by David Tong
One common advice we hear from photographers is to immediately purchase a skylight or UV filter to protect our lenses. The premise is simple, a clear filter is a cheaper replacement than a damaged front lens element. Most UV filters are bought mainly for protective purposes only these days as UV doesn’t seem to affect digital images anyway.
There are, however, those who will insist that adding a piece of glass in front of a precision-engineered lens will alter the light rays no matter how good the filter is. In addition, quite a number of photographers will also note that filters will induce flare because the lens’ front element is designed to reflect a certain wavelength of light and the filter will actually bounce it back to the lens, and so on.
My philosophy with UV filters is simple, if the glass is large enough and protrudes enough, I’ll use a filter. I’m a rough user and unless it’s a macro lens where the element is deeply recessed, or a cheap lens, or a lens that I’ll never use without a deep lens hood (like telephotos), I prefer to use a filter due to my careless nature.
So today, I tried a simple test on a Canon EF 24-105 f/4L IS USM lens shooting still subjects with a relatively large light-source close to the lens using different apertures with both filter-on, and filter-off. The filter used is an entry level Hoya Standard UV filter.
I’ll let you draw your own conclusion based on the gallery below. You can see the EXIF by clicking on the images. They are sorted by Filter On, then Filter Off with similar exposures.
My conclusion, at least for this lens/filter combination, is that the differences can be seen, especially when scrutinized at 100%, but hardly visible enough to say that the difference is pronounced. This could simply be a lens issue, though. I’m pretty sure that different lenses will behave differently, as well as different filters may produce different results as well.
In this case, the image quality differences are minimal, if not negligible. Some images at wide-angle have a little sharpness loss with the filter on, but flare differences are minimal.
A filter may protect the front element from day-to-day scuffs and smudges, it’ll also save the front element from microscopic rub marks from brushes and lens cloths, but in some cases, a filter may cause more damage compared to a more direct impact to the lens. Whether a filter is worth it or not, it’s up to you to decide.
What are your thoughts? Feel free to post.