Unlike many white-light solar filters that produce views of the sun with a red-orange, bluish, or yellow tint, the Alpine Astronomical 120mm Baader AstroSolar BDSF 3.8 White-Light Digital Solar Filter reveals the sun in its natural white color. With an optical density of 3.8, this iteration is specifically designed for digital imaging of the sun and all phases of a solar eclipse through an optic like a telescope or extreme telephoto lenses — showing more surface details with greater clarity versus other types of solar filters. The filter is mounted onto a clear-white IR-rejecting plastic ring, which acts as stabilizing element for the filter cell, and the ring is in turn mounted onto the aluminum front frame. The thermal expansion coefficient of the plastic and the film are similar to minimize thermal stress on the film for increased resistance to developing pinholes or tears.
With the ability to be installed on the outside or inside of an optical tube assembly, dew shield, or corrector plate retaining ring, this filter provides a safe way to view the sun through conventional nighttime telescopes. Recommended for apertures from 110-130mm, the filter is engineered with three centering bolts that can fit OTAs, dew shields or corrector plates with an outside diameter of 140-180mm, or an inside diameter of 170-210mm. Due to the shallow depth of the corrector plate on most catadioptric OTAs, for secure and safe use Alpine Astronomical only recommends outside mounting on Cassegrain-style telescopes.
This filter is only intended for digital imaging of the sun, and is not safe for direct solar viewing or for use on cameras with an optical viewfinder. Only use on cameras with an electronic viewfinder (EVF) or Live-View option. If you do not know what kind of viewfinder your camera has, do not use this filter.
- For the correct fit, measure the outside or inside diameter of the dew shield/lens housing - including hardware like retaining rings and screw heads — and choose the size that matches the measurement with some extra room
- When used on Schmidt-Cassegrain, Maksutov-Cassegrain, or other catadioptric OTAs, outside mounting is required as the limited depth of the front inside diameter prevents full and secure engagement of the centering bolts
- Recommended for 110-130mm apertures
- 170-210mm inside diameters
- 140-180mm outside diameter