Bandpass filter, suitable from f/15 to f/1.8
- Classic photometric filter with transmission range according to Bessel – parfocal with all Baader filters of the same size
- Manufactured with state-of-the-art ion beam coating technology / daylight proof
- Equally suitable for modern CMOS cameras and older CCD camera technologies
Filters for scientific photometry: The UBVRI system was developed in the 1950s for the 0.9 m telescope at McDonald Observatory and initially consisted of a set of UBV filters according to Johnson. It was later expanded by Cousins to include R and I filters in the red region of the spectrum. The filters of the extended UBVRI system according to Johnson and Cousins include:
- U – ultraviolet, with a transmission window between approximately 320 and 400 nm
- B – Blue, with a transmission window between approximately 400 and 500 nm
- V – Visible, i.e. visible light, with a transmission window between approximately 500 and 700 nm
- R – Red, with a transmission window between approximately 550 and 800 nm
- I – Infrared, with a transmission window between approximately 700 nm and 900 nm.
Bessel filters for the digital age: In 1990, M. S. Bessel set himself the task of finding a filter combination for the CCD cameras that were becoming increasingly popular at the time. These Bessel UBVRI filters are still the standard today and are also the most widely used in amateur circles such as the AAVSO. The V filter in particular has proven itself as an inexpensive introduction to photometry: it corresponds approximately to visual brightness; since only one measured value is used, it is ideal for learning the techniques.
The filters in this series are characterised by:
- Reflex-Blocker™ coatings for maximum insensitivity to retro-reflection from nearby auxiliary optics, even under the most adverse conditions
- Identical filter thickness to existing standards, with the utmost care taken to ensure homofocality
- Blackened edges all around, with filter front indicator in the form of a black outer edge on the telescope side to additionally prevent any reflection from light falling on the filter edge
- Each filter individually precision-polished and coated, with sealed coating edge (NOT cut from a larger plate – with exposed coating edges, see here for more information)
- Life-Coat™: even harder coatings to enable an age-resistant coating with an unlimited service life – even in the most adverse environments
