The thin sheet of metal (or lens frame) in an optical system that confines the light beam through the inner hole of the metal frame of an optical part is called a diaphragm, which is an optical element. The shape of the diaphragm depends on the application. Most diaphragm sheets are circular, with the center distance of the diaphragm coinciding with the optical axis of the system and the plane of the diaphragm perpendicular to the optical axis, and are commonly used in cameras or HD camcorders.

The role of the diaphragm is divided into the following categories：

1．Aperture diaphragm is the effective diaphragm, its role through the plane of the optical axis to determine the aperture angle of the plane beam emitted from the axis point. Such as magnifying glass, telescope on the use of.

2．Field of view diaphragm is a kind of diaphragm used in the object plane or image plane to limit the imaging range, photographic system, camera system specially placed in the card door.

3．A vignetting diaphragm is a lens frame, often used on photographic objectives, that allows a certain amount of vignetting to exist so that off-axis points are imaged with a beam narrower than the on-axis points.

4．Eliminate stray light diaphragm, non-imaging objects emitted by the light into the system, reflected by the inner wall of the instrument to form a projection knife imaging surface, part of which is reflected by the refractive surface, after multiple reflections projected onto the image surface, known as stray light or stray light.

The diaphragm sheet adopts 304 stainless steel material after chemical etching processing, the thickness of the diaphragm sheet used 0.05mm/0.1mm/0.12mm/0.15mm/0.2mm and other thickness of stainless steel material. The appendix sheet etching processing method: the hole should be vertical, the hole wall is smooth, the true roundness of the hole is high, the hole diameter tolerance is strict, and the overall flatness of the product is high.