, sap and any manner of sticky crud; or kids parties with numerous obnoxious things intent on smearing your lens. For fair weather and/or benign environment photographers, feel free to not use filters, but for those that venture regularly to the wild side (not that one), filters are often essential.
It’s also interesting that just about every manufacturer offers protective filters for their lenses (Nikon doing even more so lately), or others have these supposedly built-in as a form of ‘sacrificial’ front element where front threads are not provided, but this is rapidly changing. These are typically fast telephoto and super-telephoto lenses where the front element is often very large and producing screw-in filters can be problematic and they will be very expensive as well. One of my lenses came with a factory filter supplied and it’s the largest filter by size of any of my others (105mm), a fairly uncommon size at that. But when a lens manufacturer supplies you with a filter, you have to suspect that it’s been done with a purpose and taking into account the full optical path, so as not to risk affecting the quality of the lens. And it doesn’t matter whether the filter goes in the front or the rear of the lens. But if the rear filter gets damaged, dirty or removed, it will affect the image quality.
The somewhat amusing thing is that out of all filters, neutral density and polarising filters are the most common ones in just about any keen photographer’s camera bag, yet these filters will most likely cause the most image degradation, especially colour casts (some are absolutely terrible). Yet those who decry clear filters, seem to have no issues with what the former filters can do to image quality, suggesting that they are prepared to accept the consequences. Other filters that some use are graduated neutral density filters that are positioned over the front of the lens in a holder and many of these are usually made from optical plastic, by no means the same quality as optical glass. But, once again, many are quite prepared to use these and not be concerned with image degradation.
In all the years that I’ve been taking photographs and using filters, I’ve never found filters to degrade the results in any noticeable way; however, filters have saved the front element of my lenses numerous times when out in the bush. The worst was when I somehow got a large blob of very sticky sap just off-centre of the filter and the only way to remove it was to soak the filter in river water, soften and then carefully remove the blob. Had this blob landed on the front lens element, I’m not sure that I would have found it so easy to remove and it may have done severe damage to the lens coating by the time I got home to a more controlled environment (all those that leave bird droppings on their cars for ages take note). That’s not to say this is something that happens every day, but I recently noticed that the filter on one of my oft used lenses is starting to show a lot of minute scratches, pits and marks over its surface. While even severe marks may never show up in the final image, it doesn’t mean that such won’t invoke other issues (they become tiny collection pits for all manner of gunk) and I’d much rather that these marks appear on a filter and not the lens itself.
So at the end of the day, my view is that high quality filters can only benefit, rather than detract from your photography. I’m sure that people can provide examples of where they have encountered issues, such as flare, but I will always wonder what sort of filter they have used and whether they were using a lens hood. So that’s my personal observation on filters and I was pondering whether to do some objective tests to put some of my thoughts into actual examples, until someone else did just that and confirmed my faith in the B&W MRC filters that I’ve been using for the last decade or so (I wish I could get them in Australia at the prices quoted for the 77mm size). So when it comes to filters, you have a choice of the Good, the Bad and the Ugly, so make a wise choice.