Baader 35nm H-alpha CCD Filter

Description

A wide bandpass H-alpha filter for astroimaging. Not suitable for Solar astronomy.

Mechanical Properties

• Parfocal and plane polished substrates. Each individual filter is optically fine-polished to 1/4 wave.
• Baader line filters are hard coated individually.
• Baader filters especially are not cut out of large size plate-glass, which is a typical manufacturing process for economy filters (cut-out filters exhibit micro-cracks around all edges. Capillary action between glass and coating layers will lead to premature ageing due to moisture deposition).
• All Baader filters have individual coating sealed edges, impermeable against ageing because the penetration of moisture is impossible.
• Baader filters are being tested repeatedly to comply with MIL-specifications. One common process is to boil the test specimen for one hour in salt water. Baader filters remained completely intact as opposed to filters drilled out of large glass plates.
• All Baader filters sport scratch resistant hard coatings which can be cleaned repeatedly throughout their entire lifetime as many times as needed – preferably with Baader Optical Wonder cleaning fluid.

Optical Properties

• Very low halo and reflective angle – compared to competing line filters.
• Balanced sensitivity and excellent coordination in the usual CCD characteristic allows the O III and S II lines recordings with virtually the same exposure time – very important for automated continuous shooting.
• Maximum colour contrast for each of four colour channels – achieved through steep slopes at all transmission curves combined with science approved placement of spectral windows.
• Dual cavity design – for applicability over a wide focal length range of f / 10 to f / 3 system.
• The O-III and H-beta emission lines are clearly separated – no colour distortion – results in the highest deep-sky quantum yield.
• Both photographically and visually the stars do not appear by any of the Baader line filters as multi-coloured “dunghill”, since each filter passes only the light to pass the respective emission line. In this context, a careful comparison of the various manufacturers published Transmission data sheets is recommended. In all Baader filter curves the entire spectral range is always shown with comparison to what a modern CCD chip can represent, typically (from 300 to at least 1200 nm). It can be seen, whether the offered filter has undesirable weaknesses in the spectral blocking. Many manufacturers only show the spectral region around the filter and are “silent” about their filter so-called “side lobes” (= holes in light suppression), which decreases the contrast and the cleanliness in the reproduction of the star colours sensitive.
• The 35nm H-alpha filter is tuned for interline CCD cameras the same exposure time brings as a 7 nm H-alpha filter on full-frame CCD cameras. So you can choose through the most balanced H-alpha filters for the various CCD cameras, 3.5Nm or 7 nm or 35 nm.
• H-Beta, O-III and both wider H-alpha filter (7 nm and 35 nm) are also outstandingly suitable as a visual contrast filter. On telescopes with larger opening than 250 mm gaseous areas occur very strongly marked in front of the star background. The stars appear drastically attenuated – as well as the urban sky pollution.

Specifications