UV Filters - What You Need to Know

What is a UV filter? Do you need a UV filter? What does a UV filter do?

In this blog post we will answer all of these questions and more. We will discuss UV filters, what they do, and instances where a UV filter can be beneficial for photographers. If you'd rather watch our video covering the same information, check it out here on our YouTube channel.

First, let me explain what UV is and the differences between UV filters and other filters referred to as haze filters, clear filters, and skylight filters. UV light is a type of electromagnetic radiation and it is responsible for your tan (or burn) and appears to our eyes as a hazy sky. We cannot actually see UV light. It is out of the spectrum of visible light; however, UV light waves have a wavelength close to the size of air molecules so when UV light waves come through our atmosphere they “scatter” (the technical term is Rayleigh scatter).

This scattering is responsible for the blue color of the sky and the haze we see when we view a large volume of air like the wide open skies in a landscape. If you want to get more technical than this, there are many great scientific articles online that will give you all the details. For our purposes, you simply need to know that UV light shows up as hazy skies to our eyes.

A UV filter is used to block or minimize the UV light reaching your camera’s film or sensor thereby reducing the haze seen in a photo. Sometimes you will see them referred to as haze filters or UV haze filters, but they are not exactly the same thing. A UV filter may be clear (usually a protective UV), or in the case of stronger UV coatings may have a warm or amber tint. A haze filter may also have a colored tint to it. A haze filter will block or minimize the haze just like a UV filter. Another similar filter is a skylight filter. A skylight filter is a UV filter with a slight magenta color (or orange-pink) to warm up the sky and remove some of the blue. It will also block or minimize haze. A clear filter is simply a clear filter. It should have no color cast and in many cases will still block some of the UV light (but not always). A UV filter would theoretically do a better job of blocking UV than a clear filter. UV filters will often have a combination of letters or numbers that indicate the amount of UV blocking. At the bottom of this article is a table with some common designations and filter levels. Keep in mind that in the industry there is no universally agreed upon use of these letters and numbers so any manufacturer may use any designation they choose at any time.

UV filters (and the others mentioned here) were very useful back in the days of color film photography, especially in bright light and for landscape photography. Film was strongly affected by UV light and when taking landscape photos you exposed the film to lots of UV light waves. If a UV filter was not used, photographs had more haze and a stronger blue tint throughout. When a filter was used, it cut down on the UV hitting the film and reduced the hazy, overly blue tint of a landscape photo. Filters were also used to adjust white balance before digital white balance. Some of the filters mentioned above included a warm tint to help cancel out unwanted colors, in particular the excess blue in large expanses of sky.

In today’s digital cameras these filters will have little (if any) effect. Modern cameras have coatings or additional blocking on the sensor to exclude UV light and most cameras have a digital white balance function. In fact, today’s cameras are so good that not only will a UV filter do little to improve a photo, it might actually reduce quality.

This is where the debate begins! Should you use a UV filter or not? Why would you even want one if it won’t improve a photo? Legions of photographers are lined up on both sides of this argument and it is a Hatfield-McCoy type argument that will probably never be resolved.

Let’s address the pros to a UV filter and why you might want to use one.

Despite the fact that most cameras now have UV blocking on the sensor, UV light has different wavelengths, just like visible light, and some of those wavelengths may not be fully blocked from reaching the sensor. It is possible the haze reduction could be enhanced by a high end UV filter. The highest quality UV filters will give you statistics about the range of wavelengths and percent of light blocked. If you are a pro landscape photographer and do the research, there may be a filter that could improve upon the results with your given camera (depending on the quality and level of UV blocking in the specific camera you own).

Below are two sets of images. The first pair (left) is a set of promotional images from a filter manufacturer supposedly demonstrating the difference with and without a UV filter. The second set of images are test images I did with my Canon 5D with and without a UV filter. In both cases the "without filter" image is first. I personally prefer the without filter images from my Canon and I see no obvious improvement in terms of color or haziness with the filter in place.

A UV filter can be used to weather seal the front end of your lens and make it easier to clean. There are some unique circumstances where this “sealing” effect would be beneficial. If you spend large amounts of time photographing the ocean, ocean spray, and ocean waves, or do beach portrait photography, then a UV filter could protect the end of your lens from sand and water. If the salty sea spray or something oily gets on the end of the lens, a filter is easier to clean and your lens won’t be damaged over time from repeated cleanings. Repetitive and excessive cleaning of your lens can wear off special coatings over time as well as create a slow accumulation of micro scratches. If these happen to the lens, it could reduce image quality. If this happens to a filter, you can toss the filter and buy a new one.

Another reason many photographers choose to use a UV filter is to protect the lens from scratches or chips and breakage. By placing a UV filter on the end of the lens you would be providing an extra layer or barrier between the lens and the world. I place UV or clear filters on the end of lenses I use with my students. I once witnessed the filter save a lens when a student tripped and fell with the camera. The filter took the brunt of the hit and broke, but the lens and camera were fine. For my purposes, it offers some peace of mind. It also means I don’t have to supply the cameras with lens caps that ultimately get lost or misplaced. The filter acts like a lens cap instead.

So as you have learned, two of the three reasons for having a UV filter actually have nothing to do with UV filtering at all. In addition, if you work in studio nearly 100% of the time, then you would never need one for UV light or for walk-around protection.

Why are some photographers so adamantly opposed to the use of UV filters then? If you want to use it for protecting your lens, then why not just do so?

Those in the anti-UV filter camp strongly believe that the added piece of glass means poorer image quality. Theoretically, the more glass elements, the less clear the image should be. Each piece of glass lets light in, but not at 100%. Some of the light is bounced back and not always directly away. When light bounces around in the lens or between glass elements it can result in ghosting or lens flares (see image below). A lens is a scientifically developed optical system with all of the elements designed to work together for sharpness and color accuracy in photographic images. If you add a filter, especially one with poor optical characteristics, then your lens may not be able to perform at its best and you end up with compromised image quality.

If you select and use a pro-quality UV filter that has been engineered to reduce defects, distortion, or aberration, then theoretically any loss of color, quality or sharpness would be at such a pixel level it would be almost impossible to tell when viewing photos at their full size. However, what is often the case, is that filters (even expensive ones) are not manufactured to the specifications that would make them truly flat or of an optical grade (variation of a few hundred nanometers or less). Instead many filters are only flat to a deviance of about 2000 nanometers. That is significantly “wavy” by optical standards and this results in distortion as light passes through. The waviness you might observe will likely be greater and greater with cheaper and cheaper filters (although I am sure there are exceptions). The filters that are supplied with camera kits usually fall into the cheapest of specimens and should never, I repeat never, be used if you are serious about image quality.

I believe that for your average hobby photographer a moderately priced UV filter will not ruin your image quality in a discernible way. Your camera lenses already have between nine and fifteen glass elements on average. Adding one more layer of UV filter glass is not going to ruin birthday party photos or your weekend photo walk pictures. That being said, you still do not want to use the ones that come with a camera kit. At the end of this post we will give you some buying tips.

The strongest argument by far against the use of UV filters is the issue of flares. In certain situations (usually bright lighting and with no lens hood in place or at night like the example below) and at certain angles you might experience ghosting or flares in your images. Having a multi-coated filter may prevent some flaring, but it can still happen.

There are workarounds to the problems UV filters can cause. As I said before, get a good quality UV filter and get one that has multi-coating. That will prevent some of the quality issues. Additionally, using a lens hood can block some of the light angles that will cause flares and other aberrations. The lens hood is another layer of protection for the end of your lens as well. When using filters, choose the right filter for the job and as a general rule never stack filters (although with advanced use there are times you will need to stack them). Stacking filters can compound the issue of more glass/less quality and more bouncing light rays/more flares. For each scene you photograph you should determine whether the filter(s) will be a benefit or not. For example, a UV filter won’t help at all if you are taking a close up of a flower or working in a studio setting, but a stronger UV filter might benefit a landscape photo. You can leave the UV filter on as you walk and move around. Once you get set up for the shot, you can remove the filter when you don’t need it. Then replace the filter before you move to a new location.

If you decide you want to purchase a UV filter, here are a few buying tips. UV filters are available in a circular screw on version that goes on the end of your lens. These are mainly the types I am referring to when discussing filters in this article. There are also filter holders that will hold filters of different types. The holder is added to the end of the lens or between the camera body and the lens. Filters can then be dropped in or removed as needed. These filters may still be round, or they may be square or rectangular (see image below). Most of the drawbacks to using UV filters will apply to filters/filter holders, but some of the benefits, such as lens weather sealing, may not apply.

When purchasing the circular screw on type of filter you will need your lens size. Each lens in your collection may require a different size. For example, my 50mm lens requires a 49mm threaded screw on filter while my 17-40mm requires a 77mm size. The lens filter size can be found on the end of the lens or on the lens cap cover, usually marked with a letter o or zero with a slash through it then the number size (and sometimes followed by mm). Do not confuse the lens filter size with the lens focal length. If you want to purchase just one UV filter to switch out between all of your lenses, then I would recommend you purchase the largest size UV filter and a set of step down rings so you can size it to other lenses.

Lastly, get a good quality filter with high quality optics made of real glass or resin. You will need to do your research into the chemical composition of the glass and how it was made. Thinner glass is better than thicker glass. Impurities in the glass will affect image quality. For example, glass with a higher iron content may have a green tint, whereas “water white” glass has less iron and is more optically pure (better light transmission and no tint). “Schott” glass is a fine optical glass, like the glass used for Zeiss lenses, so filters made with it will be better but also more expensive. Purchase a filter with multi-coatings that have been shown to reduce flares and give optimal colors. Do not get polyester or plastic filters.

The outer retaining ring should consist of metal including the threads. An outer retaining ring of aluminum is cheaper and more likely to dent, therefore brass retaining rings are preferable, but they are more expensive. Do not get filters with plastic rings.

Keep in mind that many manufacturers use “pro” in their item names and there is no set standard for the use of that term. The filter may be pro level or it may not be. Also be aware that Amazon and eBay are flooded with knock off filters, so even if you think you are buying a name brand you may get a fake. I recommend you purchase directly from the manufacturer or B&H Photo, Adorama, or Best Buy to make sure you get the real deal. In the photos below, a sign that the one on the left is a fake is the uneven font compared to the real brand item on the right with nice even text. This is just one possible way to detect a fake filter.

So what's the takeaway?

Whether you choose to use a UV filter is mostly a matter of personal choice and how you weigh the pros and cons to their use. There are really no right or wrong answers (although die-hard believers on one side of the debate or the other might disagree). I personally use a protective UV on my lenses and remove it when it might cause an issue. If you'd like help choosing a quality UV filter, we can assist you. Just get in touch with us on social media on our Twitter page @focusedcamera or send us an email at myfocusedcamera@gmail.com and we will be happy to help!