From Phones to Drones: What Exactly Is a Camera Module and Which Filters Live Inside?

A camera module isn't just a simple box—it is a precision-engineered stack that combines a lens assembly, image sensor, mechanics and actuators, optional onboard electronics, and carefully placed optical filters or protective windows. Why do filters matter? They select which wavelengths reach the sensor, suppress unwanted stray light and reflections, protect against IR or UV contamination, and can even boost signal-to-noise for specific spectral bands. Filters can be found on the sensor cover glass, packed as flat plates just behind the lens or window, as coatings on optical surfaces, or as dichroic beamsplitters in multi-sensor designs. Phones focus on color fidelity and compactness; security cameras add day/night IR-cut switching; drones include swappable ND, polarizers, or narrow bandpass filters for demanding applications.

A camera module is a small, integrated unit designed to capture images or video. The building blocks are largely consistent across devices, from smartphones to drones and industrial robots:

• Lens assembly: Several optical elements, sometimes with autofocus (AF) and optical image stabilization (OIS) mechanisms.
• Image sensor: Usually CMOS for speed and power efficiency—specs dictate resolution, frame rate, dynamic range, and sensitivity.
• Mechanical housing: Precision holders, spacers, or wedges to guarantee optical alignment and set parameters like focal distance and tilt.
• Electronics: Flex cables, built-in processors, or heaters for rugged or outdoor modules.
• Optical filters / windows: Crucial for controlling and protecting the light that hits the sensor.

A lens module contains just the optics and mechanics. A camera module includes the sensor and possibly the electronics. All filter concepts here apply to both, but especially to modules with integrated sensors.

Filters are distributed according to their function and system design:

• External window or dome: The first line of defense, often coated with AR, hydrophobic, or hard coatings. Specialty filters here include laser-safety notches or broad UV/IR block for rugged devices.
• Lens surfaces: Usually broadband anti-reflection (AR), sometimes with color-balancing tints to manage flare and color cast.
• Flat filter plates: The classic spot for thin IR-cut, UV/IR-cut, ND (neutral density), polarizer, or custom bandpass filters—may sit deep in the barrel or just behind the front window.
• Beamsplitters or dichroics: Found in multi-sensor systems, these split or combine spectral channels (visible, NIR, SWIR, laser).
• Sensor cover glass: Often integrates the IR-cut or a wavelength-specific bandpass, saving space and reducing alignment headaches.

Note for wide FOV/ultrawide modules: Interference filters will shift in wavelength (blue-shift) at oblique angles (AOI shift), so system design must accommodate this effect.

Core filter types: IR-cut is key for blocking near-IR to ensure color accuracy; ND cuts down overwhelming light in bright scenes (especially for drones); polarizer is critical for glare control on difficult surfaces; bandpass is used for multi-spectral or mapping systems; AR coatings suppress flare; beamsplitters/dichroics split or route spectral channels for different sensors; and special add-ons like EMI meshes or heaters enable specialized rugged missions.

Phones: Thin, integrated IR-cut (on sensor cover); ND or polarizer is usually an external clip-on accessory.
Security cameras: Motorized IR-cut for day/night transitions, AR coated and ruggedized windows, sometimes anti-fog heaters.
Drones / Gimbals: Rugged, swappable front filters (ND, polarizer), options for specialized bandpass for mapping or inspection or lidar tasks.

No matter the system—drone, phone, or CCTV—filters are the unsung heroes that tailor your image, block noise, and protect the sensor. Understanding where the filters live and what they do allows you to pick or specify the right module for your application, so what you see is truly what you get.