Lens Filters: Thread Size, Polarizers and ND

Thread size: finding the number that fits your lens

Screw-in filters match the lens by thread diameter in millimetres, such as 52, 58, 67, 77 or 82 mm. The number is printed on the lens barrel or front cap after the diameter symbol. A filter with the wrong thread simply will not mount. If you own lenses with different threads, choose filters for the largest and use step-up rings on the others. Square or rectangular systems use a holder and adapter ring instead, which lets one filter serve many lenses.

UV, circular polarizer or ND: what each filter does

A UV or clear protection filter keeps scratches and fingerprints off the front element and has little optical effect on digital sensors. A circular polarizer cuts reflections on water and glass and deepens blue skies; choose circular, not linear, for autofocus and metering to work. Neutral density filters darken the scene evenly for slow shutter speeds. Coatings reduce flare, and thin frames avoid vignetting on wide lenses; stacking several filters raises both risks.

Questions about Lens Filters: Thread Size, Polarizers and ND

Do I need a UV filter on a digital camera?

Not for image quality: sensors already block most UV. Many photographers fit a clear filter to protect the front glass, but a poor one can add flare or ghosting, so use a good coated filter or none.

Why is my polarizer making the sky uneven?

On wide lenses the polarizing effect varies across the frame, so skies can look darker in one area. It is strongest at about 90 degrees to the sun. Use a longer focal length, or skip the polarizer for very wide shots.

What do ND numbers like ND8 or ND 1000 mean?

ND8 cuts three stops of light, and ND 1000 cuts ten, about a thousandfold. Higher strengths allow long exposures in daylight to blur water or clouds. Choose by the shutter speed you want, and consider a variable ND for flexibility.