AstroStreet UHC filter for 1.25 inch (31.7mm) filter diameter

UHC---ultra high contrast
As the name suggests, it enhances the darkness of the background of the sky and enhances the contrast of gas nebulae.

It is a filter that transmits only wavelengths in a specific band, and is called a nebula (nebula filter).

Among Nebular filters, this filter has a wide transmission bandwidth and is designed to transmit Hβ rays (Hydrogen-Beta) and OIII rays (Doubly ionized oxygen).
Dramatic effects over a wide range such as observation of diffuse nebulae (Great Orion Nebula, etc.), planetary nebulae (Ring Nebula, etc.), and faint diffuse nebulae. Effective for observations on the ground

[Sleeve diameter] 1.25 inch (31.7mm) filter diameter