Photographic lens filters play an essential role in enhancing your images and protecting your lens from abrasions. This guide introduces the basics and explores the three most common types: polarizers, neutral density filters, and UV/protection filters. Learn which filters can make a significant difference in your photography and which ones might not justify the cost. Read on to find out more.
What are photographic lens filters?
Photographic filters are accessories designed to modify the light entering a camera. Each type of filter serves a specific purpose, such as reducing glare and reflections, enhancing contrast, altering colours, balancing exposure, and more. Understanding the functions of various filters and incorporating them into your work can elevate your photography in ways that editing alone cannot achieve.
Attaching Filters to Lenses
Lens filters come in various shapes and form factors, depending on how they are attached to the lens. The four main form factors are circular screw-on filters, square and rectangular filters used with filter holders, drop-in filters, and gel filters.
Circular Screw-on Lens Filters
The most common type of lens filter is the circular screw-on filter because it is easy to use, commonly available, and requires no additional hardware for compatibility. These filters attach to the front of a lens using screw threads and come in various sizes to fit different lens diameters. The filter thread size is measured in millimetres and is typically indicated on the front of the lens with the diameter symbol (⌀) as a prefix.
Some lens filters have matching threads on their front side, allowing additional filters or accessories to be attached. This practice is known as ‘filter stacking.’ While stacking filters can be useful for achieving specific effects, be cautious not to overdo it. Using too many filters can degrade image quality by reducing contrast and introducing glare or vignetting.
Stepping Rings for Screw-on Lens Filters
Quality filters can be expensive, so rather than purchasing multiple sizes, consider using step-up rings to adapt larger filters to lenses with smaller thread diameters. For instance, a 77–82mm step-up ring allows you to attach an 82mm filter to a lens with 77mm threading. Step-down rings, which enable you to connect filters to lenses with larger threading, are less common. However, I don’t recommend using step-down rings, as they can cause vignetting.
Drop-in and Gel Filters
For long telephoto lenses, screw-in filters can be impractical due to their large front elements. These lenses often feature a drop-in slot for inserting small circular filters. On the other hand, ultra-wide-angle lenses with protruding front elements may have a rear slot for gel filters. These gel filters can be challenging to work with, as they are flimsy and need to be cut to size.
Drop-in Filter Mount Adapters
The Canon Mount Adapter EF-EOS R with Drop-In Filter° lets photographers use their EF and EF‑S lenses on EOS R series cameras while incorporating a drop-in filter. This design is useful for photographers transitioning from EF to EOS R mirrorless systems, allowing seamless use of existing lenses. This design is especially useful for lenses without front filter threads, like ultra-wide or specialty lenses. It also reduces the need to own and carry multiple adapters for lenses with different thread diameters, as a single filter can be used with any lens mounted to the adapter. Canon and third-party manufacturers offer a range of compatible filters for this system, including variable ND filters, circular polarizers, and clear protective filters, providing versatility for different shooting needs.
Filter Holders for Square and Rectangular Lens Filters
Filter holders offer a practical alternative to owning multiple screw-on filters for different lens sizes. Filter holders attach to a lens’s front and let photographers insert square or rectangular sheets of glass or resin to produce the desired effect. They reduce overall cost and bulk in a photographer’s kit, making them a versatile choice. You can rotate or shift these filters to control gradient transitions, align polarizers, or achieve other creative effects.
Circular Polarizing Filters
The first type of filter I’d like to introduce is my favourite: the polarizing filter. It is an indispensable part of any photographer’s kit due to its ability to create incredible contrast and colour saturation effects. The front portion of a polarizing filter rotates freely, allowing you to control the polarizing effect.
Polarizers work by allowing light oscillating in a specific direction to pass through while progressively filtering out light oscillating in other directions. For instance, light oscillating vertically will pass through a vertically aligned polarizer, while horizontally oscillating light will not. Light oscillating at an angle between vertical and horizontal will pass through at reduced intensity.
This produces several beneficial effects for practical photography. When shooting outdoors, especially on sunny days, you might notice harsh reflections on certain surfaces that can compromise your shot. A polarizing filter can be highly effective in these situations.
Polarizing filters reduce glare and reflections from non-metallic surfaces such as water, glass, wet or shiny surfaces, foliage, skin, and hair. By minimizing glare and shininess, they help colours appear more vibrant.
Pass your cursor over the photo below to see the effect of a polarizing filter on reflections in the glass.
Additionally, polarizing filters can have a significant impact on the appearance of the sky in your photos. They can darken the sky to a richer blue and reduce atmospheric haze, emphasizing the contrast between the sky and clouds.
Pass your cursor over the photo below to see how a polarizing filter affects the sky.
For landscape photography, keep in mind that maximum polarization occurs when the lens is positioned 90° from the Sun. The effect diminishes as you point the lens toward or away from the Sun, which can lead to uneven sky brightness when using wide-angle lenses. The glare and reflection reduction achieved by polarizing filters cannot be replicated in post-processing, making them invaluable tools.
Neutral Density (ND) Filters
ND filters are designed to reduce light intensity without affecting colour balance, allowing photographers to use slower shutter speeds for motion blur or larger apertures for shallow depth of field in bright conditions.
Long Exposures with ND Filters
Imagine photographing a beautiful fountain on a sunny day and wanting to create a smooth, silky appearance by blurring the motion of the water with a long exposure. By attaching an ND filter to your lens, you can significantly reduce the amount of light entering the camera, enabling you to use a slow shutter speed to achieve this effect without being limited by your aperture settings. It’s important to note that daytime motion blur effects achieved with ND filters cannot be replicated in post-production.
Shallow Depth of Field and ND Filters
ND filters are also useful when prioritizing aperture, such as when capturing a portrait with a large aperture to achieve a shallow depth of field in bright daylight. An ND filter allows you to use the widest aperture while remaining within your camera’s shutter speed limits.
ND Filter Strength Explained
The strength of an ND filter is determined by the amount of light it blocks. Manufacturers typically express ND filter strength using optical density, filter factor, and stop-reduction. The optical density is often stated in the filter’s name, while the light reduction in stops or the filter factor is usually included in the product description. (If all these mentions of ‘stops’ have you confused, check out my guide to what a stop in photography is.)
Optical density increases in increments of 0.3, with each increment representing a 1‑stop reduction in light. For instance, an optical density of 0.3 blocks 1‑stop of light, 0.6 blocks 2 stops, and so on. The filter factor indicates the fraction of light the ND filter allows to pass through, represented by the denominator. For example, an ND2 allows 1/2 of the light to pass through, an ND4 allows 1/4, an ND8 allows 1/8, and so forth.
ND Filters in Videography
Suppose you’re learning photography as a stepping stone to videography. In that case, it’s essential to understand the importance of an ND filter for outdoor scenes. Cinematographers use ND filters in daylight to achieve a shallow depth of field and cinematic motion blur, following the 180° shutter angle rule. In photographic terms, this convention means setting your shutter speed to the inverse of double the frame rate. For example, for a scene shot at 24 frames per second, the shutter speed is typically set to 1/48 s. Due to this convention, the shutter speed is relatively fixed, which limits exposure adjustments to the aperture and the use of neutral density (ND) filters. Since film scenes usually maintain consistent aperture settings throughout for creative reasons, exposure in bright conditions is often balanced using ND filters. Without them, the small apertures required to counteract the relatively slow shutter speed can diminish focus isolation and image quality due to diffraction. Variable ND filters (VNDs) simplify this process by offering a single filter capable of multiple light reduction levels.
Variable ND Filters
Variable ND filters offer casual photographers and videographers flexibility by providing a continuous range of light reduction within a single filter. They are made of two polarizing filters that rotate relative to each other. Turning the front ring adjusts the filter strength from minimum to maximum light reduction.
However, it’s important to note that variable ND filters aren’t a perfect substitute for dedicated fixed-strength ND filters. Their design can introduce undesirable effects to your photos, such as cross-hatch patterns in out-of-focus highlights, significant shifts in colour balance, and uneven cross-pattern darkening across the image.
UV and Protection Filters
Unlike the pronounced effects of polarizing and ND filters, UV filters have a more subtle impact. Film photographers traditionally used them to reduce atmospheric haze and prevent UV-induced contrast loss or colour shifts. However, since modern camera sensors are less sensitive to UV light than film, UV filters are now primarily marketed as lens protection filters.
When Protection Filters Are Helpful
Photography can take place in various environments, some of which feature rough conditions that can be hard on equipment. Ironically, these challenging environments often produce some of the world’s most compelling photos.
Protection filters are recommended when working in dusty, sandy, or wet environments, or in any situation that exposes your equipment to abrasive or penetrating substances. Sandy areas pose a particular risk, as a single grain of sand can cause damage when cleaning the lens. It is far cheaper and easier to replace a protection filter than to repair a scratched lens.
Lens caps offer excellent protection when lenses are not in use, but let’s be honest—we’ve all tried to take a photo with the lens cap still on. To avoid this hassle, some professional photographers skip lens caps altogether and rely solely on protection filters. Just remember not to leave your lens facing the Sun for prolonged periods!
Keep in mind that filters aren’t magical; while they can protect against moisture and dirt, they are unlikely to save your lens from forceful impacts.
When Protection Filters Are Useless
While protection filters have merit in certain conditions, they are largely unnecessary for casual photographers under normal shooting conditions.
Since I started teaching photography lessons in Toronto, I’ve noticed that many beginners come to lessons with protection filters on their lenses, often without realizing it or understanding their purpose. Unless the lens was borrowed or handed down, my suspicions often turn to persuasive camera store salespeople rather than a genuine need for lens protection.
Ironically, the low-quality protection filters that many people buy or inherit with used lenses are more likely to negatively impact image quality than a scratch. Higher-quality filters often feature effective anti-reflective coatings that are less likely to degrade image quality with glare and ghosting, but most new photographers use the cheap filters that come bundled with camera kits or upsold by camera stores.
Sometimes, people go to great lengths to keep their gear in pristine condition. However, as the saying goes, lenses are tools, not jewels, and it’s okay for them to show signs of use. The first scratch is always the most painful, but each mark tells the story of the moments you captured.
Another good reason to avoid using clear filters in conditions where they aren’t necessary is the risk of damage. The internet is full of stories and pleas for help from photographers who’ve dropped or knocked their filtered lenses, bending the threading and making it impossible to remove the cracked filter. While a warped filter thread won’t directly ruin your photos, you’re unlikely to feel like taking pictures if a shattered filter is still stuck on your lens.
Ultimately, if your lens needs protection from abrasive particles and harsh environments, invest in a high-quality clear filter from a reputable brand. Otherwise, save your money. And lastly, remember that lenses are automatically protected whenever you use polarizing or ND filters.
Conclusion
Photographic lens filters can help improve your images by enhancing colours, managing exposure, or protecting your lenses in harsh environments. Incorporating the right filters into your photography toolkit can make a noticeable difference in the quality and impact of your photos.