Baader Planetarium Photometric Filters
Baader Planetarium 1.25" Photometric Filter Set
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.
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. Baader Filters will truly last lifetimes.
The 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 (1¼" Filter clear aperture is 27mm). The special threading has been designed to fit the wide variety of eyepieces and accessories (there is significant variation between the 1¼" filter threading used by eyepiece and accessory manufacturers). The front 'crown' of the filter cell incorporates milled notches which make handling and threading the filter a more secure operation in the dark.
Despite the 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.