Pinholes

Pinhole refers to a very small opening or perforation that can occur in various contexts, from imaging devices to coatings and membranes. Pinholes can be intentional design features or accidental defects, and their presence can indicate a specific function or a failure mode depending on the application. They typically range from micrometers to fractions of a millimeter in diameter.

In photography and imaging, a pinhole is a tiny aperture used in pinhole cameras. These cameras have no lens; light passes through a single small hole to form an image on a light-sensitive surface inside a light-tight body. The result is a very deep depth of field and a soft, diffuse appearance. Pinhole sizes and exposure times determine sharpness and contrast, with common pinhole diameters in the sub-millimeter to sub-millimeter range.

In coatings, films, membranes, and similar materials, pinholes are defects that allow unwanted passage of liquids, gases, or light. They can arise from substrate imperfections, contamination, drying stresses, or improper curing. Pinholes can compromise barrier properties, corrosion resistance, or electrical insulation, and are often detected by visual inspection, dye penetrant testing, air-leak tests, or electrical methods.

Prevention and remediation depend on the context. In coatings, measures include improving surface preparation, selecting compatible primers, controlling curing, and applying appropriate thickness with proper sealant touch-ups. In membranes or films, process adjustments aim to reduce porosity and seal defects during fabrication.

The term pinholes may also appear in medical or dental discussions to describe tiny openings, though such uses vary by field and are described within those disciplines.