What is the Chroma U-Bessell filter primarily used for?
The Chroma U-Bessell filter is designed for scientific photometry. It isolates the ultraviolet (UV) band of the standard UBVRI system, allowing astronomers to accurately measure the brightness and color of celestial objects to determine physical properties like temperature and composition.
Is the Chroma U-Bessell filter parfocal with other filters?
Yes. It is manufactured on a 3.0 mm thick substrate, making it parfocal with all other Chroma astronomy filters (with the exception of the LoGlow filter). This means you can switch between filters in a filter wheel without needing to refocus your telescope.
What does a transmitted wavefront of "better than 0.25 waves/inch" mean for my images?
It describes how little the filter distorts light passing through it. A transmitted wavefront better than 0.25 waves per inch means the Chroma U-Bessell filter adds very little wavefront error, which helps preserve the sharpness of your telescope's optics.
How does the construction of the Chroma U-Bessell filter improve its durability?
Chroma uses durable sputtered hard coatings on a single, non-laminated glass substrate. This method creates an extremely resilient surface that resists humidity, temperature changes, and routine cleaning.
Can I use the Chroma U-Bessell filter with a fast telescope like an f/2 system?
Chroma does not publish a focal-ratio rating or f/# data for its photometric filters. All interference filters shift toward the blue in fast beams; a broadband filter is less affected than a narrowband one, but for strict photometry, check with Chroma before using a very fast system.
What is the difference between mounted and unmounted versions of the Chroma U-Bessell filter?
Mounted filters (1.25" and 2") come in a threaded ring (M28.5x0.6 and M48x0.75 respectively) ready to be screwed into a filter wheel or eyepiece. Unmounted filters (31mm, 36mm, 50mm round, and 50x50mm square) are bare glass intended for filter drawers or wheels that use retaining rings to hold the filter in place.
When would I use the U-Bessell filter instead of a B or V filter for observing a variable star like Algol (Beta Persei)?
For a hot, blue star like Algol, the greatest variation in brightness occurs in the ultraviolet and blue parts of the spectrum. The U-Bessell filter would capture the most dramatic changes in its light curve during an eclipse. The B (Blue) and V (Visual/Green) filters would show progressively less variation, providing color information that reveals temperature changes as the secondary star passes in front of the primary.
Does the Chroma U-Bessell filter come with a warranty?
Yes. All Chroma sputtered catalog filters, including the U-Bessell, are covered by the Chroma lifetime warranty against manufacturing defects under normal use. They are manufactured in Vermont, USA.
