Landscape Filters Quiz

A circular polarizing filter works by blocking polarized light reflecting off water, glass, and foliage, and by absorbing scattered blue light from the atmosphere at right angles to the sun. The result is richer colors, stronger sky contrast, and reduced surface glare.

Polarized light reflected from outdoor surfaces is maximally polarized at roughly 90 degrees from the light source. Positioning the subject at that angle to the sun and rotating the filter until reflections disappear produces the strongest polarizing effect.

An ND filter reduces the light entering the lens evenly across all colors, the way sunglasses do for eyes. That allows a slower shutter or a wider aperture in bright light without changing the scene's colors.

Silky water needs a shutter speed of about a second or longer, and in daylight that overexposes even at base ISO and a small aperture. A 6 stop ND cuts the light 64 times and a 10 stop about 1,000 times, allowing those long exposures. UV and clear filters barely reduce light at all.

A graduated ND filter is dark on one half and clear on the other, with a transition between them. Lining the dark half up with a bright sky lowers its brightness while leaving the foreground untouched, so both fit in one exposure. A neutral grad does not tint the image.

A variable ND is two polarizers stacked; rotating one changes how much light the pair blocks. Turned past its maximum strength, the polarization becomes uneven across a wide view and a dark X or cross pattern appears. Many variable NDs have hard stops to prevent it.

A reverse grad is darkest along its middle line and fades lighter toward the top. When the sun sits on the horizon, the brightest band of sky is just above the horizon, not at the top of the frame, so a reverse grad darkens exactly that band. A standard grad is darkest at its top edge instead.

ND numbers express the filter factor: ND8 lets through one eighth of the light. Each stop halves the light, and 8 is 2 times 2 times 2, so ND8 cuts three stops. ND2 is one stop and ND4 is two.

A step-up ring screws into a lens with a smaller filter thread and offers a larger thread on the front, so one set of large filters can fit several lenses. Going the other way, a smaller filter on a larger lens, needs a step-down ring and usually causes vignetting.

Each filter adds depth in front of the lens, and with two stacked, the extra rims can intrude into the edge of the field of view, especially on wide-angle lenses. That shows as dark corners, which is vignetting. Extra glass also tends to add flare and reduce sharpness, not improve it.