Baader Planetarium Dark Blue 435nm Bandpass Filter 1.25" Eyepieces

Priced: $38.00
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Baader Planetarium Dark Blue 435nm Bandpass Filter 1.25" Eyepieces -

The Baader Planetarium Dark Blue 435 nm bandpass filter has a bandpass at 435 nm and is designed for 1.25" eyepieces. A fine optical polish and 2 mm thick glass allows this filter to be inserted anywhere into the optical path without introducing astigmatism or other defects. For instance, it can be used in front of a binocular viewer without degrading the image in any way. Substrates are free of striae and plane-parallel polished to within 30 seconds of arc. This eliminates any double images or ghosting due to wedge errors in the glass.
The filter cell features the largest clear aperture of any telescope filter on the market for complete freedom from vignetting at any focal length. The front "crown" incorporates milled notches, which makes handling and threading the filter an easy operation in the dark. All surfaces are treated with a 7-layer Multi-Coating, featuring a mere 0.25% residual reflection. It is the most elaborate coating ever applied onto amateur color filters, resulting in a filter free of any false reflections under any incident angle of light.
Light is the hottest commodity for all planetary observation. Especially during high magnification work, whether you have enough light or not is the deciding factor for the recognition of the subtlest planetary surface detail, much more important than a horde of different filters of mediocre execution. The 7-layer MC-coatings not only provides a brighter image, they prevent the softening effect of scattered light. Scattered light kills exactly those subtle features in planetary detail that you are longing to see. Painstaking attention to coatings and perfect optical figuring are simple reasons why the image contrast through these premium filters is so rock-solid.

Lining and Layers:

  • Finest 7-layer hard multi-coatings on both faces feature 0.25% residual reflections (Baader filters are unique, no other colored filter incorporates anti-reflection multi-coatings)


  • With the 2" size, only one filter is needed for binoviewing. Only Baader colored filters have the optical quality necessary for use this far ahead of the focal plane


  • Extremely high transmission results in maximum contrast and isolation of planetary details, even with smaller telescopes
  • Striae-free substrates are polished parallel to within 30 seconds of arc to avoid wedge errors
  • Carefully designed spectral characteristics. Filters may be stacked without image degradation or ghosting in order to provide even narrower passbands, or combine with any of the other Baader filters for interesting possibilities
  • No reduction in sharpness, even at high magnifications or when using the filter far ahead of the focal plane (i.e., digital imaging, or in front of a diagonal or binoviewer)
  • Efficiency of the bandpass filter (Dark Blue) achieves 70%
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Eyepieces:1.25" / 3.17cm
Glass thickness:2 mm / 0.07"
Transmission efficiency:70%

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