Manufacturer: Baader
Product number: BA2961751B

EUR 150,00


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Baader UBVRI Bessel B Filter 31 mm - photometric
The UBVRI system used today for scientific photometry was developed in the 1950s for the 0.9 m McDonald Observatory telescope and initially consisted of a Johnson UBV filter set, later extended by Cousins to include the R and I filters for 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 about 320 and 400 nm
B – Blue, with a transmission window between about 400 and 500 nm
V – Visible, 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.


According to the state of the art at that time, the filters had different thicknesses and transmittance values as well as no sharply defined edges (if any). Their spectrum therefore corresponds to a curve instead of a plateau.

In 1990, M. S. Bessel looked into the subject in order to find a filter combination for the new CCD cameras that were becoming increasingly widespread 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. The V-filter in particular has proved to be an inexpensive introduction to photometry: It corresponds approximately to the visual brightness; since only one measured value is used, this is optimal for getting to know the techniques.

Since 2010, Baader Planetarium has offered photometric UBVRI filters according to Bessel, which protected the coloured glasses from ageing with a dielectric coating and at the same time provided the desired transmission properties. This is not at all a matter of course: unfortunately, comparisons by the AAVSO have shown that not every modern "Bessel filter" actually shows the irregular flanks of genuine Bessel filters, but instead there are often plateaus with steep flanks. These steep slopes are easily achievable with dielectric filters, but the data obtained with them are simply not comparable, or only with difficulty, with the old data sets. Compare for yourself: You can find the transmission spectra in the product description.

New generation of Baader Planetarium UBVRI filters

Baader could not further improve the characteristics of their previous Bessel-compatible UBVRI filters - but they could make the filters better. The new generation of Baader Planetarium UBVRI filters, introduced at the end of 2021, is a modern filter set that is both fully compatible with the characteristics of the original Bessel filters and at the same time meets modern demands for contemporary filters:

The photometric filters now have the same thicknesses as all other Baader filters:
2 mm filter thickness for all filters up to size 2" mounted (1.25", 31 mm, 36 mm, 2")
3 mm filter thickness for all sizes above (50.4 mm, 50 x 50 mm, 65 x 65 mm, 100 x 100 mm)


This means that they fit into any commercially available filter wheel, for which the original filters were often simply too thick and could not be fixed securely.

They are parfocal with all other Baader filters of the same size and now also available in sizes up to 100x100 mm - large enough even for modern, professional sensors, or optimal for easy handling in the common filter mounts for amateur telescopes.

The coating of all photometric filters is manufactured in the same technology as the CMOS-optimized narrowband and LRGB filters. The lifetime Life-Coat™ guarantee also applies here.

Ready for the future

At a time when common filter types often disappear from the market without warning, with these filters Baader wants to offer all users a way to build on previous data obtained with UBVRI or Sloan filters. Long-term availability makes it possible for amateurs to enter with a limited budget and a small set of filters to expand in the long term. Therefore, Baader has resisted the temptation to improve the filter lines and has done the utmost to improve the filters in durability and applicability.

CMOS optimized filters from Baader-Planetarium
The completely redesigned, CMOS-optimized filters from Baader work excellently with all CMOS cameras. The new ultra-sensitive CMOS sensors require special filters to get the most out of the images. These sensors are much more sensitive to reflections and halos. Baader has taken this trend into account with the new CMOS-optimized filters. The filters are the new standard in astrophotography with CMOS sensors.

The features of the new CMOS-optimized filters from Baader:
Increased contrast due to narrower full width at half maximum (FWHM);
Reflex blocker coatings for maximum insensitivity to reflections with correctors, reducers and similar auxiliary optics;
All filters have identical thickness for parfocality - no need to refocus due to different filter thicknesses;
All filters have blackened edges with filter front side marking (black outer edge at the front side), thus additionally avoiding any reflection also at the filter edge;
Each filter is individually fine optically polished and coated, with sealed coating edge. This prevents the penetration of moisture.
Life-Coat stands for an even harder and age-resistant coating, thus the fiter can withstand the most adverse conditions and offers full filter performance even after years;
Each filter comes in a stackable filter box for optimal storage and transport;


Life-Coat™: „Limited-Lifetime-Warranty” for CMOS-optimized Baader filtersFilters equipped with Baader Planetarium´s Life-Coat™ technology are so durable that Baader Planetarium guarantees the coatings for the life of the filter. Baader Planetarium has developed Life-Coat™ using materials and processes that result in coatings that will not degrade or age for the life of the filter. Life-Coat™ coatings resist moisture, temperature extremes and are hardened to withstand normal cleaning.

Baader Planetarium guarantees that the Life-Coat™ coatings will not peel, flake or physically degrade and will withstand repeated cleaning with fine optical cleaning agents. This limited lifetime warranty applies to the original purchaser and does not cover failures due to misapplication, physical damage due to improper handling or improper cleaning.
Filter type:Bandpass
Single or in set:Single filter
Filter usage:CMOS, CCD, UBVRI
Transmission range:Transmission according to Bessel
CWL (central wavelength):Bessel UBVRI-B
Coating (antireflection coating):Reflex-Blocker™ hard-coated, plano-optical polished.
Special features:Life-Coat™ warranty
Filter shape:round
Filter size:31 mm
Filter thickness:2 mm
Filter mount:unmounted
Color:Black
Net weight (kg):0.06
Filter
Protective container



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