The Narrowband StarGuy H Alpha, FWHM 7nm, filter is a deep red long pass filter that enhances the contrast of nebulae emissions and reduces the effects of light pollution by only passing the hydrogen alpha light. The H Alpha filter is designed to transmit a narrow band of Hydrogen increasing contrast, which is ideal for emission nebulea, like the Horsehead and North American. The filter eliminates halo effects with double sided polishing technique and coatings.