K&F 37mm 4-in-1 Filter Kit — Nano-K UV, CPL, ND4, Protective (37 mm)

The K&F 37mm 4-in-1 Filter Kit includes a Nano-K UV, a circular polarizer (CPL), an ND4 neutral density filter and a protective filter, all sized for lenses with a 37 mm thread. This compact set is designed to provide basic optical protection, reduce ultraviolet haze, control reflections on non-metallic surfaces and decrease light transmission when longer exposures or wider apertures are required. The filters are lightweight and suitable for small prime lenses, compact zooms and many mirrorless or DSLR setups that accept 37 mm screw-in filters.

Advantages

The Nano-K UV filter blocks ultraviolet light and helps maintain color fidelity while offering surface protection for the front element. The circular polarizer reduces glare and improves contrast in skies, water and reflective surfaces without affecting autofocus performance. The ND4 neutral density filter reduces incoming light by two stops to enable slower shutter speeds or wider apertures under brighter conditions. The protective filter serves as a physical barrier against dust, moisture and minor contact damage. The set’s uniform 37 mm size simplifies swapping filters and keeps weight and bulk to a minimum.

Suitable for

• Everyday lens protection for compact lenses and adapters with 37 mm threads
• Landscape photography to deepen skies and cut reflections using the CPL
• Portraits and low-light shooting when ND4 allows wider apertures or controlled depth of field
• Travel and street photography where compact, lightweight accessories are required

Key specifications

• Filter thread size: 37 mm
• Filter types included: Nano-K UV, circular polarizer (CPL), ND4 neutral density, protective clear filter
• ND strength: 2 stops (ND4)
• Construction: multi-coated glass elements with metal or alloy slim ring (design varies by model)
• Compatibility: lenses with 37 mm screw-in filter mount

How to use

Screw the appropriate filter onto the front of a compatible 37 mm lens until it sits snugly; avoid overtightening. Use the UV filter or protective clear filter as a permanent guard against dust and scratches. Rotate the circular polarizer while observing the effect through the viewfinder or on the camera screen to achieve the desired reduction in reflections and increased color saturation. Attach the ND4 when you need to reduce light by two stops to lengthen exposure times or allow a wider aperture in bright conditions. Remove or change filters as shooting situations require, and store them in their protective case to prevent scratches when not in use.

Usage recommendations

Keep filter threads and lens threads clean and free of grit before mounting to avoid cross-threading. When using the CPL, compose and check polarization effect at the shooting distance and angle to the light source; the strongest effect is typically at 90 degrees to the sun. For long exposures with ND4, use a stable tripod and mirror lock-up or electronic shutter if available to minimize camera shake. Clean filters with a soft microfiber cloth and appropriate lens solution; avoid abrasive materials.