Commercial narrowband Fabry-Perot solar filters, methods and instruments for their examination

Nowadays, Coronado, Lunt, Solar Spectrum, Daystar and Solarscope companies advance available narrowband solar filters. Being installed in small telescopes they allow amateurs not only to admire grand phenomena in the solar atmosphere but also to be involved in scientific observations. The efforts of the companies aimed at achieving extreme values of Fabry-Perot (FP) filter basic parameters such as full width at half-maximum, angular field of view, filter clear aperture and uniformity of passband over the aperture, to make them suitable for scientific observations. Parameters of commercial filters, their compliance with the requirements depend on filter design and technology developed by companies. This study considers narrow-band FP filters designs proposed by five leading companies, and some technological problems of their production, which are important for their operation. To use commercial filters in professional research, it is necessary to be sure that the filter parameters declared by companies correspond to real ones. The methods and devices proposed by authors allow high-precision measuring integral and local characteristics of FP filter and its spectral uniformity across the aperture. Also, we can estimate the quality of optical stack and filter suitability for professional solar observations.