1¼" H-Beta narrowband filter (5.5nm) – Optimized CMOS

Baader H-Beta Filter: the H-Alpha filter for the eyes!

Baader's H-Beta filter with a half maximum width (HBW) of 5.5nm is particularly effective for telescopes with a mirror diameter of more than 8 inches, or if you are working with large exit pupils. This narrowband nebula filter shows significantly higher contrast compared to usual visual H-Beta filters with a larger spectral bandwidth. H-Beta nebula filters with a wide HBW provide a brighter image field and also show the California Nebula, for example, but less clearly and with much less internal structure. Without any filters, this California nebula (to cite just one example) is no longer recognizable even with a slightly lit sky.

About Baader H-alpha filters and why they are suitable for visual reasons

The development of narrow band H-alpha filters quickly proved to be a "game changer" for amateur astrophotography. In no other spectral line of emission nebulae in the sky can so much basic information for creating "pretty pictures" be gathered as in this hydrogen line. Mainly because today, due to advances in coating technology, CCD cameras, motorized focusers, and last but not least, the incredible tracking accuracy of modern amateur mounts, you can expose for longer and longer with increasingly narrow band filters. With astrophotography today, exposure times of 30 hours are not uncommon thanks to the three well-known extremely narrow band nebula filters. The mount just has to be able to track "sub-pixel accuracy" for hours; the focuser must not rotate even a micron (despite the heaviest cameras...) and the motorized focuser must be able to compensate for loss of image sharpness caused by temperature changes with an accuracy of thousandths of a millimeter. .. All this is possible - with excellent equipment.

Visually, this enormous instrumental effort would be unnecessary. Unfortunately, H-alpha filters, which are so beneficial in photography, are almost ineffective for DeepSky's visual applications, because the human eye is very insensitive in this wavelength range due to the color shift between day and night. night at low brightness levels. The day-adapted eye can recognize H-alpha very well, which works well, for example, in solar chromospheric observation in the light of the H-alpha hydrogen line. However, with DeepSky's visual observation in H-alpha and an eye that is forced to adapt to weak light, one only looks into a "black hole". The eye is not supposed to integrate light.

Most visual observers resort to the well-known O III filter, the human eye has its highest sensitivity in this wavelength range around 500nm to 520nm and this wavelength reveals numerous structures in SN remnants, planetary nebulae, etc. However, this is of little help for objects that shine predominantly in H-alpha.

The alternative: Baader H-Beta filters for visual use

For the H-alpha objects mentioned above, the H-beta line opens up an interesting possibility, because at 486 nm it is still very close to the eye's maximum sensitivity and due to quantum mechanical coupling to H-alpha, the same structures often appear. . . Also, since the vast majority of nebulae emit in the light of hydrogen, the much less popular H-Beta filter is much more effective than OIII.

Therefore, an H-beta filter can be seen as a visual H-alpha filter.

The H-Beta spectral range is really very interesting. Although quantum mechanics assumes a fixed ratio of H-alpha to H-beta hydrogen emission, H-beta is more energetic due to its shorter wavelength. As a result, the H-Beta emission is further attenuated as it passes through dusty regions. This results in noticeably higher H-Beta extinction than with H-Alpha light. The ratio of this change allows conclusions to be drawn about the density of the passing dust, which is particularly interesting for science. For astrophotography, H-alpha light can be reduced to mimic the effect of an H-beta filter, and vice versa, H-alpha structures appear visually and are virtually inaccessible to the eye in the original light.

For visual observers, the fact is that an H-Beta filter on hydrogen emitting nebulae can show very impressive effects in visualizing dust fractions in the nebula, similar to a photographic H-Alpha filter. As described at the beginning, the California Nebula is clearly outlined and has clear internal structures. Even the division into two strips can be seen very well with a larger telescope aperture, also the smooth fading towards the ends.

The filter effect described above is equally impressive in cometary dust tails. It is precisely this shorter-wavelength light that is scattered more strongly in the dust tail, increasing its contrast with the surroundings. Of course, even shorter wavelength light can further intensify the effect, but then we leave the eye's maximum sensitivity again. Therefore, the true extent of the sometimes extremely long dust tail can only be seen visually with the help of an H-Beta filter. Furthermore, since H-beta lies outside the dominant bands of the gas/ion tail, this offers the possibility of distinguishing the dust tail from the gas tail and also further increases the background contrast of the dust tail. dust.

Conclusion:

Visually, a dielectric H-Beta filter is not a universally applicable filter, like a neodymium skyglow filter. But it is by far the best tool for recognizing particularly delicate details, since, unlike the OIII filter, it makes the dominant hydrogen emission in the sky visible to the eye. Together with an OIII filter it covers the most important range of mist emissions and should not be missing from any "filter toolbox".

The new generation of Baader filters optimized for CMOS is characterized by:

Baader filters optimized for CMOS

higher contrast

full widths even narrower at half maximum (FWHM)

Reflex-Blocker™ coatings for the highest possible insensitivity to retroreflection from the nearest auxiliary optics, even in the harshest conditions

Carefully designed FWHM for each filter category to allow 1:1:1 exposures tuned to typical CMOS quantum efficiency and signal-to-noise ratio

Filter thickness identical to existing standards, with the greatest care regarding homofocality

Blackened edges all around, with front filter indicator in the form of a black outer edge at the front to further prevent any reflection of light falling on the edge of the filter.

Each filter is individually polished and optically fine coated, with a sealed coating edge (NOT cut from a larger plate, with the result that the coating edges are exposed, see more on this here)

Life-Coat™ – even harder coatings to allow an aging resistant coating for unlimited life, even in the harshest environments

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