How to choose a ND filter?

ND filters (Neutral Density filters) are probably one of the hardest accessories to choose for landscape and photography enthusiasts: square or circular? How many stops for daytime waterfall shots? Fixed ND or Variable ND — which is worth buying? This article helps you sort through all these choices at once.

I. What exactly does a ND filter do?

A ND filter is like putting "sunglasses" on your lens. It evenly reduces the light entering the lens without changing colors or requiring adjustments to shutter speed and aperture. Core uses:

• Long exposure: Creating a misty effect on flowing water or silky, streaked clouds during the day
• Large aperture needs: Shooting portraits/video at f/1.8 on sunny days — when the shutter speed can't go fast enough, use an ND filter to reduce exposure
• Video exposure control: Maintaining cinematic shutter speeds like 1/50s

Before buying, clarify your primary use - this directly determines all subsequent choices.

II. Square Filters vs. Circular Filters

Circular ND Filter (screws onto lens front)

Pros:

• Affordable, low entry cost
• Compact, easy to carry, screw on and go
• Good sealing, low risk of light leakage, no flare issues at seams
• Virtually no extra maintenance needed

Cons:

• Filter thread size issue: Different lenses have different diameters — either buy multiple filters or use step-up rings (which may cause vignetting)
• Hard to stack: Want to combine ND + graduated filter? Nearly impossible
• Thick filters on wide-angle lenses easily cause vignetting

Square ND Filter (slot-in, used with filter holder)

Pros:

• One filter holder works with all lenses — just swap adapter rings when changing lenses, saving money long-term
• Free combination: ND + Graduated ND (GND) + CPL in any arrangement
• Convenient composition: Move the GND transition line up and down to match the horizon
• Ultra-wide angles less prone to vignetting

Cons:

• High initial investment: Filter holder + adapter rings + filters
• Bulky, cumbersome to carry, time-consuming to set up
• Prone to dust, requires frequent cleaning
• Holder edges may leak light (especially with very dense ND filters)

How to choose?

In a word: Beginner + limited budget → circular; serious landscape → go straight to square system, don't take detours.

III. How many stops of ND should you buy? Match to your scenario

ND stops are categorized by light reduction levels: ND8 = 3 stops, ND64 = 6 stops, ND1000 = 10 stops.

1.Video shooting (1-5 stops)

To maintain 1/50s shutter speed in daylight, you typically only need 3-5 stops reduction (ND8~ND32). Too strong an ND forces higher ISO, degrading image quality.

2. Daytime waterfalls and streams (3-6 stops)

• For 0.5~2 second exposures with silky water effect: generally 6 stops (ND64) needed
• Weaker light (overcast, early morning/evening): 3 stops (ND8) is sufficient

This is the most commonly used stop, bar none — if buying your first ND, start with ND64.

3. Sea of clouds, streaking clouds, misty ocean (6-10 stops)

• For 15-second to several-minute exposures: typically 10 stops (ND1000)
• Best used around sunrise/sunset; nearly impossible at high noon

Note: Landscape photographers call 10+ stop NDs "black mirrors" — compose and focus before attaching.

4. Midday bright sun (15 stops/ND32000+)

To achieve silky water or completely empty streets at noon, you need 15+ stops or stack multiple NDs. When stacking, note: very high stops may require Bulb mode + shutter release cable.

Exposure conversion tip: For each ND stop, double the shutter time. E.g., without ND it's 1/125s; with 6-stop ND it becomes 1/125→1/2 second; with 10-stop it's 8 seconds.

IV. Fixed ND vs. Variable ND

Fixed ND

Pros:

• Stable image quality, no color cast (quality brands)
• No "X-pattern cross" issue found in variable NDs
• Relatively lower price, more options

Cons:

• Each stop requires a separate purchase, need to swap filters
• Traveling requires carrying multiple filters, cumbersome

Variable ND (VND)

Pros:

• One filter replaces many — adjustable from 2-9 stops with a twist
• Video shooting essential — adjust exposure on the fly without stopping to change filters
• Only one filter to carry, lightweight

Cons:

• Quality no-color-cast VNDs are expensive; cheap ones have noticeable color cast (often yellow/green)
• High reduction settings prone to "X-pattern" (dark cross), ruining the image
• Essentially a polarizer combination — improper rotation angle affects image quality
• Wide angle + high stop settings make X-pattern worse

How to choose?

V. Pitfall Avoidance Tips

• 1. Don't buy no-name cheap filters: ND filters seem simple, but poor quality products cause severe color cast and sharpness loss that can't be fixed in post. GiAi ND filters use multi-layer coating, low color cast, excellent quality — a solid choice.
• 2. Only buy Variable NDs from major brands: These are polarizing structure lenses requiring extremely high craftsmanship.
• 3. Check your lens thread size before buying: Look for the Ø value on the lens front (e.g., Ø77mm). If buying square, confirm adapter ring diameter too.
• 4. Long exposure trio: ND + tripod + shutter release cable (or 2-second self-timer). Missing any one could ruin the shot.
• 5. Compose before mounting black mirrors: 10+ stop NDs make the viewfinder go completely black — frame, manual focus, and set parameters before attaching.

Summary

• Shape: Beginner/single lens → circular; multi-lens landscape → square system
• Stops: Video 3-5 stops, water flow 6 stops (ND64), streaking clouds 10 stops (ND1000), midday 15+ stops
• Fixed vs. Variable: Photos → fixed (ND64+ND1000 is the golden combo); video → variable from a reputable brand

Clarify what you shoot most often, and the answer will become clear. Happy shooting stunning long exposures!