Optical thin films are widely used in optical instruments and measurement and control technology, thereby affecting various aspects of our life and making it diverse and colorful. Unlike conventional applications of optical thin films, this review focuses on the combination of optical thin films with optical microscopy imaging techniques. The main research plan is to develop planar thin film photonic devices for unmarked microscopic detection based on noble metal thin films loaded with surface plasmon waves and dielectric multilayer thin films with photonic bandgap structures. Owing to its planar structure and mature manufacturing process, this type of photonic thin film element can be made compatible with conventional bright field and wide field microscopic imaging systems, which makes it an ideal substrate for a test sample or can be used as a plugin for the imaging system. Such devices can utilize the near-far field interaction characteristics of thin films and light waves to regulate the illumination field of the system for achieving dark field illumination, total internal reflection illumination, and edge enhanced illumination. The contrast and detection sensitivity of imaging can be improved by changing the lighting method, leading to the development of multimodal, unmarked optical microscopy imaging and sensing systems with high sensitivity and contrast. To utilize the characteristics of simple structure, wide field, high sensitivity, and unlabeled imaging of this system, it has been applied to the field of environmental photonics for in situ, real-time, and nondestructive investigation of the hygroscopic growth process of a single ultrafine particle in a real atmospheric environment. Thus, this imaging system is expected to provide strong scientific support and technical tools for tracing of and further research on atmospheric haze.