Camera Filters Explained: UV, Polarizer, ND and More

Walk into the filter aisle and it’s easy to feel like you need a drawer full of glass to take a good photo. You don’t. Most of the filters on the shelf do little or nothing on a modern digital camera, but a couple of them do something you genuinely cannot fake later on a computer. This guide sorts the useful from the gimmicky — what a UV, polarizer and neutral density filter each actually do, when each one helps, and the ones you can safely skip — starting with the one number you need to know before you buy anything.

First, get the thread size right

Before any of this matters, a filter has to physically fit your lens, and that comes down to the filter thread size— the diameter of the front of the lens measured in millimeters. Look on the lens for a small number followed by “mm”, usually printed next to a circle symbol that looks like a zero with a line through it. It’s often on the front ring around the glass, sometimes on the inside of the lens cap. Common sizes run from around 49mm on small lenses up to 67mm, 72mm and 77mm on larger ones. A 58mm filter only screws onto a 58mm thread, so this number is the first thing to check.

If you own several lenses with different thread sizes, you don’t need a separate filter for each. A cheap accessory called a step-up ring adapts a larger filter to a smaller lens — buy your good filters in the biggest thread size you own, then use step-up rings to fit them onto the smaller lenses. One quality polarizer and one ND can serve your whole kit that way, which is far better value than buying mediocre filters in every size.

UV and clear protection filters

The UV filter is the one most people are told to buy first, and it’s the one that does the least. On old film, ultraviolet light could add a haze, so a UV filter helped. Digital sensors simply aren’t sensitive to UV in the same way, so on a modern camera a UV filter has almost no effect on the image. Its real value today is physical protection: a thin piece of glass over the front element that takes the dust, sand, sea spray, rain and stray fingerprints instead of your expensive lens coating.

That protection is a fair reason to use one — but only if it’s good glass. A cheap filter puts a low-quality layer in front of a high-quality lens, and it can introduce flarewhen shooting toward the sun or a soft haze that robs fine detail. So the honest advice is simple: either buy a good one and leave it on for protection, or skip it entirely and rely on a lens hood and the lens cap. There’s no middle ground where a bargain-bin UV filter helps your photos.

The circular polarizer: the one you can’t fake

If you buy only one filter, make it a circular polarizer (CPL). It mounts in two parts so the front ring rotates, and as you turn it you watch the effect change through the viewfinder. What it does is cut glare and reflections: the shine off water so you can see into it, the reflection on a shop window or a car, and the sheen on wet rocks and leaves that washes out their color. Remove that glare and colors look richer and more saturated, which is why foliage and landscapes get so much punchier through a polarizer.

It also deepens a pale blue sky, adding contrast between the sky and the clouds. The crucial point is that this effect is optical — it genuinely cannot be recreated in editing. Software can boost color, but it can’t remove a reflection or glare that was already recorded in the file. There are two things to know: a polarizer costs you roughly one to two stops of light, so you shoot at a higher ISO or slower shutter, and it works best when you’re aimed about 90 degrees from the sun. It’s a favorite for anyone shooting outdoors — see our how to photograph landscapes guide for exactly where it earns its keep.

Neutral density: sunglasses for the lens

A neutral density (ND) filter is a piece of solid gray glass that does one thing: it blocks light evenly without changing color. Think of it as sunglasses for the lens. Why block light on purpose? Because it lets you use settings you otherwise couldn’t in bright conditions. For stills, an ND lets you slow the shutter to a long exposure in daylight— the technique behind silky, smoothed-out water and clouds blurred into streaks. Those long exposures need the camera dead still, which is where a solid tripod becomes essential.

For video the ND is arguably even more important. Natural-looking footage comes from keeping the shutter speed at about double the frame rate — the 180-degree shutter rule— and many shooters also want a wide aperture for a shallow, cinematic background. In bright daylight both of those choices flood the sensor with light and the footage blows out. An ND cuts the light so you can keep the shutter and aperture you want without overexposing, which is why serious video shooters treat it as a permanent part of the kit. Our best camera settings for video guide explains the shutter rule in full, and matching an ND to your glass starts with checking thread sizes across your lenses for video.

Variable ND: convenient, with a catch

A variable ND is a clever design that lets you dial the darkness up and down by rotating the filter, covering a whole range of strengths in one piece of glass instead of carrying several fixed ones. For run-and-gun video, where the light keeps changing, that convenience is hard to beat. The catch is in how it works: at the strongest settings a variable ND can produce an uneven, X-shaped dark band across the frame, and cheaper ones can also shift the colorof the image toward a tint. Stick to a good-quality one and keep it away from the extreme end of its range and it works beautifully; buy the cheapest option and you’ll fight those flaws.

Graduated ND and the effect filters

A graduated NDis dark across the top and clear across the bottom, with a smooth transition in the middle. The idea is to hold back a bright sky while leaving a darker foreground untouched, so the whole scene sits within the camera’s range. It was once essential for landscapes, but bracketing— taking several frames at different exposures and blending them — and the wide latitude of a RAW filehave largely replaced it for most shooters. It still has fans, especially for getting the shot right in a single frame, but it’s no longer a must-have.

Then there are the special-effect and star filters— the ones that turn every highlight into a sparkle, add soft glows, or split the image. These are mostly gimmicks. The effects are heavy-handed, hard to control, and easy to overdo, and anything you might want from them you can add with far more control later in editing. Spend the money on a good polarizer or ND instead.

Buy quality, and match the thread

The theme running through all of this is that a filter sits in front of your most important piece of glass, so a bad one drags down everything behind it. It’s better to own one good polarizer and one good NDthan a bag full of cheap filters, because poor glass adds flare, softness and color casts you’ll never fully edit out. Before you buy, confirm the thread size printed on your lens, buy in the largest size you own, and use step-up rings to share those filters across the rest of your lenses.

The short version

Check the millimeter thread size on your lens first, and use a step-up ring so one filter can serve several lenses. A UV or clear filter does little for image quality on digital — its only real job is protecting the front glass, so buy a good one or skip it. A circular polarizer cuts glare and reflections and deepens a blue sky in a way you truly can’t recreate in editing, at the cost of a stop or two of light. A neutral density filter is sunglasses for the lens, unlocking long exposures in daylight and letting video shooters hold the 180-degree shutter rule. Variable ND buys convenience with the risk of uneven darkening, graduated ND has mostly given way to bracketing and RAW, and star and special-effect filters are gimmicks. Spend on quality glass, match the thread, and skip the rest.