The Baader Bessel U Photometric Filter one filter in a full collection of five. The U filter passes light centred on 364 nanometres.
Bessel photometric filters pass light in colour groups named: ultraviolet; blue; visible; red; and infrared. Using these filters you will be able to accurately assess the amount of light emitted by the target in these five corresponding frequency bands.
The UBV photometric system (from Ultraviolet, Blue, Visual), also called the Johnson system (or Johnson-Morgan system), is a photometric system usually employed for classifying stars according to their colours. It was the first standardized photometric system. The apparent magnitudes of stars in the system are often used to determine the colour indices B−V and U−B, the difference between the B and V magnitudes and the U and B magnitudes respectively.
The UBVRI system was extended to include the R and I filters for the red region of the spectrum.
- Baader Bessel-UBVRI Bandpass Filter Set, suitable for instruments from f/15 to f/1.8
- Classic photometric filters with transmission according to Bessel – parfocal with all Baader filters of the same size
- Manufactured with most advanced ion beam coating technology / Daylight-Proof
- Reflex-Blocker™ hard coated and planeoptically polished – with sealed coating edges (Life-Coat™)
- Blackened edges all around, with filter-lead-side-indicator in the form of a telescope-sided black outer rim
- Equally suitable for modern CMOS cameras as well as for older CCD camera technologies
The filter set 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)
- 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 100x100mm – 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.
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