ND Filters: Screw-On vs Built-In and How to Choose Strength

What an ND filter does

A neutral density filter reduces the light reaching the sensor without changing color. It does not alter focus, aperture, or the character of the lens; it simply cuts exposure. That lets you use a slower shutter speed or a wider aperture in bright conditions than the camera's meter would otherwise allow.

The strength of an ND filter is measured in stops of light reduction. A 3-stop filter cuts light by a factor of 8, letting you lengthen the shutter speed by 3 stops or open the aperture by 3 stops. A 6-stop filter cuts light by a factor of 64. A 10-stop filter reduces light by about 1000 times, which is useful for very long exposures of water, clouds, or crowds. The exact numbers depend on the filter's density rating, which is standardized across reputable manufacturers.

• ND2 reduces 1 stop (half the light)
• ND4 reduces 2 stops (quarter of the light)
• ND8 reduces 3 stops (one-eighth of the light)
• ND16 reduces 4 stops (one-sixteenth of the light)
• ND32 reduces 5 stops (one-thirty-second of the light)
• ND64 reduces 6 stops (one-sixty-fourth of the light)
• ND1000 reduces about 10 stops (roughly one-thousandth of the light)

Screw-on vs built-in ND filters

Screw-on ND filters thread into the front of the lens, like a protective filter but with optical density. They are sold in standard diameters that match the filter thread size printed on the lens barrel or in the manual. You can carry multiple strengths in a small pouch and swap them as conditions change. Screw-on filters work on almost any camera that accepts interchangeable lenses, from mirrorless cameras to DSLRs.

Built-in ND filters are optical elements that slide into the light path inside the camera body. They are found on some fixed-lens cameras, especially compact cameras and certain video-oriented models. The camera's menu or a physical switch activates the ND, often offering two or three strengths such as 2-stop, 4-stop, and 6-stop. Built-in ND filters are convenient because you cannot lose them, scratch them, or forget them at home. The trade-off is that you are limited to the strengths the camera offers, and you cannot combine a built-in ND with a polarizer.

How strength affects shutter speed and aperture

The whole point of an ND filter is to give you control over shutter speed and aperture in bright light. Suppose you are shooting a waterfall on a sunny day. At ISO 100, the meter might ask for 1/500 second at f/8. With a 3-stop ND filter, you could use 1/60 second at f/8, which blurs the water nicely. A 6-stop filter would take you to 1/8 second, producing a silkier effect. For a very long exposure of several seconds, you would need a 10-stop filter and a sturdy tripod.

For video, the constraint is often the shutter angle or the 180-degree rule. If you want a cinematic blur at 24 frames per second, you need a shutter speed near 1/50 second. In daylight, that usually requires an ND filter even at the base ISO and a closed-down aperture. A built-in ND makes this simple because you can dial in the exact strength from the menu. A screw-on filter also works, but you need to carry the right strength for the conditions.

Strength also affects aperture choice. If you want a shallow depth of field in bright sun, you need to open the aperture to its widest setting. At f/1.8 on a high-resolution camera, the shutter speed might exceed the camera's maximum, forcing you to stop down. An ND filter lets you keep the aperture wide open while maintaining a correct exposure.

Choosing strength for your use

For general outdoor photography, a 3-stop ND filter is the most versatile starting point. It lets you drop from 1/500 to 1/60 second for motion blur, or from f/8 to f/2.8 for subject isolation. Many photographers keep a 3-stop and a 6-stop in their bag. The 6-stop is useful for longer blurs of water, clouds, and crowds.

For video production, a variable ND or a set of fixed strengths such as 2-stop, 4-stop, and 6-stop covers most situations. If your camera has a built-in ND, learn its exact strengths and practice switching between them quickly, because the moment you need a different density is usually the moment you cannot swap a screw-on filter.

For long-exposure work, such as seascapes or architecture, a 10-stop ND filter is the standard choice. It turns a 1/30 second exposure into roughly 30 seconds, depending on the base exposure, which is enough to smooth water and remove people from a scene. Be aware that very dense ND filters can produce a color cast, which you can correct in post or by using a filter with high optical quality.

Practical considerations

Screw-on filters require the correct thread size for each lens. If you own lenses with different diameters, you need step-up rings or separate filters for each size. This is a common reason to standardize on one lens family: a Canon RF or Nikon Z system with a shared filter size simplifies the kit.

Built-in ND filters eliminate the risk of forgetting, losing, or breaking a filter. They also avoid the slight optical degradation that an extra piece of glass can introduce. However, they are not adjustable in infinitely small steps, and they cannot be combined with polarizers or graduated ND filters for creative effects.

If you shoot video with a 4K or 6K camera, a built-in ND is a major convenience because you can change density without removing the camera from a gimbal or rig. If you shoot stills and want maximum flexibility, screw-on filters give you more control over exact density and let you experiment with different strengths across different lenses.

• Carry at least two strengths: one mild (3-stop) and one strong (6-stop or 10-stop)
• On fixed-lens cameras, check if the built-in ND offers the strengths you need
• For video, verify that the built-in ND can be changed while recording or at least while the camera is on a stabilizer
• If you use screw-on filters, keep a step-up ring in the bag for lenses with different thread sizes
• Store filters in padded cases to prevent scratches and dust

What to pick for your use

Questions

Is a built-in ND filter as good as a screw-on one?

Yes, for most purposes. Built-in ND filters are made of the same optical glass and are positioned inside the lens, so they do not add any front weight and cannot be scratched or lost. The limitation is that you cannot choose arbitrary strengths, and you cannot combine them with a polarizer or a graduated ND.

What ND strength should I start with?

A 3-stop ND filter is the most useful for general photography because it gives a noticeable effect without making the viewfinder too dark. If you mostly shoot video, consider a 2-stop or 4-stop, depending on your camera's shutter-angle settings. A 6-stop is a good second purchase for stronger motion blur.

Can I stack two screw-on ND filters?

Yes, you can stack a 3-stop and a 6-stop to get 9 stops, which is useful for very long exposures. Stacking can introduce vignetting on wide-angle lenses and a slight color cast. Check the filter thread size in your manual to ensure the combined thickness does not block the lens.

Do built-in ND filters affect image quality?

No more than a screw-on filter. The optical element is part of the lens design and is optimized for the camera. Built-in ND filters do not add any extra reflections or flare, and they do not reduce sharpness.

Is a variable ND filter better than a fixed one?

Variable ND filters allow continuous adjustment, which is convenient for video when light changes. They are two polarizers that rotate, and they can produce an X-shaped darkening across the frame at very strong densities. Fixed ND filters are more consistent and have no such artifact. For critical stills, fixed filters are safer; for run-and-gun video, variable is practical.