Lens Filters Explained: UV, ND, CPL and When to Use Each
By Camix | Published: 2026-10-16
Category: How-to Guides
A practical walkthrough of UV, ND and CPL filters, what each one actually does to your photo or video, and a simple order of operations for choosing and using them.
Quick answer
Use a UV filter as everyday front-element protection, a CPL when you need to cut glare or deepen a sky, and an ND when you need to slow the shutter or open the aperture in bright light. Match the filter to one job at a time, and buy the size that matches your lens thread rather than the size of the lens barrel.
Start with the filter size, not the filter type
Every filter screws into the thread at the front of the lens, and that thread is measured in millimetres. A 37mm filter fits a 37mm thread and nothing else, so check the number printed on the lens barrel or inside the front cap before you shop. Buying the wrong size is the single most common first mistake, and step-up rings only solve it in one direction.
If you own several lenses with different thread sizes, decide whether you want one filter per lens or a set of step-up rings that let a larger filter serve smaller lenses. A larger filter on a step-up ring can vignette on very wide lenses, so test at your widest focal length before committing.
Choose the filter type by the problem you are solving
UV filters are the simplest: they sit on the lens full time and take the knocks that would otherwise reach the front element. Their effect on image colour is minimal on modern digital sensors, so treat them as insurance rather than a creative tool.
A CPL, or circular polariser, removes polarised light from reflections on water, glass and foliage, and it deepens blue sky when you shoot at roughly 90 degrees to the sun. It costs you around one to two stops of light, and the effect changes as you rotate the ring, so it is a deliberate choice rather than a default.
An ND filter cuts the amount of light reaching the sensor without changing colour. Fixed NDs come in strengths like ND8 or ND64, while a variable ND lets you dial the strength across a range in one filter. ND is the tool for long exposures in daylight and for keeping a cinematic shutter speed in bright conditions.
Mount and check before every shoot
Screw the filter on gently until it is snug, not tight. Over-tightening makes removal difficult, especially in cold weather, and cross-threading damages the lens thread. Once mounted, look through the viewfinder or at the screen at your widest aperture to confirm there is no new vignetting in the corners.
Clean the filter before you leave rather than on location. Use a blower first, then a microfibre cloth, and avoid breathing on the glass in cold air because condensation can leave marks. A scratched or smeared filter is worse than no filter at all.
Step-by-step: choosing and using your first filters
- Measure your lens thread: Look for the diameter symbol followed by a number on the front of the lens barrel or the inside of the lens cap. Write it down for every lens you plan to filter. Checkpoint: if two lenses share a thread size, one filter can serve both.
- Buy protection first if you shoot in crowded or dusty places: A UV filter is the least intrusive choice because it stays on the lens and changes nothing about your exposure. Choose a coated version if you shoot towards the light. Checkpoint: remove it briefly and compare a backlit frame to see whether the filter adds flare.
- Add a CPL for landscape and reflective subjects: Rotate the ring while watching the sky or water until the glare drops and contrast peaks. Expect to lose about one to two stops of light and compensate with shutter speed or ISO. Checkpoint: polarising effect is strongest at 90 degrees to the sun and almost absent when shooting directly into or away from it.
- Add an ND for long exposures or bright-light video: Pick a fixed strength if you know your target shutter speed, or a variable ND if you need to adjust quickly between shots. Focus before you mount a strong ND, because dark glass makes autofocus struggle. Checkpoint: on a variable ND, watch for cross-shaped darkening at the strongest setting and back off until it clears.
- Stack only when you must: Combining a UV and a CPL is usually fine, but adding an ND on top of both increases the chance of vignetting and internal reflections. Use the fewest filters that solve the problem. Checkpoint: if you see a soft dark ring in the corners, remove one filter and reshoot.
- Store and clean them properly: Keep filters in a case rather than loose in a bag, and clean with a blower and microfibre cloth. Check the thread for grit before mounting. Next step: label the case with the thread size so you grab the right filter without guessing.
Filters worth considering
- K&F 37mm Classic Blue coat MCUV Lens Filter: K&F 37mm Classic Blue coat MCUV Lens Filter, catalog price USD 11.84, with 1 Year Warranty, free UK delivery and brand new stock. A low-cost way to protect a small-diameter lens such as a compact or kit lens without spending more than the lens is worth.
- K&F Concept 112mm MCUV Protection Filter with 28 Multi-Layer Coatings: K&F Concept 112mm MCUV Protection Filter with 28 multi-layer coatings, catalog price USD 46.90, with 1 Year Warranty, free UK delivery and brand new stock. A large-diameter protection filter suits wide lenses where a cheap uncoated filter would flare more noticeably.
- K&F Concept Nano-X ND8~128 Variable Fader 82mm Filter: K&F Concept Nano-X ND8~128 Variable Fader 82mm Filter, catalog price USD 65.10, with 1 Year Warranty, free UK delivery and brand new stock. One variable ND covers a wide range of light-cutting strengths, which is useful for video shooters who need to hold a fixed shutter speed outdoors.
