One of our High Transmission (HT) precision range of filters, this 2" H-Beta Filter is sure to impress on performance, quality and price. It comes with its own individual data sheet of performance - guaranteed! It is an extremely useful filter for observing the very feint nebulae. It has a very limited transmission range of 484 - 490nm (70%) and 478 - 483 & 492- 497nm (60+%). The very sharp cut offs only allow the hydrogen beta light that these feint objects emit to pass through. By cutting off almost all of the visual spectrum the filter effectively blackens the sky to make these objects show through. This filter is best used on large aperture telescopes (8" +) under very good seeing conditions and is an essential item for those astronomers who enjoy tracking down the most elusive of deep space objects. This is a filter for visual observational use.