Filtro UBVRI Bessel I 31mm

Bandpass filter suitable from f/15 to f/1.8

• Classic photometric filter with Bessel passband - 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 as well as for older CCD camera technologies

Filters for scientific photometry: The UBVRI system was developed in the 1950s for the McDonald Observatory 0.9 m telescope and consisted first of a Johnson UBV filter set, later becoming cousins with the R and I filters in the red Expanded range of spectrum. The Johnson and Cousins extended UBVRI system filters include:

• U - Ultraviolet, with a transmission window between about 320 and 400 nm
• B - Blue, with a transmission window between about 400 and 500 nm
• V - Visible, i.e. visible light, with a transmission window between about 500 and 700 nm
• R - Red, with a transmission window between about 550 and 800 nm
• I - Infrared, with a transmission window between about 700 nm and 900 nm.

Bessel filters for the digital age: In 1990, MS Bessel dealt with the subject in order to find a filter combination for the CCD cameras, which were becoming increasingly common at the time. These Bessel UBVRI filters are still standard today and are also the most widely used in amateur circles such as the AAVSO. In particular, the V filter has proven itself as an inexpensive entry into photometry: it roughly corresponds to the visual brightness; since only one measured value is used, this is ideal for getting to know the techniques.

The filters of this series are characterized by:

• Reflex-Blocker™ coatings for the greatest possible insensitivity to retro-reflection from the nearest auxiliary optics, even under the most adverse conditions
• Identical filter thickness to existing standards, with great care for homofocality
• Blackened edges all around, with filter front indicator in the form of a black outer edge on the telescope side, in order to additionally avoid any reflection from light falling on the filter edge
• Each filter is individually fine-optically polished and coated, with a sealed coating edge (NOT cut out of a larger plate - with the coating edges exposed as a result, see more about this here)
• Life-Coat™: even harder coatings to enable an aging-resistant coating over an unlimited service life - even in the most adverse environments