Meade Series 4000 Nebular Filters incorporate the very latest in interference coatings technology. Each filter includes more than 40 coating layers to precisely reject unwanted light from urban light pollution while allowing critical nebular emissions to pass with minimal reduction. The Meade Broadband Nebular Filter strongly rejects the light of sodium- and mercury-vapor lights as well as natural airglow and auroral emissions. The Meade Broadband Filter also passes photographically-important Hydrogen Alpha nebular light, making the filter a valuable aid in the photography of deep-space emission nebulae. The contrast between galaxies and the night-sky backdrop is enhanced by the filter, but because galaxies emit light in a much broader range of wavelengths than nebulae the effect is generally not as dramatic in these cases. This filter's clear aperture is 26mm.