The UHC-S Nebula Filter - 1.25-Inch Round Mounted by Baader Planetarium:
This Baader Planetarium UHC-S Nebula filterexcels at delivering a high-contrast and natural view of emission nebula without excessive dimming and loss of background star fields. The perfect filter for viewing emission nebula from light polluted skies, or for boosting the contrast of nebula from dark sky sites. The advanced technology coatings enable the filter to achieve an outstanding transmission of over 97-percent across the entire pass band, with total blockage of prominent light pollution lines. This translates to maximum image brightness and contrast. Owners of 4 to 10-inch telescopes will especially appreciate the high efficiency, and larger scope users will love the rich star fields and detailed subtle nebular shadings that are left intact.
The Baader UHC-S manages to improve on the contrast of the typical broadband or so-called "Deep Sky" filters. Sky background is darker, and contrast of emission nebulae are noticeably improved. Most other "UHC" filters tend to excessively darken the sky and star fields, leaving the nebulae looking artificial and flat, set against an empty background. The high transmission, sharp cutoffs, and more moderate 60 nm pass band of the Baader UHC-S filter retains a more natural view, yet significantly boosts overall contrast. Imagers will appreciate the broader pass band and inclusion of an extremely efficient H-alpha pass band (>99-percent at 656 nm), as well as the extreme optical quality.
At the heart of the Baader UHC-S filters are their special fine optical substrate polishing process and advanced coating design. The result is a filter that imparts no image degradation, unlike other filters. To prevent deterioration from cleaning or exposure to moisture, some other filters even resort to sandwiching their delicate coatings between two layers of filter glass, resulting in potential blurred or double images. The combination of hardened coatings and fine optical substrate of the Baader UHC-S avoids this image degradation. A common misperception is that deep sky viewing is limited to low powers, and image resolution is not as important as in planetary observation. In reality, high magnifications are very common and useful in studying fine details, particularly for the brighter diffuse and planetary nebulae. Baader UHC-S filters can take high magnifications, and stars retain their pinpoint sharpness, even if the filter is used far ahead of the image plane (i.e. for imaging use, or ahead of a star diagonal or binoviewer). Baader filters fulfill the requirements of an ideal filter, to perform their filtration at highest efficiency without any other detectable effect on the image.
Baader Planetarium UHC-S Nebula Filter Features:
True Optical Quality: Baader glass substrates are of true optical quality. Most other filters are merely made from raw flame-polished, optically flat, or sometimes a top quality commercially polished filter glass (fine for camera filters), resulting in wavefront deformations that damage image sharpness and contrast when used with telescopes. Baader Planetarium filters are made from striae-free substrates, and actually fine optically polished flat to within 1/4 wave p-v over the entire surface, plane parallel to within 30 seconds of arc! This important and unique custom step adds cost - but the result is a filter that maintains the full wavefront quality of the telescope without double images or ghosting, even at high magnifications. Critical to maintaining this level of flatness are Baader's carefully balanced coating designs, which prevent coating surface stresses from warping the substrate. Such high flatness enables Baader filters to be used far in front of the focal plane, ahead of star diagonals and digital cameras. They are particularly well suited for attachment to the nosepiece of the Maxbright Binocular Viewer (other manufacturer's filters must be used in pairs, attached to the eyepieces).
Filter Durability:Filter durability has always been a hallmark of Baader Planetarium. The multi-layer dielectric coatings are plasma-assisted and Ion beam-hardened using the latest technology (the coatings are harder than the glass substrate itself!). Baader filters withstand repeated real-world exposure to the elements and physical cleaning. Users need not leave their precious filters dull and dust encrusted to avoid cleaning - Baader filters may be used and cleaned without fear. We have heard sad stories from owners of other simpler soft-coated dielectric filters, who have seen their coatings degrade from normal exposure to moisture, or wiped away from routine cleaning. Some manufacturers even resort to sandwiching their delicate coatings in between two layers of glass (and risking blurred double images as well as eventual degradation from the edges inward). Baader Filters will truly last a lifetime.
Stackability:Unlike other filters, Baader Planetarium filters are truly designed to be stacked and combined. This is possible due to the high optical quality and highly efficient anti-reflection multi-coatings. The ability to combine filters opens up many exciting possibilities, permitting unique spectral characteristics unachievable with any single filter.
Special Filter Cell:Baader's special filter cell design offers unique features that enhance their reliability and usability. Though difficult to produce, the ultra-thin filter cell results in the maximum possible clear aperture, in order to minimize vignetting (the 1.25-inch Filter clear aperture is 27 mm, the 2-inch Filter aperture is 45 mm). The special threading has been designed to fit a wide variety of eyepieces and accessories (there is significant variation between the 1.25-inch filter threading used by eyepiece and accessory manufacturers). The front crown of the filter incorporates milled notches which make handling and threading the filter a more secure operation in the dark.
Low cost:Despite high quality and advanced technology, Baader Planetarium filters are affordable. By leveraging high volumes across all filters in the Baader family, these filters can be offered at very reasonable prices.