When to Use Each Filter

You now know what each filter does in isolation. This lesson is about judgment: in a real situation, on a real Bologna street, which filter earns its place on the lens, and which should stay in your pocket. Filters are tools, not decorations. The mark of a thoughtful photographer is restraint. Use the comparison tool on this page to see each effect, then take this decision-making into the street.

UV / Haze: the default of doing nothing special

Keep the UV filter on as protection most of the time. In dust, rain, or the gritty spray of a Bologna downpour, it is your sacrificial front element. But take it off in tricky backlight. When you shoot toward the sun or a bright light source, every extra layer of glass adds the risk of flare and ghosting, ugly reflections that wash out your contrast. A bare lens flares more predictably and often more beautifully. So: protection on by default, off when the light gets difficult.

CPL: your most powerful creative filter, and Bologna's best friend

The circular polarizer is the one that does things you cannot replicate in editing. Reach for it in these situations:

Wet cobblestones. This is the Bologna signature. After rain, the streets glare with reflected sky. Rotate the CPL and the glare slides off, revealing deep, rich tone in the stones, with reflections kept only where they help. There is no better filter for this city's wet streets.

Shop windows. The CPL lets you cut the reflection on glass and see through to the interior, or keep the reflection as a layered, double-exposure-like effect. You control which.

Water and foliage. It deepens the surface of the fountain in Piazza Maggiore and saturates the green of the Giardini Margherita.

Sky, for black and white. The CPL darkens a blue sky, which in monochrome means it controls how dramatic your sky tone is. A polarized sky goes deep grey, making clouds pop, exactly the drama high-contrast black and white loves.

The cost is 1 to 2 stops of light and the effect varies with angle, strongest at 90 degrees to the sun.

Glow Mist: atmosphere, in small doses

The Glow Mist filter blooms highlights into soft halos. Use it for:

Blue-hour neon, where streetlights and signs bloom into cinematic glow.

Atmospheric portraits, where you want a soft, dreamy, filmic quality.

And use it sparingly. A little is mood. Too much and every frame looks like it was shot through a greasy window. This is a filter to reach for two or three times a night, not to leave on.

ND: when light is the problem

Use ND when you have too much light for the creative setting you want: shooting wide open in bright sun, or a slow shutter for daylight motion blur. We covered this fully in the previous lesson. The point here is that ND solves an exposure problem, not a look; do not put it on unless light is actually in your way.

The stacking rules

Now the discipline. Each piece of glass costs light and adds flare risk, so:

Stack at most the CPL plus one ND. That covers nearly every creative need.

Never run all four at once. A tower of filters vignettes, flares, and softens the image.

Account for the light cost. The CPL eats 1 to 2 stops; the ND is calibrated to its rating. If you stack them, add the stops to know your real exposure room.

The best photographers carry filters they rarely use, because they have learned that a clean lens beats a clever one most of the time. Bring the kit. Use it when the situation truly calls for it. The rest of the time, protection glass or nothing, and let your eye do the work.