The Optolong L-Enhance is a dual-band filter that has been designed for use with digital SLRs (DSLR), color CMOS cameras and monochrome CCD cameras. The filter combines simplicity of use with a moderate price, making it a strong alternative to a set of narrowband filters.
The filter allows light to pass through the main H-alpha hydrogen line (656 nm) and O-III double ionized oxygen (500 nm), and helps to eliminate the influence of moonlight and artificial city lights such as street lighting. It improves the contrast and visibility of numerous Deep Sky objects, especially emission nebulae.
More information about Optolong filters and the manufacturer on the product page (active link 06.2020): https://www.optolong.com/cms/document/detail/id/14.html